Why can’t stainless steel pipes be welded with gas welding?

Plain carbon steel and low-alloy steel have good gas cutting properties； High-carbon steels, as well as medium-alloy and high-alloy steels containing elements that facilitate hardening (such as chromium, molybdenum, tungsten, manganese, etc.), have poor gas cutting properties. Stainless steel contains large amounts of chromium and nickel, which enables it to form oxide films with high melting points (such as Cr2O3). Cast iron has a low melting point, while copper and aluminum have good thermal conductivity (aluminum oxides have high melting points); these are metal materials that are difficult or impossible to cut by gas welding.

What is gas welding? . Could you tell me?

Oxyacetylene welding involves using the high temperature of an oxyacetylene flame for welding tasks.

The gases used in gas welding are oxygen and hydrocarbons. The main problem is that gas welding can cause carbon and hydrogen to penetrate into stainless steel. As we know, carbon reacts with chromium in stainless steel to form carbides, which results in a reduction of chromium content and thus a decrease in the steel’s corrosion resistance. The presence of hydrogen can lead to hydrogen embrittlement. It is essential to strictly control the level of hydrocarbons during stainless steel welding, as they can affect the mechanical properties and the structure of the metal. Carbon arc gouging may be used to clean the root area during stainless steel welding, but this process already causes carbon penetration into the stainless steel; therefore, it is necessary to grind the gouged area afterward in order to remove the carbon-rich layer and reduce the hydrocarbon content in the weld. Gas welding not only fails to achieve the goal of reducing hydrocarbon content, but actually increases it in the weld. Hence, gas welding should not be used when working with stainless steel