U.S. patent application number 09/341722 was filed with the patent office on 2002-01-31 for method for making seamless tubing with a stable elastic limit at high application temperatures.
Invention is credited to HEINZ, GERD, KOSCHLIG, BERNHARD, NIEDERHOFF, KURT, RING, MARKUS, VON HAGEN, INGO.
Application Number | 20020011284 09/341722 |
Document ID | / |
Family ID | 7818451 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020011284 |
Kind Code |
A1 |
VON HAGEN, INGO ; et
al. |
January 31, 2002 |
METHOD FOR MAKING SEAMLESS TUBING WITH A STABLE ELASTIC LIMIT AT
HIGH APPLICATION TEMPERATURES
Abstract
The invention relates to a process for producing seamless line
pipes within the quality grade range X 52 to X 90, with a stable
yield strength up to a temperature of use of 200.degree. C., and
with an essentially constant stress-strain characteristic, by
hot-rolling a pipe blank made from a steel which contains the
following alloying elements (% by weight): 1 C 0.06-0.18% Si max.
0.40% Mn 0.80-1.40% P max. 0.025% S max. 0.010% Al 0.010-0.060% Mo
max. 0.50% V max. 0.10% Nb max. 0.10% N max. 0.015% W
>0.30-1.00% remainder iron and usual impurities, in which
process the hot rolling is followed by reheating of the cooled
pipes to above AC.sub.3, after which the pipes are quenched to
below 100.degree. C. at a cooling rate of at least 15.degree. C./s
and are then tempered within the temperature range from 500 to
700.degree. C.
Inventors: |
VON HAGEN, INGO; (KREFELD,
DE) ; RING, MARKUS; (DUISBURG, DE) ; HEINZ,
GERD; (MEERBUSCH, DE) ; KOSCHLIG, BERNHARD;
(RATINGEN, DE) ; NIEDERHOFF, KURT; (RATINGEN,
DE) |
Correspondence
Address: |
THOMAS C PONTANI
COHEN PONTANI LIEBERMAN & PAVANE
551 FIFTH AVENUE
SUITE 1210
NEW YORK
NY
10176
|
Family ID: |
7818451 |
Appl. No.: |
09/341722 |
Filed: |
July 15, 1999 |
PCT Filed: |
December 12, 1997 |
PCT NO: |
PCT/DE97/02943 |
Current U.S.
Class: |
148/320 ;
148/593; 420/127 |
Current CPC
Class: |
C21D 9/08 20130101; C21D
8/10 20130101; C22C 38/12 20130101 |
Class at
Publication: |
148/320 ;
148/593; 420/127 |
International
Class: |
C22C 038/12; C22C
038/00; C21D 009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 15, 1997 |
DE |
197 02 823.3 |
Claims
1. A process for producing seamless line pipes within the quality
grade range X 52 to X 90, with a stable yield strength up to a
temperature of use of 200.degree. C., and with an essentially
constant stress-strain characteristic, by hot-rolling a pipe blank
made from a steel which contains the following alloying elements (%
by weight):
4 C 0.06-0.18% Si max. 0.40% Mn 0.80-1.40% P max. 0.025% S max.
0.010% Al 0.010-0.060% Mo max. 0.50% V max. 0.10% Nb max. 0.10% N
max. 0.015% W >0.30-1.00%
remainder iron and usual impurities, in which process the hot
rolling is followed by reheating of the cooled pipes to above
AC.sub.3, after which the pipes are quenched to below 100.degree.
C. at a cooling rate of at least 15.degree. C./s and are then
tempered within the temperature range from 500 to 700.degree.
C.
2. The process as claimed in claim 1, wherein up to 0.050% Ti is
added to the steel which is to be used, for fixation of
nitrogen.
3. The process as claimed in one of claims 1 to 2, wherein the
steel which is to be used contains from 0.35 to 0.70%, in
particular from 0.35 to 0.40%, W.
4. The process as claimed in one of claims 1 to 3, wherein the
steel which is to be used contains from 0.05 to 0.40%, in
particular from 0.10 to 0.25%, Mo.
5. The process as claimed in one of claims 1 to 4, wherein the
steel which is to be used contains at least 0.04% V.
Description
DESCRIPTION
[0001] The invention relates to a process for producing seamless
line pipes within the quality grade range X 52 to X 90.
[0002] In the course of the exploration of deposits of
hydrocarbons, deposits are increasingly being discovered which are
difficult to convey owing to the fact that the hydrocarbons (e.g.
natural gas) are at relatively high temperatures of, for example,
from 100 to 200.degree. C. The materials which can be used for line
pipes under such conditions not only have to be sufficiently
weldable and to have a certain resistance to corrosion, but also
have to have a comparatively stable yield strength. For example,
the reduction in yield strength at a temperature of 160.degree. C.
compared to the yield strength at room temperature should be as low
as possible. Furthermore, an essentially constant stress-strain
characteristic is required, i.e. the so-called Luders strain should
be as low as possible.
[0003] It is generally relatively rare to use tungsten as an
alloying element. As a strong carbide-forming element, it is
regularly used to produce cold-work, hot-work and high-speed
steels. It increases their high-temperature strength, ability to
withstand tempering and, in particular, the wear resistance at high
temperatures. Tungsten acts in a similar way to molybdenum, so that
it can replace molybdenum in a ratio of 2:1.
[0004] In modern power plant construction, ferritic alloys
containing 9 to 12% chromium which are able to withstand high
temperatures are used for steam pipelines. For these steels, it is
known to add from 1 to 2% tungsten to the alloy in order to
increase the creep rupture strength. Examples of such steels are
the alloys P 92 and P 122 from Japan and the European-developed
material E 911.
