U.S. patent application number 11/626148 was filed with the patent office on 2008-05-08 for heat treatment of inlaid pressure vessels.
Invention is credited to Philip A. Huff, Keith Pruden.
Application Number | 20080105341 11/626148 |
Document ID | / |
Family ID | 39358716 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080105341 |
Kind Code |
A1 |
Huff; Philip A. ; et
al. |
May 8, 2008 |
HEAT TREATMENT OF INLAID PRESSURE VESSELS
Abstract
A process to manufacture an oilfield component comprises
selectively reinforcing a base material with an age-hardenable clad
material and selectively heating at least a portion of the clad
material such that it age-hardens and the base material remains at
less than the tempering temperature of the base material. A body of
a ram blowout preventer comprises, a low-ally base material, a
vertical bore through the body and a horizontal bore through the
body intersecting the vertical bore, wherein the body is heat
treated by a process comprising selectively heating at least a
portion of the clad material such that the clad material
age-hardens and the base material remains at less than the
tempering temperature of the base material.
Inventors: |
Huff; Philip A.; (Spring,
TX) ; Pruden; Keith; (Katy, TX) |
Correspondence
Address: |
OSHA LIANG L.L.P.
1221 MCKINNEY STREET, SUITE 2800
HOUSTON
TX
77010
US
|
Family ID: |
39358716 |
Appl. No.: |
11/626148 |
Filed: |
January 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11555984 |
Nov 2, 2006 |
|
|
|
11626148 |
|
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|
|
Current U.S.
Class: |
148/622 ;
148/328; 148/559; 148/675 |
Current CPC
Class: |
B32B 15/015 20130101;
C22C 19/058 20130101; C22C 38/04 20130101; C21D 9/14 20130101; C21D
2251/04 20130101; C22C 19/056 20130101; C21D 6/001 20130101; C21D
9/08 20130101; C21D 2221/02 20130101; C21D 6/02 20130101; C21D
2251/02 20130101; C22C 19/055 20130101; C21D 6/004 20130101; C22C
38/02 20130101; C22C 38/22 20130101; B32B 15/011 20130101; C21D
9/50 20130101; C21D 2221/00 20130101; C22C 38/44 20130101; C21D
6/002 20130101; C21D 9/0068 20130101 |
Class at
Publication: |
148/622 ;
148/328; 148/559; 148/675 |
International
Class: |
C21D 9/00 20060101
C21D009/00; C22C 38/00 20060101 C22C038/00 |
Claims
1. A process to manufacture an oilfield component, the process
comprising: selectively reinforcing a base material with an
age-hardenable clad material; and selectively heating at least a
portion of the clad material such that it age-hardens and the base
material remains at less than the tempering temperature of the base
material.
2. The process of claim 1, wherein the base material comprises a
fully tempered forging.
3. The process of claim 1, wherein the base material comprises a
snap-tempered forging.
4. The process of claim 3, further comprising finish tempering the
oilfield component at a selected time and at a selected temperature
to temper the base material and age harden the clad material.
5. The process of claim 1, further comprising active cooling at
least a portion of the base material.
6. The process of claim 5, wherein the active cooling comprises
contacting a heat exchange medium with at least a portion of a
surface of the base material.
7. The process of claim 6, wherein the heat exchange medium
comprises at least one of air and water.
8. The process of claim 1, wherein the base material remains at
least 50.degree. F. below the tempering temperature of the base
material.
9. The process of claim 1, wherein the base material remains at
least 75.degree. F. below the tempering temperature of the base
material.
10. The process of claim 1, wherein the selectively heating
comprises heating the clad material using ceramic electric heating
blankets.
11. The process of claim 1, wherein at least a portion of a surface
of the base material is maintained at a temperature of 100.degree.
F. or less during the selectively heating.
12. The process of claim 1, wherein the clad material comprises a
thickness of at least 0.5 inches.
13. The process of claim 1, wherein the base material comprises at
least one of 4130 low-alloy steel, Grade F22 low-alloy steel, and
Grade 8630 Modified low-alloy steel.
14. The process of claim 1, wherein the clad material comprises at
least one of INCONEL 725, Alloy 718, Alloy 625, and 17-4PH
stainless steel.
15. The process of claim 1, wherein the base material remains at or
below 1180.degree. F.
16. The process of claim 1, wherein at least a portion of the clad
material is selectively heated to a temperature between about
1250.degree. F. and about 1400.degree. F.
17. The process of claim 1, wherein the selective heating results
in the clad material having a yield strength of at least 115 ksi
and the base material having a maximum Brinell hardness of 237.
18. The process of claim 1, wherein the oilfield component
comprises at least one of a blowout preventer body, a stress joint,
a valve body, a wellhead, a choke valve, and a sucker rod.
19. A ram blowout preventer manufactured using the process of claim
1.
20. A body of a ram blowout preventer, comprising: a low-alloy base
material; a vertical bore through the body; a horizontal bore
through the body intersecting the vertical bore; wherein at least a
portion of the body is selectively reinforced with a clad material;
and wherein the base material is heat treated by a process
comprising selectively heating at least a portion of the clad
material such that the clad material age-hardens and the base
material remains at less than the tempering temperature of the base
material.
21. The body of the ram blowout preventer of claim 20, wherein the
body comprises a flange neck selectively reinforced with the clad
material.
22. The body of the ram blowout preventer of claim 20, wherein the
body is selectively reinforced based upon a result of a finite
element analysis.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit, pursuant to 35
U.S.C. .sctn.120, as a Continuation-In-Part application of U.S.
patent application Ser. No. 11/555,984 filed on Nov. 2, 2006, and
entitled "Heat Treatment Method of Inlaid Pressure Vessels," which
is expressly incorporated by reference in its entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments disclosed herein relate generally to oilfield
components and equipment used during oil and gas production.
Specifically, embodiments disclosed herein relate to a method of
heat treating oilfield components.
[0004] 2. Background
[0005] A variety of designs exist for the drilling and production
of hydrocarbons, including onshore and offshore drilling and
production units. Offshore drilling and production unit designs may
vary based upon water depth and the type of platform used, such as
floating platforms, semi-submersible platforms, tension leg
platforms, spar-type platforms, and others as are known in the art.
Offshore units also vary in the type and location of control
devices, including wet-tree systems, where the control devices are
located atop a wellhead on the sea floor, and dry-tree systems,
where the control devices are located on the platform.
[0006] Components used during the drilling and production of oil
wells, regardless of the location and design, are subject to
corrosion, wear, and fatigue. For example, with respect to offshore
drilling and production, components and equipment used are subject
to a dynamic environment, where near-surface and sub-surface
currents may impart bending, tension, and/or rotational stress. In
a typical deepwater offshore production, for example, a riser
extends between a floating platform, at the surface of the ocean,
and the wellhead, at the sea floor. Because the wellhead is
statically located at the sea floor and the riser and the platform
or drilling rig are motive, the imparted stresses may fatigue
production components, including buoyancy devices, stress-relief
subs, pad-eye connections for ballast or tension lines, stress
joints, blowout preventers ("BOPs"), well control assemblies, mud
lift modules, ballast weights, and other components known in the
arts Each of these components, including the connections at the
platform, the riser joints, and the wellhead components, may
experience stress and strain associated with the dynamics of the
offshore environment.
[0007] As another example of components subject to wear, corrosion,
and fatigue, "rod" pumps are often used during the production of
oil and gas from a reservoir. This deep well pump is mechanically
activated by a walking beam pumping unit which is connected by one
end to a power source and by the other end to a string of steel
rods (e.g., sucker rods) that interconnect themselves to form a
string of rods extending to the inside of the well, with the string
connected by its other end to the deep well pump. During pumping,
the string of rods performs a reciprocating or rotating movement,
which may produce deflections of the string. The sucker rods are
thereby subjected to wear due to frictional contact with the inner
wall of the production tubing. Even though the fluid environment
serves as a lubricant, abrasion does occur over the surface of the
sucker rods. Additionally, tools used during assembly, such as
those used for centering the string, may cause tearing of the rod
surface. In the case of hydrocarbon wells, the fluid includes
dissolved salts and undissolved minerals which may have an
additional abrasive effect on the rod surface. At the same time
that abrasion occurs, the metal in the sucker rods is subjected to
a hard corrosive attack caused by downhole chemicals. These rods
also experience very high cyclic axial tension over their service
life and may be subject to axial fatigue.
