Torque of bolts in hot environment (floating head of heat exchanger) 3

[Stefan2211]

Dear All,

I am still looking for a correct answer, which I couldn't find in google, nor from the heat exchanger supplier. I found a lot about "hot bolting" but nothing about the torque required for bolts in hot environment like the flange connection of a floating head.
We have a high temperature heat exchanger with floating head. The shell side is operated at 275 Deg C, tube side is 200 Deg C.
So the bolts of the floating head are actually exposed to 275 Deg C.
Mu assumption is, that the torque of these bolts should be higher than the normal torque since the bolts expand under the high temperature. This is different to bolts outside at the main head.
Supplier refers to ASME PCC-1 ( we do not have it) but admits it is not covering this subject and we should just use the standard torque for the bolt.
Anyone can briefly comment on this?
Thanks a lot guys

 

[LittleInch]

Have you looked at Belleville washers?

Search on ET ams you find things like this

https://www.eng-tips.com/viewthread.cfm?qid=101244

The problem with extra torque is that you either overstressed the bolt when cold or need bigger bolts to get the required force at your operating temperature.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

Also this and follow the links

https://www.eng-tips.com/viewthread.cfm?qid=498

And try searching the welding bonding and fastener forum under structural engineering.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Stefan2211]

Thanks LittleInch,

I will check it out

 

[desertfox]

Hi

Look at this link

http://www.viewmold.com/Products/Te...y and Application/HIGH-TEMPERATURE JOINTS.pdf

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[TGS4]

So long as you are not insulating your flange (you're not, right?), then the bolts will be at a lower temperature. That works in your favour for an elevated temperature bolted flange joint.

There is no such thing as a "standard torque" for bolts based on size. You NEED to go through the ASME PCC-1 calculations to determine the appropriate bolt force, which will then be translated to bolt stress, which you will use in conjunction with your nut factor (based on the lubricant selected) to calculate a torque. The gasket selection is critical in this calculation. You cannot bypass this step because "we do not have it". Either get it or hire someone who can assist you that does have it.

There is a huge problem with the link that desertfox provided you - it doesn't include a gasket! That will make a world of difference in your calculation.

I will note that 275°C is not particularly hot in the grand scheme of things. In many refineries, this would be barely be considered warm service.

 

[desertfox]

Hi

Go to chapter 3 of the book in this link it includes gasket materials and properties and bolt load calculations

https://www.lamons.com/images/lit_reference/Gasket_&_Fastener_Handbook_2016.pdf

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Stefan2211]

Dear TGS4,

I was not precise enough with my description "standard torque". What I actually meant is the torque in the design drawings provided by the manufacturer. However, they did not provided torque for the inner flange connection of the floating head. The submitted the torque later on based on ASME PCC-1 but the value was the same as for the bolts on the outer flange at ambient temperature. That was what made me thinking. Thanks for your input

 

[Stefan2211]

Hi desertfox,

I will go through the files and will pass it on to our mech. department. Thanks a lot again.

 

[BJI]

There is no good guidance for bolting on a floating head, but as suggested, if you use standard torque tables (empirically based) or that calculated from PCC-1 then you will normally be ok and this has been proven to be the case in service, with lower incidents of leakage from floating heads. You should be able to take the bolt loads up relatively high, since the risk of damage to any joint components will be relatively low for floating head configurations.

While your bolts do heat up more than normal under this condition, you also have a smaller transient change in bolt stress due to the lower delta between the tube side and shell side temperatures. The differential pressure across the joint is also lower, due to the confining pressure on the shell side. There should not be any need for Belleville washers (not sure if there ever is..), just high strength bolting with bolt and gasket materials suitable to the process conditions.

 

[Stefan2211]

Thanks all of you,
a little bit less to worry now.