Answer: Surface cracks are common defects in pressure vessels. In particular, pressure vessels made of low-alloy high-strength steel are more prone to surface cracks. They are the most harmful defects that cause pressure vessels to become unstable. Cracks generated during the use of pressure vessels are mostly surface cracks. Correctly selecting inspection methods and effectively inspecting areas prone to surface cracks are important aspects of ensuring the safe use of pressure vessels.
(1) The welds on the inner surface (including the near-seam area) should be inspected for cracks with the naked eye or a 5-10x magnifying glass.
(2) If any of the following conditions exists, a surface flaw detection inspection of not less than 20% of the weld length should be carried out: material strength grade σb ＞ 540Mpa、Cr - Mo steel with austenitic stainless steel cladding layer; medium with stress corrosion tendency; other suspected welds.
(3) If cracks are found, the inspector should determine the percentage of additional surface flaw detection based on the potential defects that may exist; if cracks are still found, surface flaw detection inspection of all welds should be carried out. At the same time, the possible crack defects on the outer surface welds should be further checked. For the areas where cracks already exist on the inner surface welds, the corresponding outer surface welds should be spot-checked.
