1. The basic requirements for the appearance of the welded seam of the straight seam steel pipe

Before the non-destructive testing of straight seam steel pipes, the weld appearance inspection shall meet the requirements. The welded joints used for pipe joints generally require the appearance and surface quality of straight welds as follows:

The welding profile should be good, and both sides of the groove should be covered with a width of 2mm. The height of the welded joint of the fillet weld shall conform to the design specification, and the shape shall be smoothly transitioned.

Requirements for the surface of the welded joint

① No cracks, no melting, slag inclusion, and splashing are allowed.

②The weld surface of steel pipes with a design temperature lower than -29 degrees and stainless steel pipes with a greater tendency to harden shall not be undercut. The weld bite depth of other related materials should be greater than 0.5 mm, the length of the continuous side should not exceed 100 mm, and the total length of the undercut on both sides of the weld should not exceed 10% of the total length of the weld.

③The surface of the weld shall not be lower than the surface of the pipe. The high welding residue is not more than 3mm.

④ The wrong side of the welded joint should not exceed 10% of the wall thickness and should not exceed 2mm.

2. Surface non-destructive testing

The selection principle of the non-destructive testing method for the surface of the straight seam steel pipe: the ferromagnetic steel pipe is selected for magnetic particle testing, and the non-ferromagnetic steel pipe is used for the penetration test.

For welded joints that are prone to hot cracks, an important surface non-destructive test shall be carried out after welding and after heat treatment. For welded joints that have a tendency to delay cracking, the surface non-destructive analysis test should be carried out after the different welding systems have cooled for a period of working time.

The application of surface non-destructive testing is carried out in accordance with the requirements of the standard. The objects and applications of surface non-destructive testing are generally as follows:

① Quality inspection of the outer surface of the pipe.

②Important butt welds for detecting surface defects.

③Important fillet welds shall be inspected for surface defects.

④ Detection of surface defects of important socket welding and jumper tee branch pipe welding joints.

⑤Groove detection of welded joints with high hardening tendency.

⑥ Check the grooves of non-austenitic stainless steel pipes whose design temperature is lower than or equal to -29°C.

⑦ Inspection of double-sided welds after cleaning.

3. X-ray and ultrasonic inspection

The main objects of X-ray inspection and ultrasonic inspection are butt joints of longitudinally welded steel pipes and butt joints of welded pipe fittings.

The weld has a tendency to crack after delayed welding. After cooling for a period of time, X-ray inspection and ultrasonic inspection should be carried out. When the main pipe in the casing has a girth weld, the weld should be 100% X-ray inspected, and the hidden operation can only be carried out after the test pressure is qualified.

The welded joints on the pipeline that can be covered by the reinforcement ring or the support pad shall be subjected to 100% radiographic pass inspection, and then the reuse coverage can be developed after passing the test. The NDT is scheduled to be inspected in the middle of the weld, and the back surface of the NDT is ultrasonically inspected after the appearance of the radiation is checked. The welding can only be continued after the weld has passed the qualification.