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Ultrasonic Testing of ERW Steel Pipe

Date:2022-10-11    keywords: ultrasonic testing, erw pipe
ERW steel pipe is made by using the skin effect and proximity effect of high-frequency current to rapidly heat the edge of the tube blank to the welding temperature and then extrude and weld it. Compared with seamless steel pipe, ERW steel pipe has the advantages of high dimensional accuracy, low price and high production efficiency, and its grain size and structure density are better than seamless steel pipe; compared with the submerged arc welded pipe of the same specification, the production speed of the ERW steel pipe is fast, and there is no local thinning of the anti-corrosion layer at the welding seam. Its application fields involve casings used in oil drilling and production, submarine oil and gas transmission pipes in the offshore oil industry, oil and gas transmission pipes and gas distribution pipes for trunk lines and urban pipeline networks.

There may be many kinds of welding defects in ERW steel pipe, some of these defects come from the base metal, and some are generated in the welding process. Different defects have different effects on welding quality. Area-type defects such as cracks and lack of fusion are prone to stress concentration under stress conditions, which are the main causes of low-stress brittle fracture of welds; while volume-type defects such as pores and slag inclusions are less sensitive to cracking than area-type defects. , However, the effective cross-sectional area of the weld is reduced, and the strength of the weld is reduced. Under the action of external force, these defects often become the source of cracks, which eventually leads to the cracking of the weld.


 ultrasonic testing


Ultrasonic inspection during the production of ERW steel pipes:

Ultrasonic testing is the main non-destructive testing method in the current ERW welded pipe production process. Its main application fields include: 1) Ultrasonic online inspection of steel plate. 2) Ultrasonic online inspection of weld seam after ERW welding and removal of internal and external burrs. 3) Offline inspection of ERW welds. 4) Ultrasonic testing of ERW welded pipe ends.

1. Ultrasonic online inspection of steel plate

Ultra-wave on-line inspection of steel plates generally uses twin or polycrystalline probes, coupled with water film or local water immersion, and its main purpose is to detect layered defects in the steel plate parallel to the surface of the steel plate. There are two main types of scanning methods: one is scanning parallel lines along the rolling direction; the other is that the steel plate moves linearly along the rolling direction, and the probe reciprocates perpendicular to the direction of movement of the steel pipe, forming a "z"-shaped scanning. Since the edge of the steel plate forms a weld in the subsequent ERW welding, the detection of defects at this location is particularly important in the ultrasonic inspection of the steel plate. The relevant standards and specifications require 100% scanning of the edge of the steel plate. In practical work, the method of increasing the number of probes at the edge of the steel plate is generally used to ensure this.

2. Ultrasonic online inspection of welds

The ultrasonic online inspection of ERW weld is carried out after welding and removal of internal and external burrs. It mainly includes two parts: one is to detect internal and external burrs by means of A-scan or B-scan. scraping effect. Compared with A-scan, B-scan can display the inner wall morphology of the weld after removing the internal burr in real time, and the graphic display is more intuitive; the second is the oblique incidence of longitudinal waves, and the shear wave generated by its refraction in the welded pipe is used to detect welding defects. Due to the high temperature of the weld at this time, high temperature probes are generally used for online testing, and local water immersion is used to carry out.

3. Ultrasonic offline inspection of weld seam and pipe end inspection

Off-line ultrasonic testing of ERW welds is generally carried out after hydrostatic testing and chamfering, and is mainly used to detect longitudinal defects in welds and heat-affected zones. In order to improve the detection efficiency, automatic detection is generally used. Due to the influence of the dead zone of the pipe end in the automatic detection. After that, manual ultrasonic scanning of welds is generally added. The content of pipe end inspection mainly includes the detection of pipe end welds, pipe end base metal delamination defects, and axial and circumferential defects. The detection of delamination defects generally uses split probes. The oblique probe scanning method is mostly used for circumferential defects.

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