Relatively accurate design temperature for bolts of flanges 1

[mechengineer]

Hello,
Normally, we use the design temperature of pressure vessel as the design temperature of the bolts of flange. However, the metal temperature of shell (directly contact to the hot medium) shall be much different with the bolt temperature by heating transfer (normally being with insualtion on the flange). Does anyone have a simple and acceptable way in engineering to obtain a relatively accurate, suitable design temperature for the bolts of dlange?
Thank you.

 

[desertfox]

Hi mechengineer

The only thing that comes to mind is measuring the actual temperature on the vessel flange or obtain it by a heat transfer analysis using finite difference software or similar.

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

 

[mechengineer]

@desertfox,that way is not my expected, because if design temperature is higher than 350 deg.C all flanges bolts design may need the expensive FEA thermal analysis software.
Thank you

 

[r6155]

@ mechengineer
Where are your ethics?
Many questions reveal your lack of basic concepts, you are very confused and require training,
You abuse experts every day (for free) to do your work, it is offensive.
Do you know the word "PLEASE"?. You never used it, and you rarely use "THANK YOU".
You have no responsibility to work with pressure vessels.

Regards

 

[desertfox]

Mechengineer

In your original post you don’t mention what the design temperature for the application but what you asked was if the bolts and flange were at a different temperature of the main body ie that means you have a temperature gradient between the main body and the flange/bolts however the flange and the bolts are never going to be higher than the design temperature from your application, if the answer isn’t what you expected what answer did you expect? I know of no other way than getting what the temperature of the bolts and flange without performing a heat transfer.
Bottom line is if you assume the bolts and flange are designed for the design temp then that’s a conservative design.

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

 

[SnTMan]

mechengineer, it would be helpful if you had stated bolting materials and class of work and perhaps Code if construction if any. You mention a (design?) temperature of 350 C. A couple of examples for CS bolting: SA-193 B7 (<= 4") allowable is constant to 371 C, SA-193 B16 allowables constant to 426 C. Stainless bolting B8 Cl 2 allowables constant to 454 C.

In these cases there is nothing to be gained by lowering the bolting design temps, the allowables are unchannged.

... if design temperature is higher than 350 deg.C all flanges bolts design may need the expensive FEA thermal analysis software.

I don't understand this statement. It is not necessary, you only to have to design to the allowable stress at the design temperature. You do, of course, have to observe the maximum permitted temperature for the subject bolting material.

As far as calculating a reduced temperature for equipment in the design stage, I'd agree with desertfox, some advanced analysis technique is needed. The cost of such may exceed that saved in the bolting.

Finally, client specifications may mandate the use of the design temperature for the bolting.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[kiad]

see ASME B31.3 301.3.2 in which for uninsulated joints the bolt temperature is considered to be 80% of fluid temperature.
Hope that helps

Regards

 

[Compositepro]

"80% of fluid temperature."

That is a technically meaningless statement. Always beware when a percentage is applied to a temperature. Would that be in Fahrenheit, Celsius, absolute temperature, applied to delta T? I cringe when I hear an engineer say something like an a fluid 100C is at 50% of one at 200C.

 

[mechengineer]

@desertfox, SnTMan,Thanks for the inputs. After reading your treads I tend to design bolts at a design temperature if possible.
@kiad, Compositepro, I will read ASME B31.3 301.3.2. This may be a help if the fluid temperature exceeds the maximum temperature of the allowable stress within 20% of fluid temperature for uninsulated case.
The actual case for a quotation is that a low temperature application (MDMT=-39 deg. C), SA-320L43, bolt size 3", The maximum temperature of allowable stress is 204 deg.C, but the design temperature is 332 deg.C, any suitable bolt material for such case? Thank you.

 

[SnTMan]

mechengineer, you don't mention your Code, but under Sec VIII, Div 1 SA-193 B7 has an MDMT w/o impact testing of -40C in that diameter.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TGS4]

Insulating flanges is not best practice.

I agree that the % of temperature rule is physically meaningless, unless it is accompanied by a specific units (preferably absolute temperatures).

 

[mechengineer]

@TGS4, I agree.
@SnTMan, Design Code is VIII-1. I will inform the customer to change SA-320 to SA-193B7 for the bolt material. Thank you.

 

[r6155]

@TGS4
Please see OSHA 1910 heat-insulating material or otherwise properly guarded.
OSHA does consider exposed heated surfaces, if there is a potential for injury, to be a hazard and will issue citations if employees can come into contact with such surfaces. While there are not any OSHA standards, except those that are applicable only to specific industries, which address exposed heated surfaces, there are several OSHA general standards which address such hazards.

Bolts may be required re tightening during service at 350ºC, hence insulation must be designed for such removal and reinstalling.

Regards

 

[TGS4]

Alternative personnel protection should be provided - insulation on hot flanges is NOT best practice. Removable (frankly any) insulation around a flange has the potential for flash fires, especially if the service in the pipe contains hydrogen. Retightening in-service is also not ideal.

 

[KevinNZ]

Insulation of flanges and valves is common in steam service. Is the concern only about fire risk?

 

[r6155]

@TGS4
You do not mention any Standard or any phrase as follow, can you please?

4.2.1.4 Covers shall be fabricated to allow easy access to valve packing glands and flange bolts without having to completely remove the cover - HOT INSULATION SERVICE UP TO 538ºC

Regards

 

[TGS4]

Speaking of not referencing standards, any chance you'd like to share where that little tidbit comes from?

I've talking with burn victims who were injured when the hydrogen that accumulated under flange insulation combusted instantly upon contact with the air (burns in the ultraviolet spectrum, so you can't even see the flame). Insulate flanges at your own (and your people's own) safety risk.

 

[BJI]

Is the concern only about fire risk?

Is that not a suitable concern?

I would second that it is generally not recommended to insulate flanges. Mesh personal protection can be placed around HT flanges without risk of accumulation of fugitive emissions. Insulating flanges will also affect the relative temperatures of the components, increasing bolt elongation and lowering gaskets stress, possibly leading to more significant joint leakage during upsets or after prolonged service. Insulation of bonnet covers for valves is not the same thing, if that is what r6155 was referring to.

 

[r6155]

@TGS4
"Speaking of not referencing standards" ....ummmm!!, this is very risk
Speaking without a prior reading of the standards is not good practice

1) Bolt tightening--

ASME PCC-2 2018 and ASME PCC-1 2019
Differential thermal expansion may cause a loss of bolt
load during the cooldown of hot flanges (see ASME PCC-1, section
12). This should be considered in determining the hot reassembly
bolt load. In addition, consideration should be given
to allowing replacement bolts to reach their operating temperature
prior to final tightening


2) Thermal insulation of flanges
Process Industry Practices
PIP INSR1000 july 2019
Installation of Flexible, Removable/Reusable Insulation Covers for Hot Insulation Service

Regards