[0008] In addition to the dynamic, abrasive, and corrosive stresses
briefly described above, oilfield components may also be subject to
fatigue due to the high pressures and temperatures encountered
during the drilling and production process. The process of drilling
wells involves penetrating a variety of subsurface geologic
structures, or layers called "formations." Occasionally, a wellbore
will penetrate a formation having a formation pressure
substantially higher than the pressure maintained in the wellbore.
When this occurs, the well is said to have "taken a kick." The
pressure increase associated with the kick is generally produced by
an influx of formation fluids (which may be a liquid, a gas, or a
combination thereof) into the wellbore. The relatively high
pressure kick tends to propagate from a point of entry in the
wellbore uphole (from a high pressure region to a low pressure
region). The normal operating pressures and the high pressure kicks
subject the oilfield components to additional fatigue.
[0009] In the past, oilfield components subject to fatigue loading
conditions were manufactured from a single metallic alloy. The
alloys normally utilized are generally low-alloy steels processed
by heat treatment to the mechanical properties suited to the
loading conditions. The use of a high strength nickel-based alloy
in the manufacture of these parts would normally be cost
prohibitive.
[0010] In many cases, these oilfield components may need to meet
the design criteria for metallic oil and gas field components, such
as those requirements established by NACE International (formerly
the National Association of Corrosion Engineers) and the European
Federation of Corrosion for the performance of metals when exposed
to various environmental compositions, pH, temperature, and
H.sub.2S partial pressures. For example, NACE MR0175 limits the
maximum hardness of the parts to Rockwell C 22 or Brinell 237 for
low-alloy steels in the quenched and tempered condition.
[0011] For most low-alloy steels, the maximum yield strength that
they are able to reach under the NACE maximum hardness limitation
is about 80,000-90,000 psi. Very few low-alloy steels are able to
develop this yield strength and hardness combination in a section
thickness having any useable significant size. For example, when
the section thickness is more than four to six inches, many
low-alloy steels cannot develop the desired mechanical properties
on quench and temper throughout their entire section thickness at
the time of heat treatment.
[0012] Since fatigue life may be affected by the amount of stress
imposed on a material relative to its yield strength, many
materials exhibit a shorter life in fatigue when the stress applied
exceeds as low as 50% of its yield strength. Consequently, if the
parts are used in fatigue loading conditions such as those defined
in NACE MR0175, the allowable applied stress may be limited to 50
to 65 ksi or less.
[0013] If fatigue failure occurs at these stress levels, there is
little that may be done other than to reduce the applied stress by
reducing the load on the part. Because the mechanical strength of
the alloy cannot be increased significantly without exceeding the
maximum hardness value mandated by NACE MR0175, reducing the
applied stress was the only solution formerly available.
Furthermore, fatigue strength is dependent on ductility as well.
Thus, because ductility and strength are inversely related material
properties, raising the strength of a material to accommodate
fatigue properties may be counterproductive.
[0014] Fatigue failure is a phenomenon that results from high
tensile stress at the surface or within close proximity to the
surface of a material. Therefore, surface modification procedures,
such as shot peening, case hardening by nitriding or carburizing,
and flame hardening or induction hardening, have been used to
increase the fatigue strength of a material by leaving a residual
compressive stress at the surface. Parts that contain a residual
compressive stress at their surface are less likely to fail in
fatigue since cracking is more difficult to initiate and/or
propagate when the part is residually loaded in compression.
[0015] While these surface modification procedures may aid in
reducing or eliminating fatigue failures, shot peening and
nitriding are superficial while carburizing and flame or induction
hardening generally are not capable of modifying the material
properties to depths below the surface of more than approximately
0.050 inches. Furthermore, these surface modification methods may
be at odds with or violate the requirements of NACE MR0175 for use
of the equipment in sour service or seawater environments. For
example, the hardness induced on the surface or near subsurface of
a part may be in excess of the threshold value for sulfide or
chloride stress corrosion cracking.
[0016] As mentioned above, the lifespan of an oilfield component
may also be affected by corrosion, such as by exposure to H.sub.2S.
For many years, parts in the oil tool industry have been clad
overlaid on the ring grooves, sealing areas, and wetted surfaces
solely for the prevention of damage to the base metal from the well
bore fluid. For example, U.S. Pat. No. 6,737,174 discloses a sucker
rod having a surface coated by a copper alloy. In other clad
overlay processes, a corrosion resistant alloy ("CRA") clad layer,
such as nickel based Alloy 625 (i.e., INCONEL 625) has been applied
in thicknesses nominally from 0.060 to 0.187 inches to protect a
base metal from corrosive attack. Other CRAs may be used in these
applications, but the industry has essentially standardized Alloy
625 for CRA cladding of oil tool equipment. There has been little
if any attention paid to the strength of the cladding material
except to assure that the strength of clad layer material is equal
to or greater than the strength of the base metal in the part.
[0017] Oilfield components and parts having an increased service
life are desired, including parts subject to high temperatures,
corrosive fluids, high stress levels, and/or fatigue loading
conditions, including cyclic loading conditions. Accordingly, there
exists a need for oilfield components that have improved
performance under various extreme operating conditions, including
fatigue loading conditions.
[0018] In the prior art, ram and annular BOP bodies, as well as
accessory equipment, have typically been manufactured for use in
operating pressures up to 15,000 psi and temperatures up to
250.degree. F. These BOP bodies are manufactured using one-piece,
rough machined, and heat treated low-alloy steel forgings or
multiple piece low-alloy steel forgings that have been rough
machined, heat treated and fabrication welded together. Castings
have been and still may be used for the manufacture of these ram
BOP bodies for these service conditions as well as forgings.
[0019] In the prior art, one-piece single, dual, or triple ram BOP
bodies, which may be produced from low-alloy steel Grade F22, are
quenched and final-tempered to meet the final material
specification requirements. Alternatively, fabricated BOP bodies
may be fabricated by welding together low-alloy steel Grade 8630
Modified quenched and final-tempered parts. The bodies are then
machined to near net shape and weld overlaid with a corrosion
resistant alloy, such as, AISI 316 austenitic stainless steel or
nickel base Alloy 625 in the API ring grooves, bonnet faces and
internal top seal area and other areas designated on the
engineering drawings.
[0020] After fabrication welding and/or overlay welding, the BOP
bodies are conventionally given a post-weld heat treatment
("PVVHT") at a temperature dependant on the steel grade from which
the parts have been produced. The purpose of the PWHT is primarily
to reduce the hardness of the heat affected zone ("TAZ") of welded
areas to the maximum hardness levels mandated by NACE MR0175 of HRC
22 or Brinell 237 for resistance to sulfide stress corrosion
cracking ("SCC").
[0021] This PWHT is mandated by the controlling welding
specification, ASME Section IX, to be performed at a temperature
below the tempering temperature of the base metal itself. The PWHT
operation tends to reduce the mechanical properties of the base
metal and limits the number of times that a particular BOP body can
be welded and post-weld heat treated before the mechanical
properties of the base metal have been degraded to a level below
the minimum requirements for the base metal required for the part.
After the PWHT operation has been performed, the bodies are then
finish machined to their final dimensional configuration.
[0022] As detailed in the current disclosure, the prior art
manufacturing procedure may be changed to use a high strength, age
hardenable, corrosion resistant alloy, CRA, to selectively
reinforce areas of the one piece body for encapsulation of the high
surface or near subsurface stresses in the BOP body. This change
may allow manufacture of BOP bodies for use at operating pressures
above 15,000 psi and at operating temperatures up to 350.degree. F.
and above.
