310SS Tube Supports in Heaters

[ProjEngr]

We plan to replace some tubesheets in the convection section (1400°F to 1500°F) of a Reformer Unit heater with stainless steel. Someone mentioned that it is standard to use 310SS for these applications. The ASME Section II-D book indicates that 304SS plate has a higher allowable stress than 310SS plate. Is there another reason why 310SS is used more often? Our flue gas has trace amounts of sulfer, but that shouldn't effect 310SS any more than 304SS (PASCC), right?

 

[mcguire]

Both 309 and 310 can stand about twice the stress at 1500F that 304 can. They require 3000ksi to produce 1% elongation in 10,000 hours. It's 1500ksi for 304. In addition their higher chromium and nickel contents enhance their resistance to oxidation and sulfidation to at least twice that of 304 at 1500F and more as temperature increases. There are also some even better proprietary grades if you can deal with limited sources.

 

I was involved in having to replace tubesheet supports in a process heater in the past. The original tubesheet was a cast 25Cr12Ni but due to long deliverability we were required to select the same material in a plate stock and plasma cut out what was required. I don't recall the material designation. If you are required to weld components and concerned of sensatization then stabilized materials offer good resistance.
Is you are concerned of high temperature sulphidation check out the Haynes alloys on site Haynes International for their literature on HR-160 and alloy 556, otherwise ASM Handbook Vol.13 on corrosion is an excellent source to research your concerns.

 

[vinayakumar]

Check temperature limit which 304 can withstand without excessive scaling (high temp oxidation). the limit is around 1600 F. SS310 can go to about 2100 F.