U.S. patent application number 11/435627 was filed with the patent office on 2007-11-22 for method for making high-strength steel pipe, and pipe made by that method.
This patent application is currently assigned to IPSCO Enterprises, Inc.. Invention is credited to Steven S. Hansen, Joseph D. Russo.
Application Number | 20070267110 11/435627 |
Document ID | / |
Family ID | 38686923 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070267110 |
Kind Code |
A1 |
Hansen; Steven S. ; et
al. |
November 22, 2007 |
Method for making high-strength steel pipe, and pipe made by that
method
Abstract
A method is provided for manufacturing a high-strength,
as-welded steel pipe product, with a minimum yield strength in
excess of 80 ksi (552 MPa), suitable for use in oil and gas well
casings, without the need for a post-weld heat treatment which
would otherwise be required to obtain an as-welded pipe having that
level of strength.
Inventors: |
Hansen; Steven S.;
(Fairhope, AL) ; Russo; Joseph D.; (Aurora,
IL) |
Correspondence
Address: |
GREENBERG TRAURIG, LLP
77 WEST WACKER DRIVE, SUITE 2500
CHICAGO
IL
60601-1732
US
|
Assignee: |
IPSCO Enterprises, Inc.
|
Family ID: |
38686923 |
Appl. No.: |
11/435627 |
Filed: |
May 17, 2006 |
Current U.S.
Class: |
148/546 ;
148/593; 420/110 |
Current CPC
Class: |
C22C 38/02 20130101;
C21D 8/10 20130101; C22C 38/26 20130101; C22C 38/38 20130101; C21D
8/105 20130101; C22C 38/22 20130101 |
Class at
Publication: |
148/546 ;
148/593; 420/110 |
International
Class: |
C21D 8/10 20060101
C21D008/10; C22C 38/22 20060101 C22C038/22 |
Claims
1. A method for making an as-welded steel pipe, comprising the
steps of: forming a cast steel slab, the steel having as components
(i) less than about 0.10% by weight of carbon, (ii) an Mn content
in the range of about 1.5% to about 2.5% by weight, (iii) at least
one of Mo, Cr, Ni, and B, and (iv) at least one of Nb, V, and Ti;
heating the steel slab to a temperature in excess of about
2000.degree. F.; rolling the heated steel slab in a rolling mill at
a temperature in excess of the Ar.sub.3 transformation start
temperature, to obtain a skelp having a desired thickness; cooling
the skelp to a coiling temperature in the range of about
850.degree. F. to about 950.degree. F., to obtain a largely
bainitic microstructure in the skelp; coiling the skelp into a
hot-rolled coil; forming the skelp into a tube such that the two
side edges of the skelp are positioned into contact with one
another; and welding the two side edges of the skelp together so as
to form the as-welded pipe.
2. The method according to claim 1, wherein the steel contains
carbon in an amount of from about 0.040% to about 0.060% by
weight.
3. The method according to claim 2, wherein the steel contains
carbon in an amount of from about 0.040% to about 0.055% by
weight.
4. The method according to claim 2, wherein the steel contains
carbon in an amount of from about 0.045% to about 0.060% by
weight.
5. The method according to claim 1, wherein the steel contains Mn
in an amount of from about 1.5% to about 2.5% by weight.
6. The method according to claim 5, wherein the steel contains Mn
in an amount of from about 1.65% to about 1.75% by weight.
7. The method according to claim 5, wherein the steel contains Mn
in an amount of from about 1.80% to about 1.90% by weight.
8. The method according to claim 1, wherein the steel contains at
least one of Mo in an amount of from about 0.10% to about 0.50% by
weight, Cr in an amount of about 0.50% or less by weight, Ni in an
amount of about 0.50% or less by weight and B in an amount of from
about 0.0005% to about 0.0030% by weight.
9. The method according to claim 8, wherein the steel contains Mo
in an amount of from about 0.28% to about 0.32% by weight.
10. The method according to claim 8, wherein the steel contains Cr
in an amount of from about 0.15% to about 0.20% by weight.
11. The method according to claim 1, wherein the steel contains Nb
in an amount of from about 0.040% to about 0.050% by weight.
12. The method according to claim 1, wherein the steel contains Nb
in an amount of from about 0.075% to about 0.085% by weight.
13. The method according to claim 1, wherein the steel contains Ti
in an amount of from about 0.008% to about 0.015% by weight.
14. The method according to claim 1, wherein the steel contains Ti
in an amount of from about 0.015% to about 0.025% by weight.
15. The method according to claim 1, wherein the steel contains V
in an amount of from about 0.05% to about 0.06% by weight.
16. The method according to claim 1, wherein the steel contains
carbon in an amount of from about 0.040% to about 0.055% by weight;
Mn in an amount of from about 1.82% to about 1.90% by weight; Si in
an amount of from about 0.26% to about 0.34% by weight; Al in an
amount of from about 0.022% to about 0.035% by weight; Cr in an
amount of from about 0.15% to about 0.20% by weight; Mo in an
amount of from about 0.29% to about 0.32% by weight; Nb in an
amount of from about 0.075% to about 0.085% by weight; and Ti in an
amount of from about 0.015% to about 0.025% by weight.
17. The method according to claim 1, wherein the steel contains
carbon in an amount of from about 0.045% to about 0.060% by weight;
Mn in an amount of from about 1.65% to about 1.75% by weight; Si in
an amount of from about 0.12% to about 0.18% by weight; Al in an
amount of from about 0.015% to about 0.025% by weight; Cr in an
amount of from about 0.15% to about 0.20% by weight; Mo in an
amount of from about 0.28% to about 0.32% by weight; Nb in an
amount of from about 0.040% to about 0.050% by weight; Ti in an
amount of from about 0.008% to about 0.015% by weight; and V in an
amount of from about 0.05% to about 0.06% by weight.
18. The method according to claim 1, wherein the steel contains
carbon in an amount of from about 0.075% to about 0.080% by weight;
Mn in an amount of from about 1.82% to about 1.90% by weight; Si in
an amount of from about 0.26% to about 0.34% by weight; Al in an
amount of from about 0.019% to about 0.025% by weight; Cr in an
amount of from about 0.15% to about 0.20% by weight; Mo in an
amount of from about 0.29% to about 0.32% by weight; Nb in an
amount of from about 0.075% to about 0.085% by weight; and Ti in an
amount of from about 0.015% to about 0.025% by weight.
