What should be noted during the hot working of spiral steel pipes?

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2021-04-29

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If oil adheres to the surface of a spiral steel pipe during heating, the oxide scale in the oily areas will differ in thickness and composition from that on other parts, and carburization may occur. The base metal beneath the oxide scale that has undergone carburization will be severely attacked by acid. Oil droplets sprayed from heavy‑oil burners at the start of combustion can also have a significant adverse effect if they land on the workpiece. Similarly, operator fingerprints left on the workpiece can cause problems. Therefore, operators should avoid directly touching stainless‑steel components with their bare hands and must prevent the workpieces from becoming contaminated with fresh oil or grease. All handling must be performed while wearing clean gloves.

　　 Spiral steel pipe If oil adheres to the workpiece surface during heating, the oxide scale in the oil‑contaminated areas will differ in thickness and composition from that on other regions, and carburization may occur. The base metal beneath the oxide scale that has been carburized will be severely attacked by the acid. Moreover, oil droplets sprayed from a heavy‑oil burner during initial ignition can have a significant adverse effect if they land on the workpiece. Even operator fingerprints left on the workpiece can cause problems. Therefore, operators should avoid direct hand contact with stainless steel parts and ensure that the workpieces do not become contaminated with fresh oil. All operations must be performed while wearing clean gloves.

　　If the workpiece surface contains lubricating oils or other residues from cold working, it must be thoroughly degreased in trichloroethylene or a caustic soda solution, rinsed with warm water, and then subjected to heat treatment.

　　Precautions for Hot Working of Spiral Welded Steel Pipes

　　If the surface of a spiral steel pipe is contaminated with foreign matter—especially organic substances or adhering scale—the heating process will inevitably affect the oxide scale. Variations in the furnace atmosphere, particularly in different zones, can lead to uneven oxide‑scale formation, which in turn contributes to non‑uniform pickling results. Therefore, during heating, it is essential that the atmosphere be uniform throughout the furnace; to achieve this, proper circulation of the furnace atmosphere must also be ensured.

　　Furthermore, materials such as bricks and asbestos used to construct the fixtures for heating workpieces, if they contain moisture, will release water vapor during heating. This leads to differences in the atmosphere between the portions directly exposed to steam and those that are not, resulting in variations in scale formation. Therefore, any material in direct contact with the workpiece must be thoroughly dried before use. However, if such dried materials are left at room temperature in high-humidity conditions, moisture may still condense on the workpiece surface. For this reason, it is recommended to dry these materials immediately prior to use.

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