Welding plays a pivotal role in the manufacturing process of pressure vessels, where materials undergo cold and hot processing, including cutting methods like shearing and flame cutting. The primary method of forming these vessels is welding, with the most commonly employed welding techniques being GTAW (Gas Tungsten Arc Welding) non-melting electrode gas shielded welding, GMAW (Gas Metal Arc Welding) melting electrode gas shielded welding, and SAW (Submerged Arc Welding).
Welding Joint Types in Pressure Vessel Welding
Considering the different components under pressure, welding joints are categorized into four types—A, B, C, and D—according to the “GB150” standard. These joints involve longitudinal joints in cylindrical and conical sections, circumferential joints connecting spherical heads to cylinders, and various joints in convex and flat heads, as well as embedded joints or flange connections with the shell. Each type has distinct characteristics, and their classification is critical for adherence to welding standards.
Welding Joint Classification
- Type A Welding Joint: Includes longitudinal joints in cylindrical and conical sections, circumferential joints connecting spherical heads to cylinders, all splice welds in convex and flat heads, and joints connecting embedded pipes or flanges to the shell.
- Type B Welding Joint: Encompasses circumferential joints in shell sections, joints connecting the small end of conical heads to pipes, joints connecting flanges to the shell or pipes, joints where flat covers or tube sheets connect to cylinders, and circumferential joints between pipes. Excludes joints already designated as Type A.
- Type C Welding Joint: Involves joints connecting hemispherical heads, flat covers, and tube sheets without direct contact to cylinders, joints connecting flanges to the shell or pipes, lap joints between internal heads and cylinders, and longitudinal joints in multi-layered vessel plate layers. Excludes joints already designated as Type A or B.
- Type D Welding Joint: Encompasses joints connecting pipes (including manhole cylinders), flanges, and reinforcement rings to the shell. Excludes joints already designated as Type A, B, or C.
- Type E Welding Joint: Refers to joints connecting non-pressure components.
Read More: Pressure Vessel Manufacturing Process
Welding Preparation and Welding Environment
Before welding, it is crucial to store welding materials such as electrodes and flux in dry conditions with a relative humidity not exceeding 60%. Welding is prohibited under specific environmental conditions, including high wind speeds, extreme humidity, rainy or snowy weather, and temperatures below -20°C. Preheating may be required for welding in temperatures between 0°C and -20°C.
Upon completion of welding, radiographic testing of major pressure welds is essential to ensure welding quality, as per NB/T47013.2-2015.