How to inspect straight seam steel pipes for non-destructive testing?

Basic requirements for the appearance of straight seam steel pipe welds

 

Before conducting non-destructive testing, the appearance inspection of straight seam steel pipe welds should meet the requirements. Welded joints used for pipe fittings generally require a straight appearance and surface quality, as follows:

 

The weld shape should be good, with a 2mm width covering both sides of the bevel. The shape of the fillet weld joint should have a smooth transition, and the height should also conform to the design specifications.

 

 

Welded joint surface

 

(1) Cracks, melting, slag inclusions, or spatter are not allowed.

 

(2) For steel pipes with a design temperature below -29 degrees Celsius and stainless steel pipes with a greater tendency to harden, the weld surface must not have an undercut. For other related materials, the weld undercut depth should be greater than 0.5 mm, the length of continuous edges should not exceed 100 mm, and the total length of undercut on both sides of the weld should not exceed 10% of the total weld length.

 

(3) The weld surface should not be lower than the pipe surface, and the high slag should not exceed 3mm.

 

(4) The back of the weld joint should not exceed 10% of the wall thickness and should not exceed 2mm. The selection principle for non-destructive testing (NDT) methods on the surface of straight seam steel pipes: Magnetic particle testing is used for ferromagnetic steel pipes, and penetrant testing is used for non-ferromagnetic steel pipes.

 

For welded joints prone to hot cracking, important surface NDT should be performed after welding and heat treatment. For welded joints prone to delayed cracking, NDT analysis and testing should be performed on the studied surface after cooling for a period of time in different welding systems.

Surface NDT should be performed according to standard requirements. The purpose and application of surface NDT are generally as follows:

(1) Quality inspection of the outer surface of the pipe.

(2) Detection of surface defects in important butt welds.

(3) Detection of surface defects in important fillet welds.

(4) Detection of surface defects in important socket welds and tee branch weld joints.

(5) Detection of bevel angles in welded joints with high quenching tendency.

(6) Inspection of grooves in non-austenitic stainless steel pipes with a design temperature below or equal to -29 degrees Celsius.

(7) Inspection of double-sided welds after cleaning.

 

X-ray and Ultrasonic Inspection

 

The main purpose of X-ray and ultrasonic inspection is to inspect butt joints of straight seam welded steel pipes and welded pipe fittings.

Delayed welding increases the risk of weld cracking. X-ray and ultrasonic inspections should be performed after a cooling period. 100% X-ray inspection should be performed on the weld (when the main pipe in the casing has a circumferential weld), and concealed operations can only proceed after the pressure test is passed.

 

Welded joints on pipelines covered by reinforcing rings or support plates require 100% X-ray inspection to pass; only after passing the test can they be developed and reused. Non-destructive testing should be performed in the middle of the planned weld, checking the appearance of the radiation, and ultrasonic testing should be performed on the back side of the non-destructive testing area. Welding can only continue after the weld passes the evaluation.