ASME PCC-1, O-7 check fail 2

[insider79]

Hi experts,
I’m calculating assembly torque values for 300#, A105 RTJ flange joint with A193-B7 bolting. I’m referring GP42-32 a British petroleum for calculations and values of variables. Calculation results show O-7 check fails thanks to equation O-6, for size 3,4,6 & 8. I’m not sure how to solve this since Sfmax of the flange sets the limit. Any advise will help?

 

[r6155]

Torque is a very inaccurate method. Use stud elongation.
Regards

 

[XL83NL]

r6155, that statement is incorrect. The thing is, it all depends. Some variables that will determine if torque or tension is better, are not provided by the OP.
I can fully recommend the (excellent) free ASME PCC-1 course by HexTech. That will take you through all the pros and cons of both methods and tell you which is likely to be better for which application or situation.

Huub
- You never get what you expect, you only get what you inspect.

 

[r6155]

@ XL83NL
I have a nice experience in the shop manufacturer, with Pressure Vessels for nuclear.(since 1986 aprox), and with the user. (76 Studs diam 220 mm x 2500mm long, in the Reactor)

Example: Torque value is the same for stud 25mm diam 75mm long or 400 mm. Ridiculous.
For stud elongation the length is the input.
Nobody mention about this difference.

Please take a look in ASME PCC-1

Determining the appropriate torque value to apply to a given fastener set can be problematic. The difficulty is not in the formulas themselves but in accurately predicting the all-important friction coefficients upon which the calculations depend.

Regards

 

[XL83NL]

Why is it ridiculous that a 25 mm dia stud has the same torque for a stud of 75 mm length, versus one of the same dia at 400 mm length?
I can imagine there’s a difference between the two, albeit (very) small. Papers I’ve read about research did not show a significant difference, afaik.

You’re correct in that the nut or K-factor is key in determining the appropriate torque.

Huub
- You never get what you expect, you only get what you inspect.

 

[r6155]

I try to be simple.
There are differences.
In my example: for a 400 mm stud the elongation is 0.31 mm and 0.06 mm for 75 mm long.
Yes, this seems to make no sense. but it's correct
I checked it several times at the pressure vessel manufacturer.

Regards

 

[r6155]

@ XL83NL
More information about turn-off nut (similar to torque concept) that depend of bolt length.

https://www.portlandbolt.com/technical/faqs/turn-nut-method/

https://www.aisc.org/publications/steel-standards/rcsc/

FREE

Regards

 

[XL83NL]

I still don’t understand why torque, for a 25 mm stud, would not be the best method to get la proper bolt load. Your argument may be correct or useful but have little relevance to the points brought up.

PS: im not talking structural bolts here, as the OP mentioned PCC-1

Huub
- You never get what you expect, you only get what you inspect.

 

[r6155]

The concept of tightening bolts/studs is the same for all codes, standards, specifications... in this world.
I can't explain more, for me it is very easy to understand. Sorry

Regards

 

[XL83NL]

I can understand your posts are with the best intentions, but you need to provide more details/background than this to make your point, or even help the OP his question.
Simply stating ‘Torque is a very inaccurate method. Use stud elongation. Regards’ isn’t very convincing.

Huub
- You never get what you expect, you only get what you inspect.

 

[LittleInch]

The OP is nor giving enough information as they are using a BP ETP spec and quoting two different formulae, is not saying what those formula are or giving us any numbers. Therefore impossible to answer his question.

As r6155 says, torque to get to sealing force is a variable depending on friction which is notoriously difficult to get right.

R6155, your example looks OK to me. It's the same elongation per unit length so will give the same sealing force. It would vary the number of turns but if the same friction is there would be the same torque for both lengths of stud.

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