What grade of steel bolts for boiler casing ?

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ianrichards
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What grade of steel bolts for boiler casing ?

Post by ianrichards » Sat Nov 04, 2017 11:11 am

Considering the temperatures reached, would A4 nuts be sufficient for the inside of the boiler casing?
Also, what Loctite would you recommend?
TIA
Ian
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barts
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Re: What grade of steel bolts for boiler casing ?

Post by barts » Sat Nov 04, 2017 5:26 pm

A4 bolts are what we refer to as 316 stainless in the US. There is also an element of cold work involved to increase the strength,
as 316 isn't heat treatable. The strength varies depending on the grade (e.g. A4-70). The strength drops relatively slowly w/
temperature. The steel portions of the boiler casing will be temperature limited long before these nuts. For example, A4
has a maximum service temp of 815C!

If you're using A4 because of temperature issues, loc-tite is useless - take a look at the release temperature. Use mechanical
retention devices such as lock washers or flange nuts. Note that these devices typically have somewhat lower temperature limits than
the fasteners themselves to presumably prevent high temperature creep & relaxation.

I would definitely use a metallic anti-seize compound during assembly to help prevent galling on assembly/disassembly.

- Bart
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cyberbadger
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Re: What grade of steel bolts for boiler casing ?

Post by cyberbadger » Sat Nov 04, 2017 5:30 pm

A different approach is don't use stainless. Rust which develops makes a very effective sealant and threadlocker.

-CB
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Re: What grade of steel bolts for boiler casing ?

Post by fredrosse » Sat Nov 04, 2017 6:46 pm

"......inside of the boiler casing"

Not clear if this is the casing that forms the insulating layer surrounding the boiler pressure vessel, or a casing that forms the firebox/furnace, or both?

What type of metal forms the parts you wish to bolt together? In general bolting should be the same material.
ianrichards
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Re: What grade of steel bolts for boiler casing ?

Post by ianrichards » Sat Nov 04, 2017 6:49 pm

Both
fredrosse wrote:"......inside of the boiler casing"

Not clear if this is the casing that forms the insulating layer surrounding the boiler pressure vessel, or a casing that forms the firebox/furnace, or both?

What type of metal forms the parts you wish to bolt together? In general bolting should be the same material.
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Re: What grade of steel bolts for boiler casing ?

Post by barts » Sat Nov 04, 2017 8:06 pm

Otter's boiler casing is held together w/ 1/4" 304 or 316 stainless Allen head bolts. I use stainless because I wanted something that wouldn't rust so easily;
it could easily have been grade 5 cap screws.

- Bart
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ianrichards
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Re: What grade of steel bolts for boiler casing ?

Post by ianrichards » Sat Nov 04, 2017 8:35 pm

That’s what I planned on using
Thanks
Ian
barts wrote:Otter's boiler casing is held together w/ 1/4" 304 or 316 stainless Allen head bolts. I use stainless because I wanted something that wouldn't rust so easily;
it could easily have been grade 5 cap screws.

- Bart
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