Quality Objection Handling: Pipeline Welding Deformation
>>Case Overview:
A batch of 304 stainless steel pipes purchased by the customer were deformed after welding. The customer believed that the deformation was caused by the asymmetry of the welding stress caused by the thickness deviation of the steel pipe.
>>Case analysis:
After checking first, the nominal thickness of this batch of stainless steel pipes is 10mm, and there is a thickness deviation of 1mm, but it meets the requirements of “GBT14976-2002-Stainless Steel Seamless Pipe for Fluid Transportation”. Although thickness deviation has certain incentives for welding deformation, more reasons are caused by the characteristics of 304 stainless steel.
The thermal expansion coefficient of 304 austenitic stainless steel is about 1.5 times that of carbon steel, but the thermal conductivity is only 1/3 of that of carbon steel. It is prone to large internal stress.
Once the internal stress is not properly controlled, it is easy to deform, and In actual welding, due to the high viscosity of the stainless steel molten pool fluid, welding is difficult, the welding current often needs to be increased when welding, so that the increase in heat input is prone to welding deformation.
If the stainless steel pipe is deformed after welding, it is difficult to straighten it. Therefore, the pre-welding and welding process are the key. For example, you can use fixtures and ensure as little heat input as possible when welding.
>>Processing results:
Thickness deviation does have a certain impact on welding. The author suggests that the thickness of the pipe should be cross-matched when welding so that the welding stress can be evened.