[0023] However, if the prior art method of manufacture were used,
as described above, the PWHT temperature would be sufficient to
obtain the required maximum HAZ hardness value but the PWHT
temperature would be too low to obtain the required mechanical
properties in the age hardenable CRA overlay material. If the PWHT
temperature were increased to obtain the mechanical properties in
the CPA overlay material, the PWHT temperature would equal or
surpass the tempering temperature of the Grade F22 base material of
the BOP body, which is prohibited by ASME Section IX.
[0024] For example, where the CRA filler metal for the clad overlay
weld deposition is INCONEL 725 and the base material is Grade F22
low-alloy steel, the Grade F22 steel must be post-weld heat treated
at a minimum temperature of 1150.degree. F. (621.degree. C.) for a
period of time ranging from four to eight hours or more. The Grade
F22 low-alloy steel with section thickness of eight inches and
greater will be quenched and tempered to develop a minimum yield
strength of 85,000 psi. To develop this minimum yield strength
requires a tempering temperature of 1150.degree. F. to 1250.degree.
F. (621.degree. C. to 677.degree. C.) for a period of time of eight
to ten hours or more. However, since the INCONEL 725 is an age
hardenable alloy, in order to develop its mechanical properties on
the order of 120,000 psi minimum yield strength, it must be aged at
a temperature of 1200.degree. F. (649.degree. C.) for a minimum
period of time of eight to twenty four hours. All of these various
tempering temperatures and times, PWHT temperatures and times, and
the age hardening temperatures and times may be in conflict with
one another.
[0025] If the base metal is conventionally quenched and
final-tempered as described above, the age hardening temperature
and time for the INCONEL 725 would further temper the Grade F22
base metal, likely lowering its mechanical properties below the
minimum specification requirement. If the INCONEL 725 weldment
joint on the Grade F22 were PWHT as described above, the maximum
HAZ hardness would be met and the mechanical properties of the
Grade F22 would be preserved, but the INCONEL 725 weld metal would
likely not develop the mechanical properties in the overlay that
are desired.
[0026] Accordingly, there exists a need for methods of manufacture
to obtain parts meeting the requirements for HAZ hardness and
mechanical properties for both the base metal and the clad overlay
for use in oilfield service.
SUMMARY OF INVENTION
[0027] In one aspect, embodiments disclosed herein relate to a
process to manufacture an oilfield component comprising selectively
reinforcing a base material with an age-hardenable clad material
and selectively heating at least a portion of the clad material
such that it age-hardens and the base material remains at less than
the tempering temperature of the base material.
[0028] In another aspect, embodiments disclosed herein relate to a
body of a ram blowout preventer comprising a low-alloy base
material, a vertical bore through the body, a horizontal bore
through the body intersecting the vertical bore, wherein at least a
portion of the body is selectively reinforced with a clad material,
and wherein the base material is heat treated by a process
comprising selectively heating at least a portion of the clad
material such that the clad material age-hardens and the base
material remains at less than the tempering temperature of the base
material.
[0029] Other aspects and advantages will be apparent from the
following description and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
[0030] FIG. 1 is section view drawing of a flange neck reinforced
in accordance with embodiments disclosed herein.
[0031] FIG. 2 is a block diagram of a process to manufacture an
oilfield component in accordance with embodiments disclosed
herein.
[0032] FIGS. 3A and 3B are schematic drawings of a base material
having various configurations of a clad inlay.
[0033] FIGS. 4A and 4B compare simulation results for selective
heat treatment of a clad inlay with forced cooling and selective
heat treatment of a clad inlay with natural convective cooling of
the base material.
DETAILED DESCRIPTION
[0034] In one aspect, embodiments disclosed herein relate to a
method of manufacturing or reinforcing oilfield components. In
other aspects, embodiments disclosed herein relate to the heat
treatment of oilfield components that have been selectively
reinforced to reduce or eliminate stress and/or fatigue failures.
In yet other aspects, embodiments disclosed herein relate to the
selective heat treatment of the selectively reinforced areas of the
oilfield components.
[0035] As used herein, "oilfield components" refer to flanges,
bonnets, spools, stress joints, blowout preventers, sucker rods,
subsea well assemblies, valves (e.g., choke valves), valve bodies,
wellheads, and other equipment and parts commonly used for the
drilling and production of oil and gas. Those skilled in the art
will recognize that, although not specifically disclosed or
described in detail, embodiments disclosed herein may apply to
other oilfield components.
[0036] Component Design and Analysis
[0037] During transport, installation, and operation, oilfield
components experience stress and strain based on fatigue loading
conditions, many of which may occur on a continuous,
semi-continuous, or cyclic basis. Loading conditions may include
thermal loading, pressure loading, or mechanical loading. For
example, thermal loading may occur when a wellbore is hot (e.g.,
300.degree. F.) and is located in 10,000 feet of water at
32.degree. F. Pressure loading may result from internal (wellbore)
pressure acting outward on the oilfield component or from
hydrostatic (e.g., subsea) external pressure acting inward,
Further, mechanical loading may include bonnet and flange bolt
tightening preloads, axial tensile and compressive loads, and
bending moments. As such, the loading conditions may include at
least one of internal pressure, external pressure, axial tension,
axial compression, longitudinal tension, longitudinal compression,
axial bending moment, longitudinal bending moment, riser tension
and bending, and temperature extremes, among other load states. The
intensities of the local stress states placed on the equipment
during these loading conditions may have a significant impact on
the cyclic life of the equipment. Analyzing the performance of an
oilfield component subject to various fatigue loading conditions
may provide for enhancing the design and/or improving the
performance of the oilfield components to extend the useful life of
the oilfield component.
[0038] Finite element analysis ("FEA") is a useful and powerful
technique for analyzing stresses and strains in structures or
components too complex to analyze by strictly analytical methods.
With FEA, the structure or component is broken down into many small
pieces (a finite number of elements) of various types, sizes and
shapes. The elements are assumed to have a simplified pattern of
deformation (linear, quadratic, etc.) and are connected at "nodes"
normally located at corners or edges of the elements. The elements
are then assembled mathematically using basic rules of structural
mechanics, i.e., equilibrium of forces and continuity of loads,
resulting in a large system of simultaneous equations (a mesh).
[0039] By solving this large simultaneous equation system with the
help of a computer, the deformed shape of the structure or
component under load may be obtained, from which stresses and
strains may be calculated. Suitable software to perform such FEA
includes ABAQUS (available from ABAQUS, Inc.), MARC and PATRAN
(available from MSC Software Corporation), and ANSYS (available
from ANSYS, Inc.), among others. Finite elements of any shape known
in the art may be used. Hexagonal elements, though, are typically
highly stable and may be beneficial when simulating high stresses
and strains across a model.
[0040] A simplified design and/or model of an oilfield component to
assist in the analysis of the oilfield component may be used. For
example, the analysis of stress and strain concentrations of
complex component designs may be simplified by "smoothing" that
design. As used herein, the term "smoothing" refers to various
techniques to simplify a complex geometry of a design for use with
FEA. For example, internal corners may be modified to reduce or
eliminate their radii in an attempt to simplify a subsequently
constructed model. These techniques may allow the analysis of a
smoothed model (i.e., an FEA model constructed from a smoothed
design) to correlate and converge to a definitive result when
analysis of a non-smoothed model may not. As such, a model
constructed from a smoothed design may be analyzed with FEA to
determine an overall, or bulk, stress condition. By analyzing the
bulk stress, the performance, and possible failure, of an oilfield
component under various fatigue loading conditions may be
predicted.
[0041] One objective of FEA may be to isolate high stress or strain
areas and identify the areas that are prone to low cyclic life. The
results of a finite element analysis, analyzing the performance of
the component under various fatigue loading conditions, may be used
to identify regions subject to fatigue failure in the oilfield
component. Once the regions subject to fatigue failure are
identified, these areas may be re-designed or may be marked for
metallurgical processing, such as selective reinforcement, as will
be described later.