[0005] Hitherto, there has been no knowledge whatsoever of using
tungsten as an alkalyne element for line pipe steels.
[0006] The object of the invention is to propose a method for the
production of seamless line pipes, in which method it is possible
to reliably set a quality grade in the range from X 52 to X 90 by
means of a quenching and tempering treatment and to ensure a stable
yield strength combined with an essentially constant stress-strain
characteristic up to temperatures of use of 200.degree. C.
[0007] According to the invention, this object is achieved by
hot-rolling of a pipe blank made from a steel of the following
composition (% by weight):
2 C 0.06-0.18% Si max. 0.40% Mn 0.80-1.40% P max. 0.025% S max.
0.010% Al 0.010-0.060% Mo max. 0.50% V max. 0.10% Nb max. 0.10% N
max. 0.015% W >0.30-1.00%
[0008] remainder iron and usual impurities.
[0009] Following the hot rolling and cooling of the pipes, they are
reheated to a temperature above AC.sub.3 and quenched to below
100.degree. C. at a cooling rate of at least 15.degree. C./s. Then,
the pipes are tempered within the temperature range from 500 to
700.degree. C., depending on the quality grade desired.
[0010] In many cases, for fixation of the nitrogen content, it is
recommended to add up to 0.050% Ti to the steel alloy used. The
tungsten content expediently lies in the range from 0.35 to 0.70%,
particularly preferably in the range from 0.35 to 0.40%. It is
recommended to set the vanadium content at at least 0.04%. A
molybdenum content in the range from 0.05 to 0.40%, preferably in
the range from 0.10 to 0.25%, has proven advantageous particularly
for the higher quality grades.
[0011] The steel alloy which is to be used for the hot rolling
according to the invention may perfectly well contain further
accompanying substances, such as those which are used in particular
for electric-furnace steelmaking, without its properties being
impaired. Examples of such accompanying substances are copper,
chromium and nickel. Expediently, the steel should contain at most
0.15% of each of these accompanying substances.
[0012] A line pipe which has been hot-rolled and quenched after
reheating according to the invention can be set at any desired
quality grade within the range from X 52 to X 90 by means of
quenching and tempering. The lower the tempering temperature
selected, the higher the strength characteristics which can be
achieved. The toughness properties are improved by increasing the
tempering temperatures. A line pipe which is produced according to
the invention has a stable yield strength at least up to a
temperature of use of 200.degree. C., i.e. the reduction in yield
strength is very low (<10%). The stress-strain characteristic is
essentially constant. The weldability, which is important for line
pipes, is guaranteed. The carbon equivalent according to IIW can be
set at relatively low levels. The molybdenum content can be limited
to very low values or may even be zero. Since tungsten is less
expensive than molybdenum, the alloy which is to be used according
to the invention costs less to produce.
[0013] The important addition of tungsten to the alloy, which is
the decisive factor for the invention, has produced a positive
effect which is surprising to the person skilled in the art. This
is to be illustrated below using an exemplary embodiment and a
comparative example. The stress-strain characteristic of specimens
of the two examples is illustrated in graphs in FIG. 1 (invention)
and FIG. 2 (comparison).
[0014] Tests were carried out on test specimens with a thickness of
35 mm in each case, which had been rolled in a pilger-rolling mill
train. The alloys used for the two examples are given in the
following table:
3 Element Invention Comparison C 0.13% 0.13% Mn 1.30% 1.25% Mo
0.15% 0.30% V 0.05% 0.05% Cr 0.10% 0.10% W 0.35% -- Ti 0.018%
0.018% N 70 ppm 70 ppm
[0015] For the steel used according to the invention, the carbon
equivalent was determined to have the value TE.sub.IIW=0.42 or
CE.sub.PCM=0.23. The carbon equivalent values for the comparison
steel were 0.44 and 0.24, respectively. The alloy of the steel used
according to the invention differs from the comparison alloy
essentially only in that the molybdenum content is 0.15% lower, and
an additional content of 0.35% tungsten is added instead. During
the testing of the strength properties at a test temperature of
160.degree. C., the yield strength of the steel used according to
the invention fell by only approx. 5%. As can be seen from the
stress-strain characteristic in FIG. 1, surprisingly the
stress-strain curves at room temperature (RT) and at the test
temperature of 160.degree. C. coincide virtually completely beyond
a plastic extension of approx. 0.7%. By comparison, the similar
stress-strain diagram for the molybdenum-alloyed comparison steel
which is illustrated in FIG. 2 reveals a very different behavior.
In this case, the stress-strain curve at the test temperature of
160.degree. C. lies significantly below the stress-strain curve at
room temperature over the entire range tested. This stress-strain
performance of the line pipe steel used according to the invention,
which is comparatively much more advantageous, was completely
unexpected.
[0016] At a tempering temperature of 670.degree. C., the tested
specimen of the steel according to the invention had a yield
strength of R.sub.p0.2=594 MPa, thus achieving the level of quality
grade X 85. The use of higher tempering temperatures makes it
possible to reduce the strength level, while lower temperatures
increase the strength level. Within the limits of the alloying
ranges according to the invention, it is possible to select alloys
which, by means of appropriate quenching and tempering treatment,
can produce the quality grade range from X 52 to X 90. In terms of
the notched-impact strength at a test temperature of -30.degree. C.
(specimen position: center of sheet, transverse), the tested steel
specimen according to the invention achieved a notched-impact
energy value of 92 J/cm.sup.2, which is regarded as extremely good
for the quality grade X 85. The weldability of the steel according
to the invention can be classified as entirely satisfactory, and
there is no evidence of the addition of tungsten to the alloy
having any adverse effect.
* * * * *