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Precision stainless steel pipes are highly distinctive in terms of specifications and appearance. Firstly, the thicker the wall of this type of stainless steel pipe, the higher its cost-effectiveness and practicality; conversely, thinner walls significantly increase processing costs. Furthermore, the performance limitations of stainless steel pipes depend on the processing technology. Seamless steel pipes typically have lower precision, uneven wall thickness, lower surface gloss on both the inner and outer surfaces, and higher fixed-length costs. They are also prone to pitting and black spots on the inner and outer surfaces, which are difficult to remove. Additionally, the inspection and shaping of precision thick-walled stainless steel pipes must be done offline. Therefore, stainless steel pipes demonstrate significant advantages in high-pressure, high-strength mechanical structural applications.
Stainless steel pipes are mainly classified according to their rolling process into hot-rolled, hot-extruded, and cold-drawn (rolled) stainless steel pipes. Based on differences in metallographic structure, they are mainly classified into semi-ferritic semi-martensitic stainless steel pipes, martensitic stainless steel pipes, austenitic stainless steel pipes, and austenitic-ferritic stainless steel pipes.
According to specifications, stainless steel pipes are mainly regulated by GB14975-94 "Seamless Stainless Steel Pipes". Precision thick-walled stainless steel pipes generally have lengths (not fixed) of 1.5-10m for hot-rolled pipes and 1m or more for hot-extruded pipes. Cold-drawn (rolled) stainless steel pipes have wall thicknesses of 0.5-1.0mm and lengths of 1.0-7m; those with wall thicknesses greater than 1.0mm have lengths of 1.5-8m.
Hot-rolled (hot-extruded) stainless steel pipes have approximately 45 diameter models ranging from 54-480mm and approximately 36 wall thickness models ranging from 4.5-45mm. Cold-drawn (rolled) stainless steel pipes have 65 diameter models ranging from 6-200mm and 39 wall thickness models ranging from 0.5-21mm.
The inner and outer surfaces of precision thick-walled stainless steel pipes must be free from defects such as cracks, folds, fissures, roll folds, delamination, and scale. These defects must be completely removed (unless the pipe is specifically intended for machining), and the wall thickness and outer diameter must not exceed the negative tolerance after removal. Minor surface defects that do not exceed the allowable negative tolerance do not need to be removed.
The allowable depth of straight sections in stainless steel pipes is also subject to requirements. For hot-rolled and hot-extruded steel pipes, and stainless steel pipes with a diameter less than or equal to 140mm and not exceeding 5% of the nominal wall thickness, the depth must be less than or equal to 0.5mm. For cold-drawn (rolled) stainless steel pipes, the depth must not exceed 4% of the nominal wall thickness, and the depth must be less than or equal to 0.3mm.
Finally, it is important to note that precision thick-walled stainless steel pipes must be cut at right angles at both ends and burrs removed from the pipe wall before application.