19. The method according to claim 1, wherein the steel slab is
heated to a temperature of about 2300.degree. F.
20. The method according to claim 1, wherein the heated steel slab
is rolled at a temperature of about 1500.degree. F.
21. The method according to claim 1, wherein the skelp is slit
longitudinally to form a plurality of slit strips, each of said
strips then being formed into a tube.
22. The method according to claim 1, wherein the welding method
comprises electric resistance welding.
23. A steel pipe formed by the method of any of claims 1, 16, 17 or
18.
24. The steel pipe of claim 23, wherein the pipe has a minimum
yield strength in excess of about 80 ksi (552 MPa).
25. The steel pipe of claim 23, wherein the pipe has a minimum
yield strength in the range of from about 80 ksi (552 MPa) to about
125 ksi (862 MPa).
26. The steel pipe of claim 23, wherein the pipe has a minimum
yield strength in excess of about 100 ksi (689 MPa).
27. The steel pipe of claim 23, wherein the diameter of the pipe is
at least about 4.5 inches.
28. The steel pipe of claim 23, wherein the wall thickness of the
pipe is at least about 0.25 inches.
29. An as-welded steel pipe having a minimum yield strength in
excess of about 80 ksi (552 MPa), wherein said minimum yield
strength is obtained without the use of a post-formation quench and
temper heat treatment.
30. The steel pipe of claim 29, wherein the pipe has a minimum
yield strength in the range of from about 80 ksi (552 MPa) to about
125 ksi (862 MPa).
31. The steel pipe of claim 29, wherein the pipe has a minimum
yield strength in excess of about 100 ksi (689 MPa).
32. The steel pipe of claim 29, wherein the diameter of the pipe is
at least about 4.5 inches.
33. The steel pipe of claim 29, wherein the wall thickness of the
pipe is at least about 0.25 inches.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
REFERENCE TO A "MICROFICHE APPENDIX"
[0003] Not Applicable.
BACKGROUND OF THE DISCLOSURE
[0004] 1. The Technical Field
[0005] The present invention relates to a method for manufacturing
a high-strength, as-welded steel pipe product, with a minimum yield
strength in excess of 80 ksi (552 MPa), suitable for use in oil and
gas well casings, without the need for a post-weld heat treatment
which would otherwise be required to obtain an as-welded pipe
having that level of strength.
[0006] 2. The Prior Art
[0007] In the oil and gas industry, the strength and durability of
the steel pipe used for oil and gas well casings is crucial to the
efficiency and productivity of the oil and gas recovery efforts.
The commercial market for such steel pipe products is commonly
referred to as the Oil Country Tubular Goods (OCTG) market. Typical
dimensions for pipe used in such casing products are (i) an outside
diameter greater than 4.5 inches; and (ii) a wall thickness greater
than 0.205 inches. Steel casing is typically used to line an oil or
gas well, to enable extraction of the oil or gas therefrom.
[0008] In the OCTG market, two types of pipe are conventionally
utilized for casings: (i) welded pipe formed from hot-rolled steel
(skelp) which has been turned and fashioned into a tube, having a
straight longitudinal weld (also referred to as "as-welded" or
"as-rolled" pipe); and (ii) seamless pipe produced by subjecting a
cast billet to a piercing operation followed by a stretch-forming
operation (also referred to as "as-formed" pipe). Each type of
casing has its own relatively distinct set of structural
characteristics, which are a function of the steel alloy and the
respective steel processing techniques and pipe formation
methods.
[0009] Typically, as-welded casing products are formed from medium
carbon (0.15% to 0.30% C) grade steel which is hot-rolled to yield
a suitable pipe skelp, and then formed and welded into pipe through
the use of conventional pipe formation techniques, preferably
through the use of electric resistance welding (ERW) to form the
pipe seam. The strength level of the casing typically depends on a
number of factors, including (i) the composition of the steel
utilized; (ii) the processing steps used to manufacture the skelp;
and (iii) the process through which the pipe is formed, welded and
sized. With regard to the composition of the steel, the use of
small amounts of niobium (or columbium) (Nb), vanadium (V) and
titanium (Ti) (singly or in combination) is known to increase the
strength of both the skelp and the pipe formed therefrom.
[0010] In the conventional method for producing the skelp utilized
in forming as-welded casing products, a cast steel slab having the
desired composition is heated to a temperature of approximately
2300.degree. F., and then hot-rolled in a rolling mill at a
temperature of approximately 1500.degree. F., to obtain a skelp
having the desired thickness. The skelp is then cooled with water
to a coiling temperature in the range of 1100.degree. F. to
1200.degree. F., so as to produce a microstructure which is largely
a mixture of ferrite and pearlite (referred to hereinbelow as
"ferrite+pearlite"). The cooled skelp is then typically coiled up
for ease in handling, transport and storage.
[0011] In order to form the pipe, the skelp is initially slit
longitudinally to a width which corresponds to the desired
circumference of the pipe. The slit skelp is then passed
progressively through a series of rolls to form the skelp into a
round tube. The edges of the slit are then welded together,
preferably using an electric resistance welding (ERW) process, to
form a longitudinal weld seam. The use of ERW processes is
well-known in the art of tube and pipe production.
[0012] As-welded steel casing products with minimum yield strength
levels ranging from 40 ksi (276 MPa) to 80 ksi (552 MPa) are
well-known in the OCTG industry. Examples of such as-welded casing
products include the API H40 and J55 industry specifications, as
well as proprietary Grade 80 casing products. However, recent
increases in oil and gas exploration in North America have led to
the development of deeper wells, which typically require
higher-strength grade casings in order to operate efficiently. This
has led to an increased demand for OCTG casings having minimum
yield strengths substantially in excess of 80 ksi (552 MPa).
[0013] In order to produce casing products having a minimum yield
strength greater than 80 ksi (552 MPa), conventional technology has
utilized a so-called "quench and temper" heat treatment, in which
the as-welded or as-formed pipe, having a predominantly
ferrite+pearlite microstructure, is heated above the A.sub.3
temperature (into the austenite phase field) to approximately
1650.degree. F. to 1750.degree. F., water quenched to ambient and
then tempered by reheating into the temperature range of
900.degree. F. to 1300.degree. F. The steel grades used in
producing heat-treated casing products typically include 0.20 to
0.30% carbon (C), with sufficient additions of manganese (Mn),
molybdenum (Mo), nickel (Ni), chromium (Cr) and/or boron (B), so as
to produce a predominantly martensitic microstructure on quenching.
