Galvanized seamless pipes are widely used in high-pressure, low-temperature and corrosion-resistant environments. Mechanical performance, process performance and corrosion resistance are three important indicators to measure the quality of steel pipes, which are also important to ensure the safety of ship navigation. The specification of seamless pipe is expressed in terms of outer diameter * wall thickness in millimeters. So how to control the quality of galvanized seamless pipe from?
According to the flow chart of galvanized seamless pipe production, round steel billets are made into seamless steel pipes through the main processes of perforation, cold drawing/cold rolling, solutioning, straightening and pickling. Each pipe making link complements each other, especially the accuracy and uniformity of temperature control in the hot furnace, which is an important guarantee to ensure that the chemical composition, surface quality, mechanical properties, process performance and corrosion resistance of the finished steel pipes meet the specifications and standards. Here’s a brief look at the process.
The heating furnaces used in the manufacture of galvanized seamless pipes include billet heating furnaces and steel pipe heat treatment furnaces. The accuracy and uniformity of temperature control are two important indicators to judge the quality of the heating equipment, which is an important guarantee of the heating process. Therefore, manufacturers should strictly fulfill the service life and calibration cycle of thermocouples and test the uniformity of furnace temperature.
The development of the heating process for galvanized seamless pipes should take into account the inherent characteristics of the heating furnace equipment, the type and quantity of billets or tubes, and strictly control the heating rate, holding time and cooling rate to avoid cracking, overheating or overburning. Taking the heating of the billet at the piercing stage as an example, considering the low thermal conductivity of stainless steel (i.e. slow heat transfer) and the large expansion coefficient at room temperature, the preheating time in the furnace should be long, and the heating speed should be slow at the beginning of heating to prevent thermal cracking; when the billet temperature exceeds a certain temperature (generally around 850°C), the thermal conductivity and plasticity of the galvanized seamless pipe increases rapidly. At the same time, stainless steel stays too long in the high temperature section, it will produce alpha phase, i.e. ferrite. When the alpha phase exceeds a certain percentage, the metal thermoplasticity will drop sharply. In serious cases, it will lead to perforation failure, and high temperature and long-term insulation will also make the internal grain of galvanized seamless tube coarse. Therefore, in the soaking stage, it should be heated quickly and soaked for a short time.
In addition, attention should be paid to control the regulation of the atmosphere in the furnace to maintain a weak oxidizing atmosphere, which can both reduce the oxidation of the surface of the galvanized seamless pipe and prevent surface carburization.
Nansteel Manufacturing Co.,Ltd is a company specializing in the production of carbon steel pipes, stainless steel pipes, structural sections and pipe fittings. Its products are widely used in nuclear power stations, thermal power stations, atomic power stations, oil and gas, petrochemical, fertilizer, chemical and pharmaceutical fields. With strong technical strength and years of spontaneous service, we provide customers with quality products with economies of scale. For more, please visit: www.nan-steel.com
