In general; when joinning Grade P91 with SS316, we will need to "butter'' the 91 grade steel with two~three layers of overlapped beads of weld metal; allow to cool slowly, and give a PWHT to soften the HAZ that you have created [WPS; preheat of 200°C for welding, and a subsequent post-weld heat treatment (PWHT). The PWHT temperature depends on the application, but is commonly of the order of 760°C for pipe and 680°C for a heavy section fabrications such as turbine shafts. The duration is usually one hour per 25mm of (maximum) section thickness]. The buttering can use a Ni-base weld metal, {e.g. Inconel 625 type}. and later use the same consumable to join to the SS316 L stainless steel. TCare should be taken when depositing weld metal on the 91 grade side to avoid penetrate deeply into the buttering layers.
However, would the following be possible:
1. Using modified 9Cr-1M0 modified consumable (in accordance to our existing procedure of joining P91 material; i.e. preheat and interpass temperature control of 200°C for welding, control weld cooling down when completed welding and a subsequent post-weld heat treatment (PWHT). The PWHT temperature is heating up at 100°C/Hr after 350°C to 740°C (±20°C) for pipe for minimum of 2-Hrs and for heavy section, additional duration is apply usually one hour per 25mm of (maximum) section thickness. Cooling down with 150°C/Hr until 350°C and leave for air cooling) to "butter'' bevel on the 91 grade steel with two ~ three (note: to avoid penetration of subsequent welding layer using other consumable) layers of overlapped beads of weld metal; allow to cool slowly, and give a PWHT to soften the HAZ ,
2. Using E309L consumable to join the beveled and machined P91 to the SS304 (pipe / valve material) without preheating and PWHT to avoid sensitizing but with control interpass temperature <200°C).
3. Take care when depositing weld metal on the 91 grade side that you do not penetrate deeply into the buttering layers.
4. NDT (RT & PT) and hardness test (<250HB) as require.
Any expert expereince on carrying out this P91 & SS316 / 304 and comments from the Forum are welcome. Thank you.
Welding Of P91 to SS316 / SS304 Material
Re: Welding Of P91 to SS316 / SS304 Material