The tempering heat treatment results in a tempered martensitic
microstructure, in which the high as-quenched yield strength is
reduced to the lower, desired range.
[0014] Heat-treated casing products with minimum yield strength
levels ranging up to 125 ksi (862 MPa) are well-known in the OCTG
industry. Examples of such heat-treated casing products include
industry specifications such as API L80, P110 and Q125 grade casing
products.
[0015] However, the use of post-weld heat treatment to obtain a
casing product having the desired minimum yield strength in the
range of 80 ksi (552 MPa) to 125 ksi (862 MPa) adds additional cost
to the pipe manufacturing process, both in the form of additional
capital costs associated with the equipment needed for the heat
treatment process, additional energy costs associated with the use
of such equipment and additional production costs associated with
the additional time and labor required for heat treatment.
[0016] It is well-known that bainitic microstructures demonstrate
increased hardness and strength when compared to the
ferrite+pearlite microstructures found in conventional as-welded
casing products. The higher strength of the steel is of great
importance in the oil and gas industry as the wells have gotten
deeper and require higher-strength casings.
[0017] Additionally, compared to heat-treated grades, bainitic
steels demonstrate improved weldability due to their generally
lower carbon contents. While many metals and thermoplastics can be
welded, some are easier to weld than others. Weldability greatly
influences weld quality and is an important factor in choosing
which welding process to use. The lower carbon concentration of
bainitic steels enables those steels to be welded easier, while
also maintaining better (higher) ductility and toughness than
ferrite+pearlite steels.
[0018] Thus, it would be desirable to provide a process for
manufacturing an as-welded steel casing product having a bainitic
microstructure, yielding a minimum yield strength in the range of
80 ksi (552 MPa) to 125 ksi (862 MPa), without the need for a
post-formation heat treatment step. It would be highly desirable to
provide such a process which yields an as-welded steel casing
product having a minimum yield strength in excess of 100 ksi (689
MPa)--a strength level heretofore typically achievable only through
the use of heat treatment after pipe formation.
[0019] These and other desirable characteristics of the invention
will become apparent in view of the present specification,
including the claims, and drawings.
SUMMARY OF THE INVENTION
[0020] The invention comprises a method for making an as-welded
steel pipe, comprising the steps of
[0021] forming a cast steel slab, the steel having as
components
[0022] (i) less than about 0.10% by weight of carbon,
[0023] (ii) an Mn content in the range of about 1.5% to about 2.5%
by weight,
[0024] (iii) at least one of Mo, Cr, Ni and B, and
[0025] (iv) at least one of Nb, V, and Ti;
[0026] heating the steel slab to a temperature in excess of about
2000.degree. F.;
[0027] rolling the heated steel slab in a rolling mill at a
temperature in excess of the Ar.sub.3 transformation start
temperature, to obtain a skelp having a desired thickness;
[0028] cooling the skelp to a coiling temperature in the range of
about 850.degree. F. to about 950.degree. F., to obtain a largely
bainitic microstructure in the skelp;
[0029] coiling the skelp into a hot-rolled coil;
[0030] forming the skelp into a tube such that the two side edges
of the skelp are positioned into contact with one another; and
[0031] welding the two side edges of the skelp together so as to
form the as-welded pipe.
[0032] Preferably, the steel utilized in making pipe according to
the invention contains carbon in an amount of from about 0.040% to
about 0.060% by weight. In one preferred embodiment of the
invention, the steel contains carbon in an amount of from about
0.040% to about 0.055% by weight. In another preferred embodiment
of the invention, the steel contains carbon in an amount of from
about 0.045% to about 0.060% by weight.
[0033] Additionally, the steel preferably contains Mn in an amount
of from about 1.5% to about 2.5% by weight. In one preferred
embodiment of the invention, the steel contains Mn in an amount of
from about 1.65% to about 1.75% by weight. In another preferred
embodiment of the invention, the steel contains Mn in an amount of
from about 1.80% to about 1.90% by weight.
[0034] The steel also preferably contains at least one of Mo in an
amount of from about 0.10% to about 0.50% by weight, Cr in an
amount of about 0.50% or less by weight, Ni in an amount of about
0.50% or less by weight and B in an amount of from about 0.0005% to
about 0.0030% by weight. In one preferred embodiment of the
invention, the steel contains at least one of Mo in an amount of
from about 0.28% to about 0.32% by weight, Cr in an amount of from
about 0.15% to about 0.20% by weight, and Nb in an amount of from
about 0.040% to about 0.050% by weight. In another preferred
embodiment of the invention, the steel contains Nb in an amount of
from about 0.075% to about 0.085% by weight.
[0035] In one preferred embodiment of the invention, the steel
contains Ti in an amount of from about 0.008% to about 0.015% by
weight. In another preferred embodiment of the invention, the steel
contains Ti in an amount of from about 0.015% to about 0.025% by
weight. In yet another preferred embodiment of the invention, the
steel contains V in an amount of from about 0.05% to about 0.06% by
weight. In one highly preferred embodiment of the invention, the
steel contains:
[0036] carbon in an amount of from about 0.040% to about 0.055% by
weight;
[0037] Mn in an amount of from about 1.82% to about 1.90% by
weight;
[0038] Si in an amount of from about 0.26% to about 0.34% by
weight;
[0039] Al in an amount of from about 0.022% to about 0.035% by
weight;
[0040] Cr in an amount of from about 0.15% to about 0.20% by
weight;
[0041] Mo in an amount of from about 0.29% to about 0.32% by
weight;
[0042] Nb in an amount of from about 0.075% to about 0.085% by
weight; and
[0043] Ti in an amount of from about 0.015% to about 0.025% by
weight.
In another highly preferred embodiment of the invention, the steel
contains
[0044] carbon in an amount of from about 0.045% to about 0.060% by
weight;
[0045] Mn in an amount of from about 1.65% to about 1.75% by
weight;
[0046] Si in an amount of from about 0.12% to about 0.18% by
weight;
[0047] Al in an amount of from about 0.015% to about 0.025% by
weight;
[0048] Cr in an amount of from about 0.15% to about 0.20% by
weight;
[0049] Mo in an amount of from about 0.28% to about 0.32% by
weight;
[0050] Nb in an amount of from about 0.040% to about 0.050% by
weight;
[0051] Ti in an amount of from about 0.008% to about 0.015% by
weight; and
[0052] V in an amount of from about 0.05% to about 0.06% by
weight.
