In practice, welded pipes can be used to convey various low-pressure fluids. These products are typically manufactured from Q195, Q215A, Q235A steels, and Q235B carbon steel. They can also be made from 0317‑standard grades such as 6012 and mild steel grade 755, which are easy to weld. After production, welded pipes must undergo hydraulic pressure, bending, flattening, and other tests, while also meeting specific surface‑quality requirements.
Meanwhile, the length and diameter of welded pipes must also meet the requirements of practical applications. Depending on wall thickness, they are classified into ordinary steel pipes and thick-walled steel pipes. Based on the end configuration, steel pipes come in two types: threaded and non‑threaded. For straight‑seam steel pipes, submerged arc welding is typically employed, utilizing filler metal and a granular flux for the process. Submerged arc‑welded straight‑seam steel pipes can have diameters of up to 1,500 mm. The production technologies for such pipes include JCOE forming and continuous submerged arc welding.
Welded pipe
In other words, as production levels continue to improve, the quality and process standards of various welded pipes have also been enhanced. So, what are the acceptance criteria for welded pipes?
1. Straight-seam steel pipes shall be submitted for inspection in batches, and the Group’s approval procedures shall comply with the relevant product standards.
II. Inspection of welded pipes shall be conducted in accordance with the relevant product standards, specifying the inspection items, sample sizes, sampling locations, and test methods. With the purchaser’s consent, hot‑rolled seamless straight‑seam steel pipes may be sampled in batches based on rolling‑mill batch sequences. In the analysis of test results, if any single item fails to meet the requirements of the product standard, the nonconforming batch shall be identified, and twice the original number of samples shall be selected from the same batch for retesting of the nonconforming item(s). If the retest results—covering all applicable test criteria—remain nonconforming, the entire batch of straight‑seam steel pipes shall not be released from the factory.
If the re‑inspection results remain non‑conforming, each welded pipe shall be individually inspected and accepted, or it shall undergo re‑heat treatment (with no more than two re‑heat treatments), and acceptance shall be carried out in accordance with a new batch. Unless the product standard specifies otherwise, the chemical composition of the welded pipes shall be inspected and accepted based on the melt analysis.