[0042] Possible load states or fatigue loading conditions for the
component should be determined for input into the FEA. As mentioned
above, these may include normal operating pressure, high-pressure
kick, riser tension and bending, and temperature extremes, among
other load states. The fatigue loading condition data should
include typical or expected values as well as maximum and/or
minimum values and the frequency at which these loads fluctuate to
enable a complete analysis.
[0043] Properties of the base material used to form the oilfield
component should also be determined, establishing the maximum
allowable peak stress value (SBpeak). The material properties may
either be determined through empirical testing or, in the
alternative, may be provided from commercially available material
properties data. For example, this value may be established based
on field tests where, under NACE environments (i.e., environments
established by NACE International for testing of oil and gas field
equipment), the stress would just meet the life cycle requirement
and would be less than the stress at which sulfide stress corrosion
cracking would occur.
[0044] More particularly, the tensile properties of the base
materials may be determined. The tensile strength of a material is
the maximum amount of stress (in tension) a material may be
subjected to before failure. As stress is exerted upon a material,
the material strains to accommodate the stress. Once the stress is
too much for the material, it will no longer be able to strain, and
the material fails. The failure point of the material is known as
the ultimate tensile strength.
[0045] The loading conditions and material properties may then be
used to analyze the oilfield component using FEA based methods. All
permutations for design and operating loads should be considered to
generate a complete analysis of the component. Proper bolt preloads
and material characteristic data, de-rated based on temperature,
should also be used.
[0046] A model (i.e., a mesh of simultaneous equations) for the
oilfield component is generated for use in the finite element
analyses. A three-dimensional model of the component may be
generated with specific design features. These design features may
be selected to give specific performance characteristics. Thus,
generating a model may also include the steps of importing a
component design to generate the model and smoothing the imported
design. The design may have various smoothing techniques applied
thereto to simplify FEA analysis. The models may be generated from
a design in a computer aided design ("CAD") software package (e.g.,
AutoCAD available from Autodesk, Inc., and Pro/Engineer available
from Parametric Technology Corporation) and imported into the FEA
software package. Alternatively, the model may be generated within
the FEA packages (e.g., ABAQUS and PATRAN) themselves.
[0047] Next, the loading conditions may be simulated upon the
component in FEA using the model. Preferably, these simulated
fatigue loading conditions reflect the load states or stress that
the oilfield component may expect to experience under normal use.
Further, after simulating fatigue loading conditions upon the
model, a stress plot from the loading conditions showing the stress
and deformation occurring in the oilfield component model may be
analyzed. The stress plot may determine and show the location and
amount of stress occurring in the oilfield component model from the
simulated loading conditions across the component.
[0048] The stress plot may be analyzed and reviewed to determine
the performance and characteristics of the model. If the model may
be further improved, another model may be generated or the current
model may be re-generated (modified). This will allow the model to
be further simulated in FEA to determine its performance after
further modifications or models. Otherwise, if the model is
considered acceptable and meets any and/or all specified criteria,
the model may be used in the manufacture oilfield components, as
will be described below.
[0049] Selective Reinforcement
[0050] Objectives of the numerical methods (e.g., FEA analysis)
include identifying, isolating, and highlighting zones subject to
fatigue failure within the oilfield components. For example, the
stress states which may cause early failure under NACE environment
may be identified. The results of the FEA may be used to generate
stress and strain plots for identifying regions subject to fatigue
failure in the component.
[0051] The identified zones subject to fatigue failure may be
modified in the manufacture of the oilfield component. For example,
the zones may be marked out, in a spatial representation or
drawing, noting the depth and lateral extents (length and width) of
high stress areas subject to fatigue failure. A contour plot may be
drawn, showing the length, width, and depth of the local stress
areas. The surface location of the fatigue zones, for example, may
be transferred to appropriate manufacturer's drawings. The
identified fatigue zones may then be selectively reinforced with a
higher strength material bonding metallurgically with the base
material.
[0052] It may be possible, in some embodiments, to reduce or help
prevent fatigue failure by surface substitution methods. For
example, if some depth of the part base metal of low-alloy steel is
removed and replaced with a higher strength material and a
metallurgical bond with the base metal is developed, fatigue
failures may be reduced or eliminated. The higher strength alloy
may be any convenient alloy of the user's choosing that exhibits
the strength, ductility, and corrosion resistance required by the
design of the oilfield components or parts.
[0053] The higher strength material may include other low-alloy or
medium-alloy steels with higher strength and/or higher corrosion
resistance than the low-alloy steel base metal and would be capable
of withstanding the applied stresses with a lower ratio of applied
stress to yield strength. Lowering the ratio of applied stress to
yield strength of the higher strength material would reduce its
tendency to initiate fatigue cracking, fatigue crack propagation
and ultimate fatigue failure. For example, a high strength alloy
such as Alloy 625 may be used to replace and bond with the
low-alloy base metal. The choice of the cladding alloy that could
be substituted for the partial thickness of the base metal
substrate up to 0.500 inches or more would be made on the basis of
the ratio of the applied stress to the yield strength of the alloy
used for the clad layer.
[0054] In some embodiments, the base material may be selectively
reinforced with an inlay clad. In other embodiments, the base
material may be selectively reinforced with an overlay clad. The
clad inlay or overlay may be bonded to the base material using
pressure, heat, welding, brazing, roll bonding, explosive bonding,
weld overlaying, wallpapering, or a combination thereof. In some
embodiments, the cladding may be bonded to the base material using
an electric arc welding process, such as a submerged arc welding
("SAW") process or a tungsten inert gas ("TIG") welding process. In
other embodiments, the cladding may be bonded to the base material
using an electric arc weld cladding process, a hot isostatic
pressing cladding process ("HIP" cladding), auto-frettage cladding,
laser cladding, or a combination of any of these methods. In some
embodiments, one or more clad layers may be used, such as a single
clad having two layers (base plus clad), a double clad (having 3
layers), or a cladding of up to 7 or more layers.
[0055] In some embodiments, the base material may be selectively
reinforced with a clad inlay. The clad inlay, in various
embodiments, may be shrunk-fit or press fit into recesses cut in
the body of the oilfield component, and seam/seal welded in place.
In other embodiments, the clad inlay may be shaped according to the
FEA stress plots.
[0056] The clad inlay or overlay, in some embodiments, may have a
thickness or an average thickness of up to 0.625 inches or higher.
In other embodiments, the clad inlay may have an average thickness
in the range from about 0.010 inches to about 0.625 inches; from
about 0.050 to about 0.500 inches in other embodiments; and from
about 0.125 to about 0.375 inches in yet other embodiments.
[0057] In other embodiments, press-fit or shrink-fit component
parts manufactured of the high-strength alloy may be used in
conjunction with the oilfield components. For example, solid parts
(e.g., flanges, bonnets, valve bodies, etc.) made of a
high-strength alloy (e.g., INCONEL 725) may be seal welded to a
low-strength substrate after being pressed or shrunk-fit into a
body.
[0058] In other embodiments, the base metals in the identified
fatigue zones may be replaced with a higher strength material
bonding metallurgically to the base material. For example, the base
metals in the high stress areas may be ground or machined away and
replaced with a higher strength material bonding metallurgically to
the base material.
[0059] In some embodiments, the selective reinforcement is a clad
overlay of higher strength material over a base material. In other
embodiments, the selective reinforcement may be a clad overlay of
higher strength material in ground or machined recesses in a base
material.
[0060] The choice of the cladding alloy may be based on its ability
to resist corrosion, including stress corrosion cracking, and its
ability to add mechanical strength (e.g., by a metallurgical bond
to the low-alloy substrate) to the portion of the oilfield
component to which it is applied and intended to protect. In a
typical overlay, for example, the strength of the cladding material
is expected to at least equal the strength of the base metal to
which it is applied. That is, the weld deposited alloy (such as
Alloy 625) is expected to match the yield strength of the low-alloy
steel base metal (such as low-alloy steel having a yield strength
of 75,000 psi). It may be possible to apply a cladding of a higher
strength material in a thickness that will encapsulate the
localized stresses in the higher strength clad layer, resulting in
an oilfield component that will meet NACE or other standards for
oil and gas field components and equipment while meeting the
strength and fatigue requirements of the design.