In still another highly preferred embodiment of the invention, the
steel contains
[0053] carbon in an amount of from about 0.075% to about 0.080% by
weight;
[0054] Mn in an amount of from about 1.82% to about 1.90% by
weight;
[0055] Si in an amount of from about 0.26% to about 0.34% by
weight;
[0056] Al in an amount of from about 0.019% to about 0.025% by
weight;
[0057] Cr in an amount of from about 0.15% to about 0.20% by
weight;
[0058] Mo in an amount of from about 0.29% to about 0.32% by
weight;
[0059] Nb in an amount of from about 0.075% to about 0.085% by
weight; and
[0060] Ti in an amount of from about 0.015% to about 0.025% by
weight.
[0061] In one preferred embodiment of the invention, the steel slab
is heated to a temperature of about 2300.degree. F., and the heated
steel slab is then rolled at a temperature of about 1500.degree.
F.
[0062] In a preferred embodiment of the invention, the skelp is
slit longitudinally to form a plurality of slit strips, each of
said strips then being formed into a tube. In another preferred
embodiment of the invention, the welding method comprises electric
resistance welding.
[0063] The invention also comprises a steel pipe formed by any of
the methods described above. In one preferred embodiment of the
invention, the pipe has a minimum yield strength in excess of about
80 ksi (552 MPa). In another preferred embodiment of the invention,
the pipe has a minimum yield strength in the range of from about 80
ksi (552 MPa) to about 125 ksi (862 MPa). In one such highly
preferred embodiment of the invention, the pipe has a minimum yield
strength in excess of about 100 ksi (689 MPa). Preferably, the
diameter of the pipe is at least about 4.5 inches, and the wall
thickness of the pipe is at least about 0.205 inches.
[0064] The invention further comprises an as-welded steel pipe
having a minimum yield strength in excess of about 80 ksi (552
MPa), wherein said minimum yield strength is obtained without the
use of a post-formation quench and temper heat treatment. In a
preferred embodiment of the invention, the pipe has a minimum yield
strength in the range of from about 80 ksi (552 MPa) to about 125
ksi (862 MPa). In a highly preferred embodiment of the invention,
the pipe has a minimum yield strength in excess of about 100 ksi
(689 MPa). Preferably, the diameter of the pipe is at least about
4.5 inches, and the wall thickness of the pipe is at least about
0.205 inches.
BRIEF DESCRIPTION OF THE DRAWINGS
[0065] FIG. 1 is a schematic diagram showing the steps by which a
cast steel slab is hot-rolled and coiled to form a skelp for use in
the pipe forming process;
[0066] FIG. 2A is a schematic illustration of the pipe forming
process, showing slit skelp entering the formation equipment;
[0067] FIG. 2B is a sectional view of the slit skelp, taken at the
position indicated in FIG. 2A, and looking in the direction of the
arrows 2B-2B;
[0068] FIG. 3A is a schematic illustration of the pipe forming
process, showing slit skelp after having been rolled into a tubular
shape, but prior to welding;
[0069] FIG. 3B is a sectional view of the slit skelp in
perspective, taken at the position indicated in FIG. 3A, and
looking in the direction of the arrows 3B-3B;
[0070] FIG. 4A is a schematic illustration of the pipe forming
process, showing slit skelp after having been rolled into a tubular
shape, and after welding; and
[0071] FIG. 4B is a sectional view of the slit skelp in
perspective, taken at the position indicated in FIG. 4A, and
looking in the direction of the arrows 4B-4B.
DETAILED DESCRIPTION OF THE INVENTION
[0072] While this invention is susceptible of embodiment in many
different forms, there is shown in the drawings and will herein be
described in detail, several preferred embodiments, with the
understanding that the present disclosure should be considered as
an exemplification of the principles of the invention and is not
intended to limit the invention to the embodiments so
illustrated.
[0073] When making reference to percentages of compositional
components, it is to be understood that, unless otherwise
specified, the percentage given is by weight of the total
alloy.
[0074] As indicated hereinabove, the present invention is directed
to a steel composition and processing method used in producing an
as-welded tubular steel product, and particularly a casing product
for the OCTG market, having a minimum yield strength in the range
of 80 ksi (552 MPa) to 125 ksi (862 MPa). Preferably, the invention
is directed to a steel composition and processing method used in
producing an as-welded tubular steel product having a minimum yield
strength in excess of 100 ksi (689 MPa), and a minimum ultimate
tensile strength in excess of 110 ksi (758 MPa).
[0075] This invention employs a controlled steel composition and
steel processing procedure that produces a skelp having the desired
bainitic microstructure and properties, such that the subsequent
pipe formation process of forming, welding and sizing hardens the
material to the desired strength level. By producing a skelp having
a bainitic microstructure, the invention provides a steel pipe
which is not only stronger than known as-welded pipe products
having a predominantly ferrite+pearlite microstructure, but also
exhibits increased weldability and formability when compared to
other such products.
[0076] While a preferred use of the steel pipe made according to
the invention is for oil and gas well casings used in the OCTG
market, the scope of the invention is not limited to that
particular use. Rather, the steel pipe of the invention is suitable
for use in any application for which a steel pipe having a yield
strength in excess of 80 ksi (552 MPa) is desirable.
[0077] An important feature of the present invention is the
composition of the steel used in forming the skelp. Use of the
proper steel composition is believed to be important in achieving
the benefits of the invention, namely, an as-welded pipe having a
bainitic microstructure which provides a minimum yield strength in
the range of 80 ksi (552 MPa) to 125 ksi (862 MPa). The key
compositional parameters considered to be important to the
invention are: (i) a low carbon content of less than 0.10%, to
maintain a good level of formability and weldability in the skelp;
(ii) a Mn content in the range of 1.5% to 2.5%, to help produce the
desired as-rolled bainitic microstructure; (iii) the addition of Mo
(0.10% to 0.50%), Cr (up to 0.50%), Ni (up to 0.50%) and/or B
(0.0003% to 0.0030%) to help produce the desired as-rolled bainitic
microstructure, and (iv) the addition of Nb, V and Ti, singly or in
combination, to increase the strength of the as-rolled skelp.
