(1) Definition of Stainless Steel Seamless Pipe
A stainless steel seamless pipe is a long piece of steel with a hollow cross-section and no seams around its circumference.
(2) Characteristics of Stainless Steel Seamless Pipes
Firstly, the thicker the wall thickness of the product, the more economical and practical it becomes. The thinner the wall, the more significantly the processing cost increases; Secondly, the manufacturing process of this product determines its limitations: generally, seamless steel pipes have low precision, uneven wall thickness, low brightness on both inside and outside surfaces, high fixed-length cutting costs, and defects such as pitting and black spots that are difficult to remove; Thirdly, its inspection and reshaping must be handled offline. Therefore, it shows its superiority in high-pressure, high-strength, and mechanical structural materials.
(3) Types of Stainless Steel Pipes
According to the rolling method, they can be divided into hot-rolled, hot-extruded, and cold-drawn (rolled) stainless steel pipes.
Based on the different stainless steel microstructures, they can be categorized into semi-ferrite semi-martensitic stainless steel pipes, martensitic stainless steel pipes, austenitic stainless steel pipes, and duplex austenitic-ferritic stainless steel pipes.
(4) Specifications and Appearance Quality of Stainless Steel Pipes
A. According to GB14975-94 "Stainless Steel Seamless Steel Pipes", the standard length (random length) for hot-rolled steel pipes is 1.5～10m, and for hot-extruded steel pipes, it's equal to or greater than 1m. For cold-drawn (rolled) steel pipes, if the wall thickness is between 0.5～1.0mm, the length is 1.0～7m; if the wall thickness is over 1.0mm, the length is 1.5～8m.
B. For hot-rolled (hot-extruded) steel pipes, there are 45 types with diameters ranging from 54～480mm; and 36 types with wall thicknesses ranging from 4.5～45mm. For cold-drawn (rolled) steel pipes, there are 65 types with diameters ranging from 6～200mm; and 39 types with wall thicknesses ranging from 0.5～21mm.
C. Both the inner and outer surfaces of the steel pipe shall not have cracks, folds, fractures, splits, rolled creases, delamination, or scars, and these defects should be completely removed (except for those intended for mechanical processing). After removal, neither the wall thickness nor the outer diameter should exceed the negative tolerance. Other minor surface defects within allowable negative tolerances need not be cleared.
D. Permissible depth of straightness. For hot-rolled and hot-extruded steel pipes, when the diameter is less than or equal to 140mm, it does not exceed 5% of the nominal wall thickness, with a maximum depth of no more than 0.5mm; for cold-drawn (rolled) steel pipes, it does not exceed 4% of the nominal wall thickness, with a maximum depth of no more than 0.3mm.
E. Both ends of the steel pipe should be cut at right angles, and burrs should be removed.