How to ensure the quality of black steel seamless pipe?

Posted by chase Liu on April 7th, 2023

Seamless black steel pipe is uncoated steel, also known as black steel pipe. The dark color comes from iron oxides that form on its surface during the manufacturing process. When steel pipe is forged, a black oxide scale forms on its surface, giving it the finish seen on this type of pipe.

Black steel seamless 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 safe navigation of ships. So how to ensure the quality of black steel seamless pipe? According to the production flow chart of black steel seamless pipe, the round billet is made into black steel seamless pipe through the main processes of piercing, 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 black steel seamless pipe meet the specifications and standards.

In order to ensure the accuracy and uniformity of the temperature control of the heating furnace, the following operations can be performed:

The heating furnaces used to manufacture black steel seamless 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, the manufacturer should strictly abide by the service life and calibration cycle regulations of the heating furnace, as well as the furnace temperature uniformity test.

The formulation of the heating process should comprehensively consider the inherent performance of the furnace equipment, the type and quantity of the billet or black steel seamless pipe, 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 piercing stage as an example, considering the low thermal conductivity of the black steel seamless pipe and the expansion coefficient at room 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°C), the thermal conductivity and plasticity of the black steel seamless pipe will increase rapidly. At the same time, if the black steel seamless pipe stays in the high temperature zone for too long, it will produce α phase, that is, ferrite. When the α phase exceeds a certain proportion, the thermoplasticity of the metal will drop sharply. In severe cases, holes cannot be drilled, and high temperature and long-term heat preservation will make the internal grains thicker. Therefore, the soaking stage in the manufacturing process of black steel seamless pipes should be heated rapidly, and the soaking should be completed in a short time.