[0078] The component percentages of the preferred steel composition
can be adjusted upwardly or downwardly, depending upon the pipe
strength level that is desired in a given application. For example,
an increase in the pipe strength will be expected as carbon,
manganese, molybdenum, chromium and/or nickel levels are increased.
This is due to the effect of these elements in reducing the
transformation temperature range. Additionally, increasing the
niobium (columbium) content will be expected to increase the
strength of the steel due to increased precipitation
strengthening.
[0079] The use of each of these elements as an additive in a steel
composition, in order to achieve these desired properties, is
well-known in the art of steel processing; however, the use of the
particular combinations of those elements described herein, in
combination with the specific processing steps described
hereinbelow, is believed to be novel and non-obvious.
[0080] While the processing of the skelp utilized in forming the
casing products of the invention is similar to conventional steel
processing procedures used in manufacturing steel skelp for forming
as-welded pipe products for the OCTG market, as described above,
certain departures from the conventional procedures are required in
order to achieve the benefits of the invention. Specifically, it is
believed that the temperature of the skelp must be carefully
controlled during the coiling process, within the range of
850.degree. F. to 950.degree. F., in order to achieve the desired
bainitic microstructure in the skelp, which enables the manufacture
of an as-welded pipe having the desired minimum yield strength in
excess of 80 ksi (552 MPa).
[0081] The processing procedure utilized in connection with the
invention is illustrated in FIG. 1. First, a cast steel slab 4
having the desired composition is heated in a slab reheat furnace 5
to a temperature of approximately 2300.degree. F., and then
hot-rolled in a rolling mill 6, over a temperature range of
approximately 2000.degree. F. to 1500.degree. F., to obtain skelp
having the desired thickness. Typical thicknesses for casing
utilized in the OCTG market are in the range of from 0.205 inches
to 0.875 inches, with a preferred range of thicknesses being in the
range from 0.205 inches to 0.595 inches.
[0082] The slab heating temperature must be controlled to
completely dissolve the Nb precipitates, and, depending on the Nb,
C and N levels in the steel, is chosen to ensure complete solution
of all alloy carbides and nitrides. The minimum reheating
temperature required to achieve this goal depends in large part on
the Nb content of the steel, as further discussed in the Examples
below. Preferably, a reheating temperature of approximately
2300.degree. F., which is well above the minimum required reheating
temperature for compositions made according to the invention (as
shown below), is utilized.
[0083] The rolling temperature must likewise be controlled to
ensure that rolling is completed in the fully austenitic phase
field. It is well-known that the austenite phase starts to
decompose to ferrite+pearlite and lower temperature transformation
products below the transformation start (Ar.sub.3) temperature,
which, for steel compositions according to the invention, is in the
range of from about 1250.degree. F. to about 1350.degree. F. Thus,
it is preferable to maintain the rolling temperature at well in
excess of the Ar.sub.3 temperature, to ensure that the skelp is
fully austenitic during rolling. Thus, a rolling temperature of
approximately 1500.degree. F., well above the Ar.sub.3 temperature,
is preferably utilized.
[0084] Following the rolling step, the skelp is then passed through
a runout table 7, where the skelp is cooled with water to a coiling
temperature in the range of about 850.degree. F. to about
950.degree. F.--well below the 1100.degree. F. to 1200.degree. F.
coiling temperature which is typically used in forming the skelp
for other as-welded casing products, as described above. The skelp
is then passed to a coiler 8, where it is formed into a hot-rolled
steel coil 9. The purpose of coiling at a lower temperature is to
produce a largely bainitic microstructure in the skelp, which will
strengthen during the subsequent pipe forming operation.
[0085] Particularly, it has been found that the use of a coiling
temperature of about 850.degree. F. to about 950.degree. F. is
critical to obtaining a skelp having the desired bainitic
microstructure, which is suitable for forming a casing product of
this invention having the desired minimum yield strength. The use
of the preferred composition, together with the steel processing
procedure described above, has been found to produce a skelp having
a yield strength of approximately 80 ksi (552 MPa). Upon formation
of the skelp so obtained into pipe, using the pipe-formation method
described hereinbelow, an increase in yield strength of
approximately 25 to 30 ksi (172 to 207 MPa) has been observed.
[0086] Once processing of the skelp has been completed, the coiled
skelp is then transferred to a pipe mill for pipe formation. The
preferred pipe formation process, facets of which are known in the
art, utilizes electric resistance welding (ERW) to produce a forged
weld along the pipe seam. The use of ERW in the manufacturing of
steel pipe is well known in the pipe manufacturing industry. While
the use of ERW is preferred in forming pipe from skelp made
according to the invention, other welding methods known in the art
of pipe formation could likewise be utilized in practicing the
invention. Such methods include TIG (tungsten inert gas) welding,
electron beam welding, and laser welding, to name but a few.
[0087] The preferred pipe formation process utilizes a coiled skelp
made according to the invention as described hereinabove, which has
a thickness that is approximately the ultimate pipe wall thickness
and a width that is a multiple of the ultimate pipe circumference.
For example, if the intent is to make 4.5'' (outside
diameter).times.0.250'' (wall thickness) pipe, the skelp would be
rolled to a nominal 0.250'' thick and 71.2'' wide (i.e. 5 multiples
of the desired pipe circumference), for slitting into 5 strips of
equal width.
[0088] The as-rolled coil is first slit into multiples of the
desired input width corresponding to the desired pipe size. The
dimensions may vary somewhat depending on the specific pipe mill
used. For example, at one mill, to make 4.5 ''.times.0.250'' pipe,
the nominal slit width may be 13.90''; while at another mill, to
make 5.5 ''.times.0.304'' pipe, the nominal slit width may be
16.90'' and for 7''.times.0.362'' pipe, the slit width may be
21.61''; while at still another mill, the slit widths for
4.5''.times.0.250 '', 5.5''.times.0.304'' and 7 ''.times.0.362''
may be 13.96 '', 17.08'' and 21.58'' respectively. The slit strips
are then fed into the pipe mill for forming, welding and sizing, to
produce a casing product having the desired final dimensions.
