The medium used for quenching and cooling of seamless steel pipes is called quenching cooling medium (or quenching medium). The ideal quenching medium should have the condition that the steel can be quenched into martensite without causing too much quenching stress.The commonly used quenching media for quenching and cooling of seamless pipes are water, aqueous solution, mineral oil, molten salt, molten alkali, etc.

Submerged arc welding is an important welding method. Its inherent advantages of stable welding quality, high welding productivity, no arc and little smoke make it an important steel structure in the production of pressure vessels, pipe sections, box beams and columns. the main welding method.

Hydrogen embrittlement is usually manifested as a significant decrease in the plasticity of steel, a sharp increase in brittleness, and a tendency to rupture after a period of time under static load (often lower than the σb of the material).

The heat treatment of 35crmo seamless steel pipe generally adopts solution heat treatment, the so-called annealing, and the temperature range is 1040~1120℃ (Japanese standard). It can also be observed through the observation hole of the annealing furnace. The 35crmo seamless steel pipe in the annealing zone should be incandescent, but without softening and sagging.

Inward folding is a common quality problem in the production of seamless steel pipes. It is the irregularly distributed sheet-like folds and spiral-like folds on the inner surface of the steel pipe, and the edges of the defects are mostly serrated. The cause is generally the residual shrinkage cavity and intermediate porosity of the blank.

Spiral steel pipe is a steel pipe with spiral seam, which is made of strip steel coil as raw material, often warmly extruded, and welded by automatic double-wire double-sided submerged arc welding process. Welding is the most common connection method for steel pipes, so how are spiral steel pipes generally welded?