[0061] In some embodiments, the base material may be F22 low-alloy
steel, a steel having approximately 2 weight percent chromium and 1
weight percent molybdenum. Alternatively, the base material may be
4130 or 8630 modified low-alloy steel. Those skilled in the art
will recognize that other materials, having appropriate corrosion
resistance, hardness, and tensile properties suitable for use in an
oil and gas environment, may also be used as a base material.
[0062] In some embodiments, the clad overlay or clad inlay may be
formed from high yield strength, precipitation-hardenable corrosion
resistant alloys, such as INCONEL 725, or INCONEL 725 NDUR, for
example. In other embodiments, the clad overlay or clad inlay may
be formed from high yield strength, precipitation-hardenable
corrosion-resistant alloys such as Alloy 718 or INCONEL 718 SPF. In
still other embodiments, the clad overlay or clad inlay may be
formed from other precipitation-hardenable corrosion-resistant
alloys such as 17-4PH, INCONEL 625 or INCOLOY 925. Those skilled in
the art will recognize that other high strength corrosion resistant
materials may also be used as a cladding. Preferably, the cladding
material is compatible with the base material and is a
precipitation-hardenable alloy.
[0063] The alloys for use as a cladding may be available in the
form of weld wire, powder, or strip filler metal for weld cladding
and may also be available in the form of a powder intended to be
used in a HIP cladding operation. These alloys may also be
available in other forms that may be used in an auto-frettage
cladding operation.
[0064] Once the cladding method or combination of cladding methods
has been chosen, the minimum thickness and locations of the clad
layer may be determined based on the results of the FEA stress
analysis. The required thickness or depth of the cladding may vary
depending upon the alloy used in forming the cladding, the bond
formed between the clad and the base materials, as well as the
dilution of the clad material resulting from the process used to
bond the clad material to the base material. Once the values and
location of the areas subject to fatigue failure have been
determined, the cladding alloy may be chosen. It may not be
necessary to clad the entire oilfield component. Particularly, only
portions of the component may need to be clad. Furthermore, it may
be possible to selectively place a much lower clad thickness in
lower stressed areas, thus preventing corrosion of those areas
subject to contact with the wellbore fluid.
[0065] As one example, referring now to FIG. 1, a schematic drawing
of a flange neck reinforced for fatigue control is illustrated. A
vessel body 10 is attached to an integral flange 12 by flange neck
14. Flange neck 14 may experience fatigue loading conditions due to
the movement of components attached to flange 12, due to the
tensioning of the bolts in bolt holes 16, internal pressure pushing
outward on the vessel body 10 due to a fluid in bore 18, and other
loading conditions. The outer diameter surface 20 of flange neck 14
and the inner diameter surface 22 of vessel 10 across the wall
thickness from the flange neck 14 are commonly subjected to high
fatigue loading conditions, and may be selectively reinforced using
clad inlays or clad overlays 24, 26, by the methods described
above. For example, a flange neck subjected to fatigue loading
conditions is the bottom flange on ram and annular blowout
preventer bodies used in a subsea wellhead assembly stack. These
ram and annular blowout preventer bodies in the stack are subject
to considerable cyclic bending loads which result in a severe
bending fatigue situation on the flange necks. Selective
reinforcement may additionally provide greater resistance to stress
corrosion cracking to these areas that are subject to fatigue
loading conditions.
[0066] As another example, drilling or production riser stress
joints may be selectively reinforced to reduce or eliminate fatigue
failures. This stress joint has in the past been manufactured from
a high strength titanium alloy which is capable of withstanding
much more bending deflection than a low-alloy steel because of the
much lower modulus of the titanium alloy compared to the low-alloy
steel. However, titanium components are very expensive and are not
characterized by "fatigue strength." While steel components exhibit
a fatigue strength, under which a component will not fail,
regardless of the number of cycles, titanium components will
eventually fail regardless of the magnitude of the cyclic loading.
Therefore, by selectively reinforcing a low-alloy steel, it may be
possible to manufacture a stress joint capable of withstanding the
bending and deflection associated with the stress joint for longer
times (i.e., more cycles) using a lower cost material.
[0067] As another example, sucker rods and other components of rod
pumps subject to high cyclic axial fatigue may be selectively
reinforced to reduce or eliminate fatigue failures. The use of a
high strength surface layer on the OD surface of sucker rods, for
example, may prolong the service life of these parts as well.
Moreover, a high strength corrosion resistant material would likely
reduce the effects of any corrosion fatigue induced from the
environment in which they are used.
[0068] As another example, valve bodies may be selectively
reinforced to reduce or eliminate fatigue failures, to reduce or
eliminate corrosion, and/or to be manufactured more economically.
In the case of certain valves (e.g., choke valves), the selective
reinforcing may also reduce or eliminate erosion caused by the high
velocity flows on the downstream (i.e., the low-pressure) side of
the choke valve.
[0069] As another example, blowout preventer bodies, in addition to
the flange necks, may also be subject to fatigue and may be
selectively reinforced to reduce or eliminate fatigue failures. As
described above, blowout preventers are installed to limit the
equipment that may be affected by a high pressure kick. There are
several types of blowout preventers, the most common of which are
ram blowout preventers and annular blowout preventers (including
spherical blowout preventers). Ram blowout preventers, for
instance, are currently manufactured in various bore size ranges,
and may have a working pressure range from 2,000 to 15,000 psi.
However, it may be desired to use ram blowout preventers at higher
pressure and higher temperature conditions (above 15,000 psi and
greater than 250.degree. F.). Particularly, ram blowout preventers
rated at working pressures of 20,000 psi, 25,000 psi, and higher
and working temperatures of up to 350.degree. F. or higher, may be
desired. For example, see U.S. patent application Ser. No.
11/528,873 titled "Reinforcement of Irregular Pressure Vessels" by
Huff and Khandoker, filed on Sep. 28, 2006, hereby incorporated by
reference in its entirety. Results of the above described FEA for
blowout preventers used under high temperature and/or high pressure
conditions indicate that selective reinforcement of various
sections of the blowout preventer, such as the choke and kill
pockets, may enable the blowout preventer to be used at the higher
temperatures and pressures.
[0070] The objectives of the above described numerical methods (FEA
analysis) include identifying, isolating, and highlighting zones of
high or peak stress (SBpeak) states within the BOP equipment. For
example, the stress states which may cause early failure under NACE
environment may be identified. The results of the BOP FEA may be
used to generate stress and strain plots for identifying regions of
high stress concentrations in the vessel.
[0071] In addition, stress and strain plots may be used to define a
critical section thickness ("CST") in a casting or forging used in
an oilfield component in order to accurately determine the
appropriate heat treatment time at a selected temperature. Critical
Section Thickness is defined as the largest thickness of a
component which must have certain minimum mechanical properties
through the entire thickness. For example, a lightly stressed,
thick walled portion of a pressure vessel or BOP may not require
80,000 psi yield strength through its entire thickness, but a
thinner portion may require 80,000 psi yield strength through the
entire thickness in that portion; in this example, the thinner
portion may have the CST. A total heat treatment time may comprise
a first time (expressed in minutes per inch of CST) and a second
time (expressed in hours) which are summed together. For the
purpose of this disclosure, the first time is called the "dwell"
time and the second time is called the "soak" time. For example, a
typical conventional heat treatment time may include 30 minutes per
inch of CST dwell time and one hour soak time. In this example, a
forging used in an oilfield component with a CST of 10 inches would
require 6 hours heat treatment time at a selected temperature
(i.e., 10 inches.times.30 minutes per inch dwell time plus 1 hour
soak time).