[0089] While in the preferred embodiment of the invention the
coiled skelp is slit into multiple strips for pipe formation, this
slitting procedure is not necessary to obtain the benefits of the
invention. For example, a hot-rolled skelp could be produced
according to the invention in which the width of the skelp is
approximately equal to the desired pipe circumference, thereby
eliminating the need for slitting of the skelp into strips prior to
pipe formation.
[0090] The stages in the pipe formation process are shown in FIGS.
2A-4A, with the cross-section of the skelp at each stage shown in
corresponding FIGS. 2B-4B. In a typical pipe mill, the strip or
skelp 10 is introduced into the rollers 20, as shown in FIG. 2A.
The action of rollers 20 on strip 10 causes strip 10 to be formed
into a tube, such that the opposite edges of the strip are brought
into juxtaposition with one another, as shown in FIG. 3A.
Additional rollers 20 serve to hold the edges of strip 10, now in
tubular form, against one another while the tube is passed through
a work coil 30, as shown in FIG. 4A. The work coil 30 generates a
magnetic field which serves to induce an electrical current in the
pipe, of sufficient strength that the pipe is heated through
electrical resistance to the point that the touching edges of strip
10 are welded together at 40.
[0091] Several steel compositions have successfully been prepared
according to the invention, and have been utilized to form
as-welded casing products having the desired minimum yield strength
in the range of 80 ksi (552 MPa) to 125 ksi (862 MPa).
EXAMPLE I
[0092] Two highly preferred steel compositions which have been
successfully prepared and formed into pipe, using the methods
described hereinabove, and shown to yield as-welded casing products
having the highly preferred minimum yield strength in excess of 100
ksi (689 MPa), are listed in Table 1.
TABLE-US-00001 TABLE 1 Composition % C % Mn % Si % Al % Cr % Mo %
Nb % Ti % V A 0.040-0.055 1.82-1.90 0.26-0.34 0.022-0.035 0.15-0.20
0.29-0.32 0.075-0.085 0.015-0.025 0.006 B 0.045-0.060 1.65-1.75
0.12-0.18 0.015-0.025 0.15-0.20 0.28-0.32 0.040-0.050 0.008-0.015
0.05-0.06
[0093] A total of twelve heats (batches) corresponding to
Composition A were used to prepare skelps as described hereinabove,
namely, by (i) heating the cast steel slab to a temperature of
approximately 2300.degree. F.; (ii) hot-rolling the heated slab in
a steckel mill at a temperature of approximately 1500.degree. F.,
to obtain a skelp having a thickness of approximately 0.25 inches;
(iii) cooling the skelp with water to a coiling temperature in the
range of 850.degree. F. to 950.degree. F.; and (iv) forming the
skelp into a coil using conventional coiling methods. It was found
that the minimum slab heating temperature for Composition A must be
above about 2170.degree. F. in order to completely dissolve the Nb
precipitates.
[0094] The precise composition of each of the twelve heats prepared
according to Composition A is listed in Table 2.
TABLE-US-00002 TABLE 2 % Heat % C Mn % Si % Al % Cr % Mo % Nb % Ti
% V A1 0.050 1.83 0.293 0.034 0.16 0.295 0.077 0.017 0.006 A2 0.046
1.80 0.312 0.041 0.17 0.296 0.077 0.020 0.006 A3 0.046 1.85 0.285
0.030 0.17 0.294 0.079 0.018 0.006 A4 0.051 1.82 0.286 0.038 0.16
0.289 0.076 0.017 0.006 A5 0.048 1.82 0.298 0.040 0.18 0.303 0.079
0.020 0.006 A6 0.049 1.83 0.282 0.039 0.16 0.295 0.076 0.020 0.006
A7 0.058 1.83 0.302 0.037 0.17 0.296 0.077 0.016 0.006 A8 0.056
1.83 0.327 0.026 0.16 0.299 0.078 0.015 0.009 A9 0.048 1.83 0.328
0.030 0.16 0.293 0.077 0.020 0.010 A10 0.055 1.84 0.328 0.026 0.16
0.298 0.079 0.018 0.010 A11 0.048 1.87 0.324 0.026 0.18 0.294 0.079
0.021 0.010 A12 0.049 1.86 0.304 0.029 0.16 0.296 0.079 0.018
0.009
[0095] The skelps obtained from each of Heats A1-A12 were tested
for yield strength and ultimate tensile strength, with the yield
strength of the skelps ranging from 75.4 ksi (520 MPa) to 91.4 ksi
(640 MPa), and the ultimate tensile strength of the skelps ranging
from 100.9 ksi (696 MPa) to 111.9 ksi (772 MPa). Those skelps were
then formed into pipes having an outer diameter of 4.5 inches and a
wall thickness of 0.25 inches, using the pipe formation method
described hereinabove, and tested to determine the minimum yield
strength and ultimate tensile strength for each pipe. The results
of that strength testing are listed in Table 3.
TABLE-US-00003 TABLE 3 Ultimate Tensile Heat Pipe No. Yield
Strength (ksi) Strength (ksi) A1 1 102.7 116.8 2 111.9 114.6 3
100.8 115.9 4 101.2 111.6 A2 1 103.2 118.0 2 106.7 118.5 3 104.3
120.9 A3 1 103.6 112.5 2 105.3 116.1 3 104.1 112.4 4 108.2 120.7 A4
1 108.0 121.8 2 103.5 113.4 3 106.5 124.6 4 97.3 122.7 5 104.8
119.4 6 107.8 119.9 7 110.8 122.7 A5 1 109.1 119.9 2 104.6 120.6 3
103.9 117.0 4 100.7 120.3 5 103.4 119.9 A6 1 112.8 118.9 2 107.4
116.5 3 107.9 121.0 4 109.7 121.4 5 109.3 120.5 6 108.2 118.3 7
105.9 117.1 8 108.2 119.9 9 106.2 115.1 10 111.6 117.2 A7 1 113.2
121.5 2 111.2 118.9 3 107.0 113.8 4 109.8 123.8 5 108.0 123.8 6
106.8 117.7 7 109.1 122.5 8 109.3 124.5 9 105.7 118.5 10 107.0
123.5 11 105.1 117.7 12 106.3 121.2 A8 1 106.2 114.8 2 114.2 122.6
3 113.6 121.0 4 111.0 121.0 A9 1 111.1 118.2 A10 1 105.3 121.9 2
113.5 125.0 3 111.1 122.1 4 115.3 122.2 A11 1 111.4 117.1 2 107.7
119.0 3 102.0 116.7 4 114.3 123.0 A12 1 113.2 122.5
[0096] Additionally, skelps from each of heats A10 and A12 were
formed into pipes having an outer diameter of 5.5 inches and a wall
thickness of 0.29 inches, using the pipe formation method described
hereinabove, and tested to determine the minimum yield strength and
ultimate tensile strength for each pipe. The results of that
strength testing are listed in Table 4.
