Why are materials of the 13Cr type not allowed to be directly weld-on to valve bodies for valves such as gate valves and stop valves?

To do this, you need to understand the material requirements for the sealing surface: 1, it must be corrosion-resistant; 2, it needs to have the right hardness and wipeability. Welding the base metal is not impossible either; however, adjustments were made after GB was brought closer in line with API. When welding carbon steel directly by surfacing, the challenge lies in controlling the weld fusion zone as well as maintaining the desired hardness level. The real purpose of the replaceable seat in American standards is not actually to replace the seat itself, but rather to ensure reliability in terms of manufacturing processes. For example, what if the hardness of the sealing surface is insufficient? With a separate seat, it is possible to address this issue through heat treatment; this is not feasible with an integral seat. The advantage of stainless steel is that the valve body material possesses corrosion resistance, and its low carbon content makes it easier to control the weld layer as well as the sealing surface. In fact, there are many valve seats that use bulk welding; as long as the welding process is carried out properly, the results will be just as good.

The analysis on the second floor is very comprehensive. The problem of base metal intermixing can be resolved by using multiple weld layers, but post-weld heat treatment cannot be carried out economically. Another advantage of the separate valve seat is that it enables automatic welding as well as various other welding methods, such as plasma welding.

Hello, thank you. You’ve explained things in great detail, but these factors shouldn’t be sufficient to warrant a ban on the use of 13Cr for surfacing purposes; I’m still a bit confused