[0072] Furthermore, stress and strain plots may be used to isolate
areas where stresses exceed a selected percentage of base material
yield strength. For example, in particular alloys used as a base
material, areas in excess of 80% yield may not pass NACE
requirements (as discussed below), or may not provide an adequate
engineering safety factor in a particular application, for example,
operation at a particular combination of internal pressure and
temperature. For example, areas in a BOP where stresses may exceed
a selected percentage of base material yield strength include seat
pockets, the BOP pocket near the bonnet, and BOP inner bores
(vertical bores, horizontal bores, and the intersections of the
vertical and horizontal bores). These stress and strain plots may
also be used to calculate the depth of the high stress zones in
excess of a selected percentage of base material yield
strength.
[0073] The identified high stress zones may be modified in the
manufacture of a BOP. For example, the zones may be marked out, in
a spatial representation or drawing, noting the depth and lateral
extents (length and width) of high stress areas exceeding the
allowable SBpeak stress. A contour plot may be drawn, showing the
length, width and depth of the local stress areas in excess of a
selected percentage of the base material yield strength. The
surface location of the peak stress zones, for example, may be
transferred to appropriate manufacturer's drawings. The identified
high stress zones may then be selectively reinforced with a higher
strength material. In some embodiments, this higher strength
reinforcing material may be metallurgically bonded with the base
material.
[0074] Hardening
[0075] Selectively reinforced oilfield components, including flange
necks, blowout preventers, sucker rods, and other components,
particularly those exposed to corrosive fluids, may need to meet
the design criteria for metallic oil and gas field components, such
as those requirements established by NACE International (formerly
the National Association of Corrosion Engineers) and the European
Federation of Corrosion for the performance of metals when exposed
to various environmental compositions, pH, temperatures, and
H.sub.2S partial pressures (including NACE MR0175, NACE TM0177, and
NACE TM0284). For example, NACE MR0175 limits the maximum hardness
of the parts to Rockwell C 22 or Brinell 237 for low-alloy steels
in the quenched and tempered condition. These hardness limitations
must be met in addition to developing the desired yield strength
for the selectively reinforced areas.
[0076] However, meeting the hardness limitation while developing
the desired yield strength may require changes to the current
manufacturing techniques. Post-weld heat treatment temperatures and
times may be in conflict with the age hardening temperatures and
times. For example, where a low-alloy steel base material is
selectively reinforced with a nickel-based corrosion resistant
alloy (CRA), the post-weld heat treatment temperature may be
sufficient to obtain the required maximum hardness value for the
heat affected zone during welding of the clad overlay, but the PWHT
temperature may be too low to obtain the required mechanical
properties in the age-hardenable CRA overlay material.
[0077] To overcome these competing temperature and time
requirements, a method of manufacturing the selectively reinforced
oilfield components has been developed to procure the desired
properties in the base material and the material used to
selectively reinforce the base material. In one such method, a
casting, forging, or hot isotactic pressing used in an oilfield
component may be made from a base material including, but not
limited to, low-alloy steel. Appropriate low-alloy steels may
include, but are not limited to, 4130, 8630 Modified, and F22.
[0078] The base material may then be normalized. For example, an
F22 low-alloy steel forging may be normalized at 1750.degree. F.
for 30 minutes per inch of thickness plus one hour. If desired, the
castings, forgings, or hot isotactic pressings may then also be
rough machined into a desired configuration.
[0079] Following normalization, the castings, forgings, or hot
isotactic pressings may then be quenched and snap-tempered
("Q&ST") to prevent cracking. As used herein, "snap tempering"
describes an intermediate low temperature heat treatment that
softens the alloy slightly and decreases the likelihood of
cracking, especially so-called "autogenous" or "self" cracking. For
example, a component made from F22 may be Q&ST to
900-1000.degree. F. for a dwell time of about 30 minutes per hour
per inch of CST, plus a soak time of one hour. Optionally, the
rough machining described above may be performed after the snap
tempering. As-forged, as-cast, and as-pressed components may be
especially delicate and snap tempering after quench may allow them
to be handled, shipped, and/or further machined without
cracking.
[0080] Ordinarily, in conventional practice, castings, forgings,
and pressings used in oilfield components would be fully
heat-treated by processes including normalizing, austenitizing,
solution annealing, tempering, age-hardening, heat treating, and
other methods as known in the art to achieve the desired final
material properties before they are inlaid or overlaid with CRA
material. For example, according to conventional practice, a BOP
body made from a low-alloy steel such as, for example, 4130, 8630,
or F22, would be fully heat treated and at least partially machined
before it was weld-inlaid with a CRA material such as INCONEL 625
in, for example, the ring gasket grooves on its flanged
connections. In conventional practice, such an inlaid BOP body
would then be stress-relieved (that is, annealed) to some
temperature below the tempering temperature of the base material to
ensure that the yield strength of the base material is
preserved.
[0081] According to the current disclosure, the castings, forgings,
and pressings used in oilfield equipment, having undergone
Q&ST, may be finish-machined and selectively reinforced (as
described above) with a clad material without fully tempering the
castings, forgings, or pressings. Once selectively reinforced, the
clad material may be finish-machined (if necessary) to obtain their
final geometry. Furthermore, following selective reinforcement, the
oilfield component may then undergo a single heat treating step,
referred to herein as a "finish temper," for a selected period of
time at a selected temperature. In one embodiment, the selected
period of time is intermediate a time required to completely temper
the base material and a time required to age-harden the clad
material. Furthermore, the selected finish temper may provide for
one or more of (a) developing the required mechanical properties of
the base material, (b) post-weld heat treatment of a heat affected
zone of a welded joint between the base material and the clad
material, and (c) age hardening (also known as "precipitation
hardening") the clad material.
[0082] In another embodiment, the clad material may be further
strengthened by a "supplemental heat treatment" after the finish
tempering by the selective application of heat. For example,
ceramic electric heating blankets well known in the art may be used
to "supplementally age" the clad material. In an exemplary
embodiment of supplemental aging of the clad material, heat is
applied to the surface of the clad material with ceramic electric
heating blankets so that a temperature gradient is developed across
the cladding material and the base material, such that the
temperature of the base material is always less than the finish
tempering temperature (or, in particular, less than the finish
tempering temperature minus about 50-100.degree. F.).
[0083] In another embodiment, age-hardenable clad material may be
applied as selective reinforcement to a conventionally quenched and
final-tempered oilfield component (as discussed below), then the
cladding may be "supplementally aged" as above without affecting
the "final" temper.
[0084] In some embodiments, the finish-temper process is
facilitated by a nexus between the tempering temperature of the
base material and the age-hardening temperature of the clad
material. In some embodiments, the base material may have a
tempering temperature within 100.degree. F. of an aging temperature
of the clad material. In other embodiments, there may be as few as
75.degree. F. or 50.degree. F. separating the two temperatures.
[0085] Thus, in some embodiments, the time required by both the
desired tempering cycle and the desired age-hardening cycle are
such that they may coincide at a total finish temper time (dwell
time plus soak time), achieving the properties required of both the
base material and the clad material. In other embodiments, the time
required by both the tempering cycle and the age hardening cycle
are such that a total finish temper time intermediate a desired
tempering time and a desired age-hardening time may achieve the
properties required of both the base material and the clad
material.
[0086] The finish temper, as mentioned above, may result in the
desired properties for both the base material and the clad
material. In some embodiments, the finish temper may result in the
base material developing a yield strength of between 80 ksi and 95
ksi. In other embodiments, the finish temper may result in the clad
material developing a yield strength of at least 115 ksi. In yet
other embodiments, the finish temper may result in an oilfield
component with a base material having a maximum hardness of HRC 22
or Brinell 237. In selected embodiments, these properties are met
for each component.
[0087] In some embodiments, the finish temper temperature may be
between about 1200.degree. F. to about 1300.degree. F.; between
about 1225.degree. F. and 1300.degree. F. in other embodiments; and
between 1215.degree. F. and 1225.degree. F. in yet other
embodiments. In some embodiments, the finish temper temperature may
be greater than a post-weld heat treatment temperature of the base
material.
