High Temperature

I would appreciate your thoughts and/or experiences about using weld filler/rod ER 16-8-2, containing 16% (typical) chromium content, vs. ER308H (with ~ 20% (typical ) chromium content in a high-temperature SO2/SO3/Air process at 625C/1157F, to join type 304H stainless steel plate/piping.

  Our goal in considering ER 16-8-2 filler rod is to achieve adequate corrosion resistance to the process, and improved creep strength, and resistance to sigma phase formation, stress relaxation cracking (SRC), and grain boundary carbide precipitation.    

As you may know, credible corrosion literature, Process Industries Material textbooks/resources, and much experience support recommend using alloys/filler metals with a minimum 18 to 20% chromium content for high-temperature SO2/SO3/air processes.   Note: Photographs from service -exposed 304H plate/ER308H weld  in this application showed an apparent thick red/brown-colored corrosion product scale and scale spalling, but no UT thickness information has yet been obtained.   Should I be concerned about potential weld metal corrosion rates (i.e. > 20 MPY) if we use ER 16-8-2 filler rod in this application?

Hello Bill,

Hope you are doing great.  It was nice seeing you are active in AMPP/NACE.

In terms of use of ER16.8.2, the filler wire is considered as a work horse for Hot side of Fluidized Catalytic Cracking (FCC), especially welding of 347 Hexmesh and other component of 304H metallurgy in the hot section of the unit (operating close to 1000 °F [~ 540 °C]).  The lucrative metallurgical property, especially, resistance to sigma phase embrittlement and hot cracking make it preferred material for welding.  Comparatively lower alloy content of 16-8-2 (to 316H or 308), makes it less susceptible to sigma (σ) phase, which enhance the creep ductility in such higher temperature environment.  Also, the lower ferrite content makes it more resistance to solidification cracking (some time referred to as hot cracking).  However, in terms of corrosion resistance, the performance of the 16-8-2 would be similar or say slightly inferior to the 308-filler rod/wire, due to lower total alloying content.

The acid gas SO₂/SO₃ are very corrosive above 1000 °F or above.  In my experience at Sulfur recovery unit (Claus Process, ~1500 °F in incinerator components), the 304 and 310 were not lasting even one TA and ended up replacing 304H and 310 components to Inconel 601.

I can't see the pictures in this blog, however, summarize response to your question, I would suggest using the identical corrosion rate for 16-8-2 to 308 filler wire and if business justifiable, suggest upgrading to Alloy 601 (Inconel® 601).

Hello Bill,

Hope you are doing great.  It was nice seeing you are active in AMPP/NACE.

In terms of use of ER16.8.2, the filler wire is considered as a work horse for Hot side of Fluidized Catalytic Cracking (FCC), especially welding of 347 Hexmesh and other component of 304H metallurgy in the hot section of the unit (operating close to 1000 °F [~ 540 °C]).  The lucrative metallurgical property, especially, resistance to sigma phase embrittlement and hot cracking make it preferred material for welding.  Comparatively lower alloy content of 16-8-2 (to 316H or 308), makes it less susceptible to sigma (σ) phase, which enhance the creep ductility in such higher temperature environment.  Also, the lower ferrite content makes it more resistance to solidification cracking (some time referred to as hot cracking).  However, in terms of corrosion resistance, the performance of the 16-8-2 would be similar or say slightly inferior to the 308-filler rod/wire, due to lower total alloying content.

The acid gas SO₂/SO₃ are very corrosive above 1000 °F or above.  In my experience at Sulfur recovery unit (Claus Process, ~1500 °F in incinerator components), the 304 and 310 were not lasting even one TA and ended up replacing 304H and 310 components to Inconel 601.

I can't see the pictures in this blog, however summarize response to your question, I would suggest to use the identical corrosion rate for 16-8-2 to 308 filler wire and if business justifiable, suggest to upgrade to Alloy 601 (Inconel® 601).