There are two main methods for representing the diameter of national standard spiral steel pipes. One is to directly represent it through the outer diameter and wall thickness, and the other is mainly to represent it through the nominal diameter (DN). The method of representing the outer diameter is very simple. The outer diameter of spiral steel pipes is determined by their size. Currently, the most common ones include 219mm, 273mm, 325mm, 426mm, 529mm, 630mm, 720mm, 820mm, 920mm, etc.
The nominal diameter is the universal diameter for various pipes and pipeline accessories. It is not the actual outer diameter or inner diameter of the pipeline, although its value is relatively close to or equal to the inner diameter of the pipeline.
Density test: For welding containers that store liquids or gases, non dense defects such as penetrating cracks, porosity, slag inclusion, incomplete penetration, and loose structure in the weld seam can be detected through density test. The methods for density testing include kerosene test, water loading test, water flushing test, etc.
Each steel pipe pile should undergo a hydrostatic test without any leakage during the hydrostatic test. The test pressure should be calculated according to the formula P=2ST/D, where S is the test stress in MPa for the hydrostatic test. The test stress for the hydrostatic test should be selected based on 60% of the minimum yield value specified in the corresponding steel strip standard (Q235 is 235Mpa). Pressure stabilization time: D<508. The test pressure should be maintained for no less than 5 seconds; D ≥ 508. The holding time of the test pressure shall not be less than 10 seconds. Non destructive testing shall be conducted on the repair welds of steel pipes, butt welds of steel strips, and circumferential welds using X-ray or ultrasonic testing. Spiral welds on steel pipes used for transporting flammable ordinary fluids should undergo 100% SX ray or ultrasonic inspection. Spiral welds on steel pipes used for transporting ordinary fluids such as water, sewage, air, and heating steam should undergo X-ray or ultrasonic inspection sampling (20%).