1. Basic requirements for the appearance of ERW straight seam steel pipe welds
Before the non-destructive testing of straight seam steel pipes(ERW pipe), the appearance inspection of welds should meet the requirements. The general requirements for the appearance of straight seam steel pipe welds and the surface quality of welded joints are as follows:
The appearance of welding should be well formed, and the width should be 2mm over the edge of the groove on each side. The height of the welding feet of fillet welds should meet the design requirements, and the shape should transition gently.
Welded joint surface:
(1) Cracks, unmelted, air holes, slag inclusions and splashes are not allowed.
(2) There should be no undercut on the weld surface of pipes with a design temperature lower than -29 degrees, stainless steel and alloy steel pipes with a greater tendency to harden. The undercut depth of welding seam of other materials shall be greater than 0.5mm, the length of continuous undercut shall not be greater than 100mm, and the total length of undercut on both sides of the weld shall not be greater than 10% of the total length of the weld.
(3) The surface of the welding seam shall not be lower than the surface of the pipeline. The residual height of the welding seam is not more than 3mm (the maximum width of the welding joint group to the rear groove).
(4) The wrong edge of the welded joint should not be greater than 10% of the wall thickness and not greater than 2mm.
2. Surface non-destructive testing
The selection principle of the surface non-destructive testing method for straight seam steel pipes: for ferromagnetic material steel pipes, magnetic particle testing should be used; for non-ferromagnetic material steel pipes, penetration testing should be selected.
For welded joints that have a tendency to delay cracks, the surface non-destructive inspection should be performed after the welding is cooled for a certain period of time; for welded joints that have a tendency to reheat cracks, the surface non-destructive inspection should be performed once after welding and after heat treatment.
The application of surface non-destructive testing is carried out in accordance with the requirements of the standard. The detection objects and applications are generally as follows:
(1) The quality inspection of the outer surface of the pipe material.
(2) Detection of surface defects of important butt welds.
(3) Detection of surface defects of important fillet welds.
(4) Detection of surface defects of welding sockets of important socket welding and bridging three-way branch pipes.
(5) Detection of surface defects after pipe bending.
(6) Bevel detection of welded joints with larger material quenching tendency.
(7) Detection of non-austenitic stainless steel pipe grooves whose design temperature is lower than or equal to minus 29 degrees Celsius.
(8) Welding seam of double-side weldment specified rooting inspection after rooting
(9) When oxyacetylene flame is used to cut welding fixtures on alloy pipes that have a tendency to harden, the defects of the repaired parts are detected.
3. Ray detection and ultrasonic detection
The main objects of radiographic testing and ultrasonic testing are butt joints of straight seam steel pipes and butt joints of butt welded pipe fittings.
The selection of non-destructive testing methods shall be in accordance with the design documents. For the detection of welded joints of titanium, aluminum and aluminum alloys, copper and copper alloys, nickel and nickel alloys, the ray detection method should be selected.
For welds with a tendency to delay cracks, the radiographic and ultrasonic tests should be performed after the weld has cooled for a certain period of time.
When the main pipe in the jacket has a girth weld, the weld shall be 100% radiographically inspected, and the concealed operation may be carried out after passing the pressure test.
The welded joints covered by the reinforcing ring or the support pad on the pipeline shall be 100% radiographically inspected, and shall be covered after passing the test.
For the welds required for intermediate inspection of welding, non-destructive testing should be carried out after the appearance inspection is qualified, radiographic and ultrasonic testing should be carried out after the surface non-destructive testing, and the welds that have been inspected can continue to be welded after they are qualified.