TABLE-US-00004 TABLE 4 Ultimate Tensile Heat Pipe No. Yield
Strength (ksi) Strength (ksi) A10 1 110.4 117.9 2 105.3 114.0 A12 1
112.2 118.0 2 107.5 118.0 3 111.0 116.1 4 107.4 115.0 5 111.5 119.1
6 111.4 115.0
[0097] As can be seen from Tables 3 and 4, of the 67 representative
pipes made according to the preferred composition (Composition A)
and preferred processing method of the invention, 66 of those pipes
obtained the highly preferred minimum yield strength of at least
100 ksi (689 MPa). Similarly, each of the 67 pipes made according
to the composition and method of the invention obtained the highly
preferred minimum ultimate tensile strength of at least 110 ksi
(758 MPa). Thus, it is clear from the above data that the methods
of the invention were successful in obtaining as-welded pipe for
use in casing products for the OCTG market, having a minimum yield
strength of about 100 ksi and a minimum ultimate tensile strength
of about 110 ksi.
EXAMPLE II
[0098] A total of 2 heats corresponding to Composition B were
likewise used to prepare skelps as described hereinabove, namely,
by (i) heating the cast steel slab to a temperature of
approximately 2300.degree. F.; (ii) hot-rolling the heated slab in
a steckel mill at a temperature of approximately 1500.degree. F.,
to obtain a skelp having a thickness of approximately 0.25 inches;
(iii) cooling the skelp with water to a coiling temperature in the
range of 850.degree. F. to 950.degree. F.; and (iv) forming the
skelp into a coil using conventional coiling methods. In contrast
to the slabs prepared according to Composition A, a lower minimum
slab heating temperature of above about 2060.degree. F. was
required for Composition B, as a result of the lower Nb content of
Composition B.
[0099] The precise composition of each of the 2 heats prepared
according to Composition B is listed in Table 5.
TABLE-US-00005 TABLE 5 % Heat % C Mn % Si % Al % Cr % Mo % Nb % Ti
% V B1 0.052 1.67 0.155 0.026 0.18 0.285 0.043 0.01 0.053 B2 0.048
1.68 0.141 0.019 0.18 0.286 0.042 0.011 0.052
[0100] The skelps obtained from Heats B1 and B2 were tested for
yield strength and ultimate tensile strength, and were found to
have yield strengths of 74.2 ksi (512 MPa) (B1) and 78.0 ksi (538
MPa) (B2), and ultimate tensile strengths of 102.5 ksi (707 MPa)
(B1) and 104.7 ksi (722 MPa) (B2). Those skelps were then formed
into pipes having an outer diameter of 4.5 inches and a wall
thickness of 0.25 inches, using the pipe formation method described
hereinabove, and tested to determine the minimum yield strength and
ultimate tensile strength for each pipe. The results of that
strength testing are listed in Table 6.
TABLE-US-00006 TABLE 6 Ultimate Tensile Heat Pipe No. Yield
Strength (ksi) Strength (ksi) B1 1 101.8 112.7 2 101.0 112.2 3
104.2 115.5 4 102.9 113.1 5 103.4 114.5 B2 1 103.5 112.6 2 100.8
111.3 3 105.2 112.6 4 102.2 112.5 5 102.0 111.7
[0101] As can be seen from Table 6, each of the ten representative
pipes made according to the preferred composition (Composition B)
and preferred processing method of the invention obtained the
highly preferred minimum yield strength of at least 100 ksi (689
MPa) and the highly preferred minimum ultimate tensile strength of
at least 110 ksi (758 MPa). Thus, it is clear from the above data
that the methods of the invention were again successful in
obtaining as-welded pipe for use in casing products for the OCTG
market, having a minimum yield strength of about 100 ksi and a
minimum ultimate tensile strength of about 110 ksi.
EXAMPLE III
[0102] In addition to the foregoing examples of as-welded pipes
made according to the composition and method of the invention, a
number of additional as-welded pipes were made using the identical
steel processing and pipe formation methods described above, but
using different preferred steel compositions--which differed from
those of Compositions A and B primarily in the fact that they
contained higher amounts of carbon and lower amounts of Nb and V
than Compositions A and B of Examples I and II. Three such
compositions are listed in Table 7.
TABLE-US-00007 TABLE 7 Compo- % % sition % C Mn % Si % Al % Cr Mo %
Nb % Ti % V C 0.058 1.86 0.125 0.017 0.06 0.244 0.043 0.008 0.001 D
0.066 1.87 0.128 0.02 0.04 0.246 0.036 0.008 0.001 E 0.064 1.75
0.288 0.019 0.06 0.246 0.047 0.008 0.003
[0103] Skelps were prepared from one heat corresponding to each of
Compositions C, D and E as described hereinabove, namely, by (i)
heating the cast steel slab to a temperature of approximately
2300.degree. F.; (ii) hot-rolling the heated slab in a steckel mill
at a temperature of approximately 1500.degree. F., to obtain a
skelp having a thickness of 0.25 inches; (iii) cooling the skelp
with water to a coiling temperature in the range of 850.degree. F.
to 950.degree. F., and (iv) forming the skelp into a coil using
conventional coiling methods.
[0104] The skelps obtained from heats C and E were tested for yield
strength and ultimate tensile strength, with the yield strength of
the skelps ranging from 77.4 ksi (534 MPa) to 86.5 ksi (596 MPa),
and the ultimate tensile strength of the skelps ranging from 92.8
ksi (640 MPa) to 106.6 ksi (735 MPa).
[0105] The skelps of Heats C, D and E were then formed into pipes
having an outer diameter of 4.5 inches and a wall thickness of 0.25
inches, using the pipe formation method described hereinabove, and
tested to determine the minimum yield strength and ultimate tensile
strength for each pipe. The results of that strength testing are
listed in Table 8.
