The joint coefficients of welded steel pipes are divided into two zones, one is the welding zone and the other is the fusion zone.


Welding area
After melting the alloyed metal and metal to be filled, it is cooled at the fastest rate. Welding arrangement is as-cast arrangement of liquid metal crystallization, and the components are separated, the grains are rough, and the arrangement is not fine. However, due to the small welding pool, rapid cooling, strict chemical composition control, low carbon, sulfur and phosphorus, the welding chemical composition is adjusted by alloys, making it rich in some alloy elements. Therefore, the function problem of weld metal is not big enough to satisfy the function request, especially the strength should be easily reached.


2. Melting zone
Transition between melt zone and non-melt zone. The chemical composition of the fusion zone is not uniform, and the arrangement is rough, usually rough overheating or rough hardening arrangement. Its function is usually the worst in welded joints. The superheated zone (or quenched zone) in fusion zone and heat affected zone (HAZ) is the thinnest part of the mechanical function of welded joints. According to the stress intensity of the circumferential (initial) film in the cylinder, a formula for calculating the thickness of the cylinder under internal pressure is derived. Therefore, the corresponding welding coefficient should be the longitudinal weld coefficient of the cylinder.