Four non-destructive testing methods for seamless steel pipes

Non-destructive testing is a method of non-destructive inspection of materials, workpieces or components, and its main purpose is to find discontinuous macroscopic defects (such as cracks, pores, inclusions, etc.) in materials, workpieces or components. Commonly used non-destructive testing methods are: ray, ultrasonic, magnetic flux leakage, eddy current, penetration, magnetic powder, etc.

The main features of non-destructive testing: no damage to the inspected object; 100% inspection can be achieved; defects can be found and evaluated accordingly to ensure the quality of materials, workpieces or components; key components can be regularly inspected and even in use. Long-term monitoring to ensure safe operation and avoid accidents; find defects, point out the causes and laws of their formation, and prompt relevant departments to take measures to improve designs or processes to further improve quality, prevent and reduce waste, and reduce production costs.

(1) Ultrasonic flaw detection

Piezoelectric ultrasound mainly inspects longitudinal defects and is used for diameter and thickness measurement; electromagnetic ultrasound can inspect longitudinal and transverse defects. The main levels are C3 (L1), C5 (L2), C8 (L25), C10 (L3), C12 (L4). Among them, C5 is used for cold working high pressure boiler tubes; C8 is used for hot working high pressure boiler tubes; C10 and C12 are used for other purpose steel pipes.

(2) Eddy current flaw detection

Mainly used for surface and near-surface flaw detection. Penetrating eddy current testing mainly detects lateral defects and delaminations. Eddy current can also be used to measure thickness, hardness, strength, diameter and distance. The acceptance level is A and B. The acceptance level A can be used as an alternative method for the hydraulic tightness inspection. The acceptance level B shall be negotiated by both parties and indicated in the contract. The sample tube has drilled holes (through holes) and longitudinal grooves.

(3) Magnetic flux leakage detection

Mainly used for surface and near-surface defects (such as cracks, folds, interlayers, channels, cold insulation, etc.) flaw detection. The acceptance level is divided into L2, L3 and L4 (the groove depth on the outer surface is 5%, 10% and 12.5% of the nominal wall thickness of the steel pipe), and L2.5 is 8%.

(4) Magnetic particle inspection

Mainly used for surface, near-surface cracks and other flaw detection. There are three types of A-type standard test pieces, B-type standard test pieces and C-type standard test pieces. Magnetic particle inspection only detects vertical and horizontal flaws within 400mm of the pipe end.