1.Question: What are the commonly used standards for LSAW Pipe, EFW Pipe, ERW Pipe, and HFW Pipe? (Domestic + International)
1.Answer: Domestic standards: LSAW Pipe follows GB/T 9711 (Pipeline Steel) and GB/T 3091 (Low-Pressure Fluid Transportation); EFW Pipe follows GB/T 13793 (Straight Seam Welded Pipe) and GB/T 8163 (Fluid Transportation); ERW Pipe follows GB/T 3091 and GB/T 13793; HFW Pipe follows GB/T 9711 and GB/T 12771 (Stainless Steel Welded Pipe, if made of stainless steel). International Standards: LSAW Pipe conforms to API 5L (American Petroleum Institute, core standard for pipeline steel) and EN 10219 (Europe); EFW Pipe conforms to ASTM A53 (USA) and JIS G3444 (Japan); ERW Pipe conforms to ASTM A106 and EN 10217; HFW Pipe conforms to API 5L and ASTM A252 (for foundation pipes).
2.Question: What are the non-destructive testing standards for the weld seams of these four types of welded pipes? What items need to be tested for each?
2.Answer: The core testing standards all refer to API 1104 and GB/T 11345. Testing items and priorities are as follows: LSAW Pipe: Ultrasonic testing (UT) is mandatory; thick-walled pipes require additional radiographic testing (RT), focusing on detecting cracks, incomplete penetration, and slag inclusions in spiral welds; HFW Pipe: Ultrasonic testing (UT) is prioritized; high-speed production lines require additional online eddy current testing (ET) to detect minute defects in straight seam welds; ERW Pipe: Ultrasonic testing (UT) is performed; in ordinary scenarios, this can be simplified to surface penetrant testing (PT); EFW Pipe: Ultrasonic testing (UT) + surface penetrant testing (PT) is performed, focusing on detecting porosity and pinholes in precision welds.
3.Question: How is the hydrostatic test pressure for LSAW Pipe calculated? What are the differences in calculation formulas compared to ERW/HFW Pipes?
3.Answer: The formula for calculating the hydrostatic test pressure of an LSAW pipe is: P = 2σt/D (σ is the allowable stress of the pipe, t is the wall thickness, and D is the outer diameter). Because LSAW pipes are thick-walled and large-diameter, the allowable stress is relatively low (usually 70% of the base material strength). The calculation formula for ERW/HFW pipes is the same, but the allowable stress is higher (80%-85% of the base material strength). Furthermore, HFW pipes have better weld strength, resulting in an allowable stress 5%-10% higher than ERW pipes. For example: For a DN500 LSAW pipe (t=20mm, σ=240MPa), P=2×240×20/500≈19.2MPa; for the same specification HFW pipe (σ=280MPa), P=2×280×20/500≈22.4MPa.
4.Question: What are the standards for the outer diameter and wall thickness tolerances of the four types of welded pipes? Which welded pipe has the highest precision?
4.Answer: Outer diameter tolerance: LSAW Pipe: ±1.0% (large diameter) / ±0.5% (small and medium diameter); HFW Pipe: ±0.2%-±0.3%; ERW Pipe: ±0.3%-±0.5%; EFW Pipe: ±0.1%-±0.2% (highest precision). Wall thickness tolerance: LSAW Pipe: ±10%; HFW Pipe: ±5%-±7%; ERW Pipe: ±6%-±8%; EFW Pipe: ±3%-±5%. Overall precision ranking: EFW Pipe > HFW Pipe > ERW Pipe > LSAW Pipe. EFW Pipe has the highest precision among the four and is suitable for precision pipe requirements.
5.Question: What are the bending test requirements for welded joints of LSAW Pipe, EFW Pipe, ERW Pipe, and HFW Pipe?
5.Answer: The bending test is a core test to verify the plasticity and toughness of the weld. The requirements are as follows: LSAW Pipe: 180° face bend and back bend tests are required. The mandrel diameter is 3t (t is the wall thickness). The specimen is considered (qualified) if there are no cracks or delamination. Due to the thick wall characteristics, the mandrel diameter is slightly larger. HFW Pipe: 180° face bend and side bend tests are required. The mandrel diameter is 2t. The specimen is considered (qualified) if there are no cracks, indicating excellent weld plasticity. ERW Pipe: 180° face bend test is required. The mandrel diameter is 2.5t. Slight surface scratches are allowed, and the absence of cracks (qualified). EFW Pipe: 90° face bend test is required (due to the thin wall's tendency to deform). The mandrel diameter is 1.5t. The specimen is considered (qualified) if there are no cracks or weld detachment. This is the least lenient bending test requirement among the four types.