[0088] In some embodiments, the finish temper time of the
selectively reinforced oilfield component may be 30 to 60 minutes
per inch of CST "dwell" time plus one to two hours "soak" time. In
other embodiments, the finish temper time for the selectively
reinforced component may be 30 to 45 minutes per inch of CST
"dwell" time plus one to two hours "soak" time. In still other
embodiments, the finish temper time may be 38 to 42 minutes per
inch of CST "dwell" time plus about one hour "soak" time.
[0089] As described above, embodiments disclosed herein may provide
a method for manufacturing a selectively reinforced oilfield
component. The oilfield component may include a base material
selectively reinforced with a clad material, and the method may
include finish tempering the oilfield component at a selected time
and temperature to temper the base material and age harden the clad
material.
[0090] Referring now to FIG. 2, a block diagram of a process for
manufacturing a selectively reinforced oilfield component in
accordance with embodiments disclosed herein is illustrated.
Manufacturing process 50 may include step 52, providing a base
material for an oilfield component. As one of ordinary skill in the
art should understand, providing 52 may include, but is not limited
to, forging or casting, hot isotactic pressing, rough machining of
the base material, and normalizing the base material. Next,
manufacturing process 50 may include quenching and snap tempering
(Q&ST) 56 of the treated base material. Following snap
tempering 56, the base material may be selectively reinforced 58
with a clad material. Selective reinforcing 58 may include, for
example, inlaying the base material with a corrosion resistant
alloy, where the corrosion resistant alloy may have a higher
strength than the base material. After selectively reinforcing 58,
the oilfleld component (i.e., the base material and the clad
material) may undergo finish temper 60. Finish temper 60 may
include finish tempering the oilfield component at a selected time
and temperature to temper the base material and age harden the clad
material.
[0091] Supplemental Age-Hardening
[0092] As described above, the clad material may be supplementally
age-hardened to increase the yield strength of the clad material.
Supplemental age-hardening may achieve the properties required of
both the base material and the clad material. Heat may be
selectively applied to at least a portion of the clad material, and
in some embodiments the clad material may develop a yield strength
of at least 115 ksi while the base material hardness remains
Brinell 237 or less.
[0093] Supplemental age-hardening may be performed on a selectively
reinforced Q&ST oilfield component in some embodiments. For
example, as described above, the castings, forgings, and pressings
used in oilfield equipment, having undergone Q&ST, may be
finish-machined, selectively reinforced without fully tempering the
castings, forgings, or pressings, and then finish tempered for a
selected period of time at a selected temperature. The finish
tempered oilfield component may then undergo supplemental
age-hardening to further strengthen the clad material without
further tempering the base material.
[0094] Supplemental age-hardening may also be performed on a
conventionally quenched and final-tempered oilfield component.
Castings, forgings, and pressings used in oilfield components may
be fully heat-treated by processes including normalizing,
austenitizing, solution annealing, tempering, age-hardening, heat
treating, and other methods as known in the art to achieve the
desired final base material properties before they are inlaid or
overlaid with CRA material. The conventionally quenched and
final-tempered oilfield component may then be supplementally aged
to further strengthen the clad material without affecting the
"final" temper.
[0095] During supplemental age-hardening, at least a portion of the
oilfield component may be actively cooled, thereby maintaining the
base material at a temperature less than a tempering temperature of
the base material. As used herein, "active cooling" may include
conductive cooling, forced convective cooling, heat exchange with a
medium such as a moving fluid (vapor or liquid), spray cooling
(e.g., a water spray on a portion of the surface), or other means
of cooling known to those of skill in the art, exclusive of natural
convective or still-air cooling. Active cooling may be used, for
instance, where the age-hardening temperature of the clad material
exceeds the tempering temperature of the base material.
[0096] In some embodiments, the base material may remain at least
50.degree. F. below a tempering temperature of the base material
during the selective age-hardening of the clad material; at least
75.degree. F. below in other embodiments; and at least 100.degree.
F. below in other embodiments.
[0097] Additionally, selective reinforcement of an oilfield
component may not result in a uniform thickness of clad material
over an entire surface. In some embodiments, the thickness of the
clad material may vary. For example, as illustrated in FIG. 3A, a
selective reinforcement may be applied where a portion of the clad
material 30 is thick, tapering off to a minimal thickness at a
surface interface 32 of the base material 34 with the clad material
30. In other embodiments, a selective reinforcement may be applied
where the clad material 30 has a uniform or nearly uniform
thickness, even at the interface 32 with base material 34, as
illustrated in FIG. 3B.
[0098] Where the clad material is supplementally aged, selectively
heating the entire surface of the clad material may result in the
base material, at or near the interface 32, exceeding the tempering
temperature of the base material. To avoid exceeding the tempering
temperature of the base material at or near the interface,
supplemental age-hardening may include the selective heating of
only a portion of the clad inlay. For example, as illustrated in
FIG. 3B, the central portion 36 of clad inlay 30 may be selectively
heated, where conduction may age-harden the outer portions of the
clad material 30 while maintaining the temperature of the base
material 34 at or near interface 32 below a tempering temperature
of the base material 34. In this manner, the base material 34, even
at the interface 32 with clad material 30, may remain at a hardness
of Brinell 237 or less.
[0099] Referring now to FIGS. 4A and 4B, results of FEA simulations
performed to investigate the differences between active cooling and
still-air cooling of a clad inlay during a supplemental
age-hardening process are shown. In this example, FEA simulations
were performed on a 12 inch thick, 19 inch inner diameter cylinder
of F22 having a clad inlay of 0.5 inch INCONEL 725 applied to its
inner diameter. To simplify the model, a uniform inlay thickness
was assumed. The surface of the clad inlay was set at 1350.degree.
F., and the temperature of the outer surface of the cylinder was
varied based upon active cooling and still-air cooling.
[0100] As shown in FIGS. 4A and 4B, still-air cooling may result in
an outer wall temperature of about 800.degree. F., whereas active
cooling may maintain the outer wall temperature as low as
75.degree. F. More importantly, active cooling may maintain the
base material, at the interface with the clad material (0.5 inch
depth), at a temperature less than the tempering temperature of the
base material, 1180.degree. F. In contrast, still-air cooling
resulted in the base material exceeding the tempering temperature.
These simulation results indicate that active cooling may provide a
method to supplementally age harden a clad inlay, while maintaining
the base material at a temperature below the tempering temperature
of the base material.
[0101] In selected embodiments, during supplemental age-hardening,
at least a portion of the clad material may be selectively heated
to a temperature between about 1250.degree. F. and 1400.degree. F.
In some embodiments, during supplemental age-hardening, at least a
portion of a surface of the oilfield component may be maintained at
a temperature of 250.degree. F. or less; 200.degree. F. or less in
other embodiments; 150.degree. F. or less in other embodiments;
100.degree. F. or less in other embodiments; 75.degree. F. or less
in other embodiments; and 50.degree. F. or less in yet other
embodiments.
[0102] Exemplary Embodiments
[0103] The prior art manufacturing process described above may be
modified in accordance with the present disclosure as follows. The
ram BOP body may be forged and rough machined in the same manner as
is presently done, however the heat treatment of the rough machined
BOP body would be modified. The body would still be normalized and
austenitized at the appropriate temperatures and liquid quenched as
is the present practice. After the completion of the liquid quench,
the temper would be modified to a much lower value, and a "snap" or
intermediate low temperature temper would be performed. As
previously discussed, one purpose of the snap temper is to prevent
spontaneous or "autogenous" cracking of the as quenched low-alloy
steel material during processing until the time of the final
temper.
[0104] Upon receipt of the rough machined and snap-temper heat
treated forging, the BOP body may be prepared for weld overlay. The
BOP body may then be overlay welded to selectively reinforce those
areas determined by the stress analysis described above, which may
be transferred to the engineering drawing. After all welding has
been completed, the BOP body may be charged to the tempering
furnace for finish tempering, a combination heat treatment of the
weldment joint of the overlay clad material on the low-alloy steel
substrate.
