JPH05212539A - Production of steel tube for contact weld - Google Patents

Abstract

PURPOSE:To embody excellent workability in site welding and increase toughness in joining part by welding a Ni-base high alloy or the like at both tube ends of a low alloy or carbon steel tube by build-up welding, butting both tube ends and executing site welding. CONSTITUTION:A stainless steel, 9% nickel steel and Ni-base high alloy with the same diameter and thickness as the tube 2 are build-up welded 1 at >=20mm in length to the steel tube 2 of the low alloy or the carbon steel, a test piece 3 is cut and contact weld is executed after that. A Charpy test piece 6 contg. HAZ 4 is picked from the welding zone 5. Then, the toughness strength of this nickel high alloy base is >=5kgf.m as welded and high toughness in the contact welding zone can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel pipe for contact welding which has excellent on-site weldability and excellent low temperature toughness at the joint. This method is used for on-site welding of large diameter line pipes for transportation of natural gas and crude oil.

[0002]

2. Description of the Related Art The contact welding method is being adopted for relay welding of large-diameter line pipes on site because it is possible to obtain a highly efficient and stable weld. However, there is a problem that it is difficult to secure the low temperature toughness in the welded joint and the heat affected zone (HAZ) where the contact welding is performed. That is, in this welding method, the end portion of the steel pipe is heated until it is in a molten state and then pressure-bonding is performed, so that the structure of the joint portion becomes coarse and the low temperature toughness is significantly deteriorated. In addition, welding defects at the joint also pose a problem.

In Japanese Patent Laid-Open No. 1-92320, heat treatment after contact welding (PWHT: post weld heat t) is disclosed.
The joint toughness is improved by reatment), but 0
It is an evaluation of the toughness value at 0 ° C, and it cannot be said that sufficient low temperature toughness is obtained. In addition, in PWHT in cold regions where low temperature toughness is required, 800 ° C to 5
The cooling rate up to 00 ° C is regulated to 5 to 15 ° C / s, which is difficult in operation (freezing of cooling water, etc.), and treatment by air cooling is desired.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to propose an effective method for obtaining high toughness as-welded (hereinafter, as-welded) at a joint portion including a HAZ of a contact weld portion. That is, in the low alloy, which is usually used as a steel pipe for line pipes, or the steel pipe of carbon steel,
Stainless steel, which is less susceptible to deterioration of low temperature toughness due to heat effect,
By welding 9% Ni steel or Ni-base alloy,
It is intended to improve the microstructure in the vicinity of the contact weld portion and obtain excellent low temperature toughness of the joint portion.

Further, an object of the present invention is to eliminate the PWHT for improving the toughness after contact welding by improving the toughness in advance at the time of manufacturing a steel pipe. That is, the workability is excellent in the field welding, and the toughness of the contact weld portion is to be obtained. Particularly effective in the field welding of cold shore and offshore line pipes.

[0006]

SUMMARY OF THE INVENTION The present invention is a low alloy or carbon steel tube with stainless steel, 9% N
This is a method for manufacturing a steel pipe for contact welding, which is characterized in that i steel or Ni-based high alloy is welded for 20 mm or more and both pipe ends are butt-welded together.

[0007]

In the present invention, the following facts have been found out as a result of a detailed investigation regarding the relationship between the toughness of the contact welded joint due to the difference in steel type. In ordinary low alloy or carbon steel, ferrite side plates are formed as they are welded, and it is impossible to improve the toughness of the contact weld joint. On the other hand, in the case of stainless steel or Ni-base high alloy steel, the low temperature toughness of the contact weld joint is not deteriorated due to the heat effect, and a good toughness value is obtained.

That is, the addition of Ni (9% by weight or more) is the best method for improving the toughness in a structure where the welded part is exposed to high temperature and the structure is significantly coarsened and the oxygen content of the deposited metal is high. . However, if a large diameter steel pipe such as a line pipe is manufactured with high Ni, no economic merit can be obtained. Therefore, only the contact weld abutment part has high Ni.
It has been found that a high Ni steel weld surplus is provided in the longitudinal direction of the pipe end of a low alloy or plain steel pipe to make it steel.
The composition of the deposited metal is preferably austenitic stainless steel and Ni-base high alloy. Also,
Submerged arc welding or manual welding is desirable for the extra portion of the pipe end.

The method of improving toughness according to the present invention is mainly useful for relay welding of large-diameter line pipes, but it can also be used for welding steel plates, shaped steels and the like. For field welding, welding other than contact welding (for example, shielded act
It is also effective for improving the toughness of ive gas welding) and omitting the PWHT process.

With respect to the length of the buildup, since the length must be such that contact weld welding is sufficiently performed, the lower limit is set to 20 mm (total deviation +10 mm). Further, if it is too long, the economic merit is lost, so it is desirable to set it to 100 mm or less.

[0011]

EXAMPLES Next, the present invention will be explained by examples. A low-alloy or carbon-steel pipe 2 having a size as shown in Table 1 was welded 1 with a stainless steel, 9% Ni steel and a Ni-base high-alloy having the same diameter and the same thickness, and then a test piece as shown in FIG. Three
Was cut out and contact welding was performed. A Charpy test piece 6 containing HAZ 4 was taken from the welded portion 5 as shown in FIG.

Steel H was remarkably poor in as-welded toughness obtained by contact welding the ordinary low alloy steel as it was.
Further, although an improvement in toughness was observed after PWHT of Japanese Patent Laid-Open No. 1-92320 was performed on H steel, it was insufficient at 5 kgf · m or less. Steel J had a small amount of Ni and was insufficient in toughness. On the other hand, the steels A to G had an as-welded value of 5 kgf · m or more and good contact weld toughness was obtained.

[0013]

[Table 1]

[0014]

According to the present invention, it becomes possible to effectively improve the toughness of the joint portion including the HAZ of the steel pipe subjected to contact weld welding, and it becomes possible to omit the PWHT process which impairs workability in cold regions. It became possible to install a line pipe with excellent safety.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a contact weld test piece.

FIG. 2 is a schematic explanatory view of a Charpy test piece.

[Explanation of symbols]

 1 Overlay welding 2 Steel pipe of low alloy or carbon steel 3 Contact weld test piece 4 HAZ 5 Welded portion 6 Charpy test piece

Claims (1)

[Claims] 1. A low alloy or carbon steel pipe is welded with stainless steel, 9% Ni steel or Ni-base high alloy for 20 mm or more by overlay welding on both pipe ends, and both pipe ends are butt-field welded. Method for manufacturing contact weld steel pipe.