Hello ! I have to replace the elbows (90° M/F 3/8 npt) for the blow off valves of my boiler. Has somebody the experience ot using stainless steel fittings on a steel boiler ? Is the difference in thermal expansions a problem ? (On my boiler, these elbows are NOT in the fire, on the bottom plate : they are on the external side, at the bottom of the boiler).
Thank you !

I think most people will say that regular steel is best to keep them tight. Plus, the SS fittings are quite pricey. Get some forged steel hydraulic style fittings and call it a day.

After over thirty years of operating Stanley boilers, I would not use anything different than 1/4" schedule 80 Stainless fittings for my blow down fittings into my bottom tube sheet. Thermal expansion in dissimilar metals is to our advantage here. The greater expansion of stainless as the temperature rises makes the fittings a tighter seal to the steel tube sheet . The schedule 80 is also tougher than the schedule 40, so if the burner is handled roughly, the fittings will not get broken off. Years ago I tried using 1/8" schedule 40 malleable iron street elbows. The iron fittings would only last about three years before they would become so thin from oxidation (rust) that they would start leaking. The 1/8" street elbows were also so restricted that they would often become plugged up with boiler sediment. I buy my stainless fittings from dairy hardware suppliers, or I buy on line from McMaster-Carr. On anything that handles water or steam on my Stanleys, stainless fittings are used where possible. I drive 10, 20, and 30 HP Stanleys and I log about 2,500 miles a year between them. I operate from 450 pounds to about 550 pounds per square inch steam pressure. A Locomobile steamer operating at 180 PSI and not being driven any more that 200 miles of year could get by with a lot less than using schedule 80 stainless in the bottom tube sheet.

I encountered the same problem as SSsssteamer with iron fittings. I decided to use now stainless steel. Thanks for answering !

OOOPS we may need a short discussion on drilling
holes in a high pressure boiler shell,,,
What pressure are you running,,,,
what is the shell thickness
ASSUMING this is a UK car and no wire wrapping,,
OR rivits,,,, ,,,, ,, , , 0
####,,, I also had some stainless that corroded
when used with iron fittings,,I saved them for future
testing,,they were on the racer,,
Cheers,,Ben

Hi Ben,
I am interested in learning more about drilling holes in a high pressure boiler shell. My boiler is USA made 20 in x 14 in with wire wrapping, for a 10 hp Model 63. Made by Alan Kelso.
Thanks,
Alex Beamer

I have never seen that happen Ben but it is very possible. Stainless falls at both ends of the galvanic scale. One end can be passive and the other end active. All nuts and bolts made in stainless in the US are supposed to be pacified. But that does not apply to all products made of stainless steel. You can have a piece of rod or pipe or stainless steel stock and machine one end and change that end from what the piece was originally making it a battery. + and – in the same piece. Corrosion.
I have used stainless fittings in the past but much prefer forged steel and for the boiler Sch 80. The smallest I use on a boiler is ¼ inch.
Rolly