The steel pipe is divided into seamless steel pipe and welded steel pipe. Among them, the commonly used welded steel pipe can be divided into three types according to the type of weld, such as high-frequency welded pipe(ERW), straight seam submerged arc welded pipe(LSAW) and spiral submerged arc welded pipe(SSAW).
1. Basic requirements for the appearance of straight seam steel pipe welds
Before the non-destructive testing of straight seam steel pipes, the inspection of the weld appearance shall meet the requirements. The general requirements for the appearance of straight seam steel welds and the surface quality of welded joints are as follows:
The appearance of the weld shall be well formed, and the width shall be 2 mm per side over the edge of the groove. The height of the fillet of the fillet weld shall comply with the design regulations and the shape shall be smooth transition.
Welded joint surface
(1) Cracks, unfused, pores, slag inclusions, and splashes are not allowed.
(2) The surface of the weld of the steel pipe with a design temperature lower than -29 degrees, stainless steel and alloy steel pipe with a higher tendency to harden shall not have undercut. Other material pipe weld seam undercut depth should be greater than 0.5mm, continuous undercut length should be no more than 100mm, and the total length of the undercut on both sides of the weld is not more than 10% of the total length of the weld.
(3) The surface of the weld shall not be lower than the surface of the pipe. The weld height is not more than 3mm (the maximum width of the welded joint group to the rear groove).
(4) The wrong side of the welded joint shall be no more than 10% of the wall thickness and not more than 2 mm.
2. Surface nondestructive testing
The selection principle of the non-destructive testing method for the surface of straight seam steel pipe: for the ferromagnetic material steel pipe, the magnetic powder test should be selected; for the non-ferromagnetic material steel pipe, the penetration test should be selected.
For welded joints with a tendency to delay cracking, the surface non-destructive inspection shall be carried out after the welding has been cooled for a certain period of time; for welded joints with a tendency to reheat cracking, the surface non-destructive inspection shall be carried out once after welding and after heat treatment.
The application of surface non-destructive testing is carried out according to the standard requirements. The objects and applications of the objects are generally as follows:
(1) Quality inspection of the outer surface of the pipe material.
(2) Detection of surface defects of important butt welds.
(3) Inspection of surface defects of important fillet welds.
(4) Inspection of surface defects of welded joints of important socket welding and jumper tee branch pipes.
(5) Surface defect detection after pipe bending.
(6) The material is quenched and the groove is detected by the welded joint.
(7) Inspection of non-austenitic stainless steel pipe groove whose design temperature is lower than or equal to minus 29 degrees Celsius.
(8) Double-sided weldment stipulates the inspection of the roots after the roots are cleaned
(9) When the welding fixture on the alloy pipe having the hardening tendency is cut by the oxyacetylene flame, the defect of the grinding portion is detected.
3. Radiation detection and ultrasonic testing
The main objects of radiation detection and ultrasonic testing are the butt joints of straight seam steel pipes and the butt joints of butt welded pipe fittings.
Non-destructive testing methods are selected according to the design documents. For the inspection of welded joints of titanium, aluminum and aluminum alloys, copper and copper alloys, nickel and nickel alloys, the radiation detection method should be used.
For welds with a tendency to delay cracking, the ray inspection and ultrasonic testing shall be performed after the welding has cooled for a certain period of time.
When the main pipe in the casing has a girth weld, the weld shall be operated with 100% ray inspection, and the concealed operation may be carried out after the test pressure is passed.
The welded joints covered by the reinforcing ring or the support pad on the pipeline shall be 100% ray-tested and shall be covered after passing the test.
For welds that require intermediate inspection of welding, non-destructive testing shall be carried out after visual inspection. Radiographic and ultrasonic testing shall be carried out after non-destructive testing of the surface. The welded joints that have been inspected shall continue to be welded after passing the assessment.