[0105] The finish temper would consist of a temper for the base
metal to develop the mechanical properties required of the base
metal by the material specification. The temper would also provide
for the PWHT of the HAZ of the weldment joint since the
tempering/aging temperature would be above the PWHT temperature
normally used for the base material/CRA weldment joint. And lastly
the temper would serve as the age hardening heat treatment for the
high strength CRA overlay filler metal.
[0106] This finish temper process is possible since the tempering
temperature of the base metal and the aging temperature of the CRA
overlay material may be nearly identical, such as when the base
material and CRA overlay are properly selected and processed. The
time required by both the tempering cycle and the age hardening
cycle are such that they may be averaged and achieve the properties
required of both materials.
[0107] The mechanical properties of the alloy may be determined by
use of a separate qualification test coupon, QTC, which may be heat
treated separately from the part itself provided that it is heat
treated according to specific rules mandated by API for parts to be
used in the oil exploration and production industry. For example,
to verify that the BOP body conforms to the material property
requirements, two qualification test coupons, QTCs, may be produced
from the same heat of steel from which the BOP body is produced.
The two qualification test coupons, QTCs, from the same heat of the
low-alloy steel from which the body was forged, may be normalized,
austenitized, liquid quenched and tempered either simultaneously
with or separately from the body forging using the same cycle
temperatures and times. One of the QTCs may be tempered at a
temperature and time necessary to develop the mechanical properties
required by the material specification. The remaining QTC may be
finish tempered along with the selectively reinforced BOP. These
QTCs may then be sent to a mechanical testing laboratory for
mechanical testing of the mechanical properties to ensure that the
base material and the clad material meet the specified
requirements.
[0108] Finish tempering the BOP body in this manner may allow the
base material and the clad material to meet the desired properties,
including yield strength, hardness, and/or the requirements of NACE
for resistance to stress corrosion cracking. Moreover, the CRA
inlays should be more resistant to and help reduce axial or bending
fatigue failures.
[0109] For example, Grade F22 forgings or castings may be produced
and machined in the manner is which they have normally been
produced, as described above. However, the heat treatment may be
modified. The normalizing and austenitizing temperature cycles and
times along with the liquid quench may remain unchanged. The
tempering temperature may be changed to between 900.degree. F.
(482.degree. C.) and 1100.degree. F. (593.degree. C.) and the time
at temperature may be reduced or remain unchanged. The forged BOP
body may then be selectively reinforced with INCONEL 725 or another
age hardenable alloy or CRA.
[0110] Once the welding operations are complete, the selectively
reinforced BOP body may be charged to a heat treating furnace to
perform a finish temper that may be a combination temper, aging,
and PWHT, to stress relief anneal the HAZ of the Grade F22 base
metal and age harden the INCONEL 725 CRA weld metal inlay and
develop the mechanical properties of the Grade F22 forging. Other
age hardenable alloys and/or CRAs, such as, INCONEL 718 SPF (Alloy
718), may also be used as the filler metal for this application.
The temperature and time of the finish temper (combination
temper/PWHT/age hardening heat treatment) step may be determined by
the weld procedure qualification record ("PQR") and documented on
the weld procedure specification ("WPS"). After the finish temper
has been completed, a similarly processed QTC may be delivered to a
metallurgical testing laboratory for the determination of the
mechanical properties of the material and whether they meet the
requirements of the material specification.
[0111] Since the PWHT and the tempering cycle may be performed
simultaneously with the age hardening of the clad inlay metal,
there will not be any loss of mechanical properties of the base
metal as may occur where a separate PWHT is performed after the
temper of the low-alloy steel base metal.
[0112] In an exemplary embodiment, a ram BOP body forging is
produced from F22 alloy. The raw forging is normalized at
1750.degree. F. for 30 minutes per inch of CST "dwell" time, plus
one hour "soak" time. It is then water quenched and snap-tempered
at 900.degree. F. for 30 minutes per inch of CST, plus one
hour.
[0113] Optionally, the quenched and snap-tempered ram BOP body is
then rough machined, for example with "weld necks" to facilitate
welding flanges to the BOP body. Optionally, various appurtenances
such as flange connection or fixtures are then welded to the
Q&ST body; these appurtenances may preferably also be comprised
of Q&ST F22 alloy. The Q&ST body is then finished-machined
and inlaid with INCONEL 725 in areas requiring selective
reinforcement and/or improved corrosion resistance. Optionally, the
inlaid areas are further machined. Finally, the finish-machined
body with inlay reinforcement is "finish tempered" at 1220.degree.
F. for a "dwell" time of about 40-42 minutes per inch of CST, plus
a "soak" time of one hour. Following this procedure, the yield
strength of the F22 base material will be about 85,000 psi, and the
yield strength of the inlaid INCONEL 725 will be greater than
115,000 psi. Additionally, the finish tempering process will also
serve to relieve the residual stresses in the heat-affected zones
of the welds, so there is no need for supplemental PWHT.
[0114] In another exemplary embodiment, an annular BOP body may be
fabricated from ring forgings of 8630 Modified which have been
quenched and snap-tempered to about 900.degree. F. at 30 minutes
per inch of critical section "dwell" time plus one hour "soak"
time. The Q&ST rings may be stacked together and
full-penetration welded end-to-end. The welded stack of Q&ST
rings may be machined and selectively reinforced with INCONEL 725
weld inlay material, then finish tempered at about 1260.degree. F.
for a dwell time of about 30-45 minutes per inch of CST dwell time,
plus a soak time of about one hour.
[0115] Embodiments and methods disclosed herein may advantageously
provide for generating and analyzing oilfield component models with
FEA using stress and/or fatigue analysis to determine the
component's response under fatigue loading conditions characterized
by large amounts of stress. The resulting analysis may then be used
to enhance component design, improving the performance of the
component under fatigue loading conditions.
[0116] Advantageously, embodiments disclosed herein may provide a
method to establish an overall oilfield component design based on
ASME Section-VIII Div-3 or similar high-pressure, high-temperature
equipment design guidelines. The component may satisfy NACE peak
stress and life cycle requirements. Methods and embodiments
disclosed herein may provide for oilfield components with an
increased working lifespan. For example, the oilfield component may
be modeled with simulated fatigue loading conditions of repeated
compression, bending, etc., to determine design features that may
extend the working lifespan of the oilfield component.
[0117] Advantageously, embodiments disclosed herein may provide a
method to manufacture oilfield components that is less costly than
attempting to manufacture the component from a solid, high strength
corrosion resistant alloy or other metal that may meet the
requirements of NACE MR0175. This is especially true in view of the
fact that the mechanical strength of the body beneath the clad
layer 0.250 to 0.500 inches from the well bore fluid wetted
surfaces may be much lower that that required within that localized
zones subject to fatigue failure. Other embodiments may provide for
the enhancement of existing component designs so that sulfide
stress corrosion cracking or corrosion related limit conditions may
be met by selectively reinforcing the oilfield component with
higher strength material suitable for use in an oil and gas
environment.
[0118] The selection of the cladding alloy may be based on the
increased mechanical strength of the clad layer and may also be
based on the metallurgical bond achieved between the clad layer and
the substrate. An additional attribute of the clad layer may be the
corrosion resistance that the cladding alloy may contribute to the
oilfield component. Another attribute of the clad layer is that any
scoring or gouging of the interior surface of the component is not
likely to extend below the depth of the clad layer, thus allowing
the clad layer to continue to protect the low-alloy steel substrate
on which it is deposited. Particularly, the clad layer may also
continue to protect the component from pitting corrosion often
found in the cavities of oilfield components. Moreover, the repair
of gouges in the clad layer may be easier and less costly to
perform than the repair of similar damage to the low-alloy steel
substrate.
[0119] In other aspects, embodiments disclosed herein may
advantageously provide for a method to manufacture selectively
reinforced oilfield components. The method may include finish
tempering the oilfield component at a selected time and temperature
to temper the base material and age harden the clad material used
to form the selectively reinforced oilfield component. In this
manner, the method may advantageously provide for developing the
required properties of the base material, post-weld heat treatment
of the weldment joint adjoining the base material and the clad
material, and age hardening the clad material.
[0120] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
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