Steel grade advice for high temp thread application

[USAeng]

parameters: steel is reaching an estimated 800-1000F in a utility boiler... the part with the threads is about 2-3" long and sprays oil into the boiler, the threads are 1 1/4-12 NF class 1B threads and the threading is about 1/2" long

right now we are using 1144 stressproof steel because someone found that the chemistry of the competitor's steel was (in %)
.5C, 1.6Mn, .012P, .27S, .23Si, .03Cr, .02Ni, <.01Mo, .03Cu, <.01Pb, Balance Fe

Now they somehow from that figured that the steel was 1144 stressproof... I assumed they would also need a hardness test?

We tried stainless steel but it galled terribly I guess so they went to thie 1144 but I they are saying there is still a problem getting the threads apart after the parts are in service for a while. I think they are wanting to stay away from the stainless steel. Perhaps I can try stainless again if I can come up with some idea to make it work better.

Is there a material or material combination that I may want to look into that will not tend to seize up at the threads after being in service for extended amounts of time under these conditions? Perhaps the answer is more in the threading? Thanks for any input.

 

[stanweld]

ASTM A-193 B16.

 

[USAeng]

I should also have mentioned that the internal threads are 1 1/4-12 1B UNF and the external threads are 1 1/4-12 UNF with a pitch dia limit of 1.193/1.194

I will look into that b16 material

 

[StoneCold]

Do you put antisieze on them? All of these look like they handle the temperature range you want.

http://www.grainger.com/Grainger/ww...e=true&toolbar=true&CatPage=3099&Catalog=main

 

[unclesyd]

Here is an excellant high temperature thread lubricant (Therm-O-Plate 220} that I've used for similar services.

One thing that might help is to take the tips of the threads off. Doing this will not take away the effectiveness of the thread sealing.

http://www.socousa.com/home/Chemola/Maint/tp220.htm

 

[USAeng]

if we want to use B16 can you order it in 1 1/4" bar stock and machine it?

 

[EdStainless]

Look into 2.25%Cr alloys (F22).
As has already been suggested, Knock off the thread tips and use a Ni anti-seize.
Also look at coarser threads, they will be more robust.

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Plymouth Tube

 

[USAeng]

New update... just was informed that the customer has temperatures that are ranging from 1300-1500F... what does not make sense is that they have product in the area made of alloy carbon steel that seems to last. Does 2.25Cr steel last ok in that temp?

 

[TVP]

USAeng,

EMJ is one supplier that offers a wide range of sizes of hot-rolled bars in grade B16 (ASTM A193). Use the following link for more information:

http://www.emjmetals.com/products/s...sc=Bar&FamDesc=Round&MatDesc=Commercial Alloy