TABLE-US-00008 TABLE 8 Ultimate Tensile Heat Pipe No. Yield
Strength (ksi) Strength (ksi) C 1 100.6 110.1 2 97.9 113.8 3 102.5
114.9 4 100.0 107.4 5 97.9 109.8 6 99.9 110.9 D 1 98.2 107.5 2 97.4
108.7 E 1 100.5 111.0 2 102.0 110.8 3 104.9 116.6 4 100.6 115.7
[0106] Thus, while the as-welded pipes made according to
Compositions C, D and E did not always achieve the highly desired
minimum yield strength of 100 ksi (689 MPa) or the highly desired
minimum ultimate tensile strength of at least 110 ksi (758 MPa),
each of those pipes did achieve the desired minimum yield strength
well in excess of 80 ksi (552 MPa). It is believed that the
slightly lower yield strength and tensile strength of pipes made
from Compositions C, D and E, relative to those made from
Compositions A and B, is attributable to the lower levels of Nb
which are present in Compositions C, D and E.
EXAMPLE IV
[0107] Four additional heats corresponding to Composition A were
used to prepare skelps as described hereinabove, namely, by (i)
heating the cast steel slab to a temperature of approximately
2300.degree. F.; (ii) hot-rolling the heated slab in a steckel mill
at a temperature of approximately 1500.degree. F., to obtain a
skelp having a thickness of 0.25 inches; (iii) cooling the skelp
with water to a coiling temperature in the range of 850.degree. F.
to 950.degree. F., and (iv) forming the skelp into a coil using
conventional coiling methods. The precise composition of each of
those heats is listed in Table 9.
TABLE-US-00009 TABLE 9 % Heat % C Mn % Si % Al % Cr % Mo % Nb % Ti
% V A13 0.042 1.82 0.295 0.035 0.16 0.303 0.077 0.020 0.005 A14
0.044 1.81 0.285 0.042 0.16 0.287 0.080 0.020 0.005 A15 0.048 1.85
0.284 0.037 0.17 0.294 0.079 0.018 0.005 A16 0.050 1.82 0.291 0.033
0.17 0.292 0.076 0.015 0.005
[0108] The skelps obtained from each of Heats A13-A16 were formed
into pipes having an outer diameter of 5.5 inches and a wall
thickness of 0.304 inches, using the pipe formation method
described hereinabove, and tested to determine the minimum yield
strength and ultimate tensile strength for each pipe. The results
of that strength testing are listed in Table 10.
TABLE-US-00010 TABLE 10 Ultimate Tensile Heat Pipe No. Yield
Strength (ksi) Strength (ksi) A13 1 104.8 114.9 2 98.9 108.9 3
106.1 110.2 4 106.3 113.3 5 101.9 109.5 6 100.6 107.7 7 109.8 121.3
8 101.4 107.6 9 103.3 113.9 10 104.0 108.6 A14 1 102.5 112.7 2
102.3 110.6 3 100.0 110.4 4 102.1 107.6 5 100.4 109.4 6 107.9 116.5
7 103.4 112.5 8 103.8 114.3 A15 1 105.2 115.6 2 105.2 109.7 3 107.4
112.6 4 104.5 115.0 5 103.3 110.4 6 103.9 112.2 7 103.9 108.5 8
105.9 109.9 9 105.2 113.2 10 105.2 110.8 A16 1 103.8 113.2 2 102.7
107.5 3 97.4 113.7 4 104.7 114.9 5 108.0 116.4 6 103.7 112.9 7 99.9
107.1 8 108.7 120.0 9 106.2 115.4 10 107.7 114.5 11 102.1 113.1
[0109] As can be seen from Table 10, while each of the 39
representative pipes made from Heats A13-A16 and the preferred
processing method of the invention obtained a minimum yield
strength well in excess of the 80 ksi (552 MPa) preferred minimum
yield strength, a number of those pipes did not achieve the highly
preferred minimum yield strength of at least 100 ksi (689 MPa) or
the highly preferred minimum ultimate tensile strength of at least
110 ksi (758 MPa).
[0110] In order to consistently obtain pipe having the highly
preferred minimum yield strength of at least 100 ksi (689 MPa) for
this size pipe at this particular pipe mill, it was theorized that
a higher carbon content would increase the yield strength and
ultimate tensile strength of the pipe, while still retaining the
benefits of the invention. Thus, two additional heats generally
corresponding to Composition A in other parameters, but having a
higher carbon content of at least about 0.075%, were prepared. This
compositions for those two heats are listed in Table 11.
TABLE-US-00011 TABLE 11 % Heat % C Mn % Si % Al % Cr % Mo % Nb % Ti
% V F1 0.075 1.84 0.295 0.025 0.19 0.296 0.076 0.019 0.007 F2 0.078
1.85 0.309 0.019 0.16 0.291 0.078 0.015 0.007
[0111] The skelps obtained from each of Heats F1 and F2 were
likewise formed into pipes having an outer diameter of 5.5 inches
and a wall thickness of 0.304 inches, using the pipe formation
method described hereinabove, and tested to determine the minimum
yield strength and ultimate tensile strength for each pipe. The
results of that strength testing are listed in Table 12.
TABLE-US-00012 TABLE 12 Ultimate Tensile Heat Pipe No. Yield
Strength (ksi) Strength (ksi) F1 1 106.0 116.1 2 109.4 121.9 3
107.4 114.5 4 109.3 116.9 5 111.9 116.6 6 113.0 119.7 7 112.9 119.4
8 107.7 116.5 9 112.3 122.2 F2 1 107.6 117.4 2 104.4 113.0 3 106.5
119.8 4 108.2 117.7 5 107.7 120.4 6 111.8 119.8 7 110.4 119.5 8
109.5 118.6
[0112] As can be seen from Table 12, each of the 17 representative
pipes made according to the preferred composition (Composition F)
and preferred processing method of the invention obtained the
highly preferred minimum yield strength of at least 100 ksi (689
MPa) and the highly preferred minimum ultimate tensile strength of
at least 110 ksi (758 MPa). Thus, it is clear from the above data
that the methods of the invention were again successful in
obtaining as-welded pipe for use in casing products for the OCTG
market, having a minimum yield strength of about 100 ksi and a
minimum ultimate tensile strength of about 110 ksi.
[0113] The foregoing description and drawings merely explain and
illustrate the invention, and the invention is not so limited as
those skilled in the art who have the disclosure before them will
be able to make modifications and variations therein without
departing from the scope of the invention.
* * * * *