This type of spiral steel pipe is used in areas with temperatures exceeding 350°C. Considering the stress relaxation of steel at high temperatures, coarse-grained killed steel must be taken into account. To better transform the martensite crystal specification into coarse grains, silicon-iron deammoniation is necessary. The production methods for spiral-welded pipes include spiral welding and arc welding control methods. The fourth method (STPT49) is only specified for the production method of seamless pipes.

Regarding the heat treatment process, heat pipes do not require heat treatment. Cold-rolled seamless pipes and welded steel pipes must undergo quenching and tempering. The dimensional tolerances for diameter, thickness, and partial thickness are the same as those for high-pressure pipelines. The specifications and models are the same as those of second-class pressure vessels. Due to the thicker wall thickness, the 100, 140, and 160 specifications have been upgraded. Pressure tests are conducted according to the standard numbering.

High-Temperature Stress Relaxation refers to the release of working pressure inside spiral-welded steel pipes under ultra-high pressure. Under high-temperature standards, there should be a capacity between the working pressure of the material and the working point. However, it is not known that after tens of thousands of hours, stainless steel plates will slightly stretch and expand, leading to cracking. This type of condition is known as high-temperature stress relaxation. It is difficult for coarse-grained killed steel to produce this stress relaxation condition. Although these pipes are high-temperature spiral-welded steel pipes, spiral-welded steel pipes are made of carbon steel with a temperature limit around 450°C. If the temperature exceeds 450°C, carbon steel pipelines containing elements like CrMo must be added.