Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1997-01-15
1998-12-15
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148593, 148609, 148602, 219 61, 219 602, C21D 810, C21D 802
Patent
active
058491163
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a production method for a steel material and a steel pipe having excellent corrosion resistance and weldability. More particularly, this invention relates to a method for producing, easily and at a low cost, a steel material and a steel pipe having excellent corrosion resistance in an environment containing wet carbon dioxide and a small amount of wet hydrogen sulfide, and having also excellent weldability, for oil well pipes for the exploitation and production of petroleum
atural gases, line pipes used for the transportation, or vessels used for storage and various processings.
BACKGROUND ART
Petroleum and natural gases produced in recent years have become more and more of the type which contains wet carbon dioxide and hydrogen sulfide. It is well known that under such an environment, carbon steels and low alloy steels corrode remarkably. To transport such corrosive petroleum and natural gases, it has been customary in the past to add corrosion inhibitor as an anticorrosion countermeasure. In the case of offshore oil wells, however, it is enormously expensive to add and recover the corrosion inhibitor, and due to the problem of ocean pollution, the use of the corrosion inhibitor has become more and more difficult. For these reasons, a need for corrosion-resistant materials which do not need the addition of a corrosion inhibitor has become greater in recent years.
The introduction of stainless steels was first examined as corrosion-resistant materials for petroleum and natural gases containing large quantities of carbon dioxide. As described, for example, in L. J. Klein, "Corrosion", '84, Paper No. 211, a martensitic stainless steel containing about 0.2% of C and about 12 to 13% of Cr, as typified by AISI420 steel, has been widely used as steels which have high strength and are relatively economical. In order to acquire the high strength necessary for the oil well pipe by this steel, however, this steel involves the drawbacks that the steel cannot be tempered at a relatively high temperature and thus its impact toughness is low. Since the AISI420 steel contains about 0.2% of C, its weldability is very poor. In other words, it involves the problems that the hardness of a welding heat affected zone is very high, the pre-heating temperature and the post-heating temperature for preventing weld crack are very high, and the toughness of the welding heat affected zone is very poor.
API (American Petroleum Institute) standardizes AISI410 steel having a relatively lower C content as the line pipe, and "NKK Engineering Report", 1989, No. 129, pp. 15 to 22, reports an example where the AISI410 steel is produced as a UOE steel pipe. As this report describes, however, the AISI410 steel still has the problems that it cannot be converted to the austenite monophase at a high temperature, and because coarse delta-ferrite is formed during welding, the impact toughness of the weld portion is extremely low.
As described exemplarily in Japanese Unexamined Patent Publication (Kokai) Nos. 63-134630 and 63-238217, the martensitic stainless steel pipes typified by the AISI420 steel have been produced in the past as seamless steel pipes by a seamless steel pipe rolling method. However, the seamless steel pipes have the drawbacks that the production yield and productivity are extremely low, and the production cost is very high. One of the reasons why the cost of the seamless steel pipes is very high is because the steel pipes must be subjected to quenching-tempering heat-treatment after pipe making. Further, in the case of low C martensitic stainless steels which reduce as much as possible the C or C and N contents so as to improve the corrosion resistance or weldability, these steels cannot be produced easily by the seamless steel pipe rolling method.
Japanese Unexamined Patent Publication (Kokai) No. 4-191319 and No. 4-191320 disclose a method of producing a low carbon matertensitic stainless steel as a steel pipe, and Japanese Unexamined Patent Publication (Kokai) No. 4-99127 and No.
REFERENCES:
J. of Corrosion, paper No. 211, 1984, by J. Klein NKK Engineering Report, 1989, No. 129, pp. 15-22.
Miyasaka Akihiro
Motoyoshi Takashi
Obata Masaaki
Nippon Steel Corporation
Yee Deborah
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