How to ensure the quality of seamless black steel pipes?

Seamless black steel pipes are widely used in high-pressure, low-temperature, corrosion-resistant environmental piping systems. Mechanical properties, technological properties and corrosion resistance are three important indicators to measure the quality of steel pipes, and are also important guarantees for the safe navigation of ships. So how to ensure the quality of seamless black steel pipe? According to the production flow chart of seamless black steel pipe, the round billet is made into seamless black steel pipe through the main processes of perforation, cold drawing/cold rolling, solid solution, straightening, pickling and so on. Joint steel pipes complement each other, especially the quality control of raw materials and intermediate products. It is an important guarantee to ensure that the chemical composition, surface quality, mechanical properties, process performance and corrosion resistance of the finished seamless black steel pipe meet the specifications and standards.

To ensure the accuracy and uniformity of furnace temperature control, the following operations can be performed:

The heating furnaces used to manufacture seamless black steel pipes include billet heating furnaces and steel pipe heat treatment furnaces. The accuracy and uniformity of temperature control are two important indicators for judging the quality of heating equipment, and also an important guarantee for the heating process. Therefore, manufacturers should strictly adhere to furnace life and calibration cycle regulations as well as furnace temperature uniformity testing.

The formulation of the heating process should comprehensively consider the inherent performance of the furnace equipment, the type and quantity of billets or seamless black steel pipes, and strictly control the heating rate, holding time and cooling rate to avoid cracks, overheating or excessive combustion. Taking the heating of the tube blank in the perforation stage as an example, considering the low thermal conductivity of the seamless black steel pipe and the expansion coefficient at normal temperature, the preheating time in the furnace should be longer, and the heating rate in the initial heating stage should be very slow. When the billet temperature exceeds a certain temperature (usually around 850 ℃), the thermal conductivity and plasticity of the seamless black steel pipe will increase rapidly. At the same time, if the seamless black steel pipe stays in the high temperature zone for too long, α phase, that is, ferrite, will be produced. When the α phase exceeds a certain proportion, the thermoplasticity of the metal will drop sharply. In severe cases, no holes can be made, and high temperature and long-term heat preservation will make the internal grains thicker. Therefore, the soaking stage in the manufacturing process of seamless black steel pipe should be heated quickly and the soaking should be completed in a short time.

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