Bolted flat end / openings - ASME UG-34 and 2-5 Bolt Loads

[Newport2]

Dear all,

for a research project I am designing a Pressure vessel for 8 bar and a small volume. It should be closed by a Bolted Flat End, containing 3 openings. Before taking the reinforcement in consideration (UG-39) the unweakened thickness of the flat head has to be calculated via UG-34. For this the Design Bolt Load W has to be calculated via chapter 2-5 Bolt Loads. For this the Gasket Factors m for Operating Conditions and Minimum Design Seating Stress y from table 2-5.1 have to be used. However I am using a PTFE gasket, and in table 2-5.1 I didn't find any values for m any y of a PTFE gasket. Is it now legitimate to use the manufacturer's values for the factors m and y?

Furthermore, I wonder if one can deduce from chapter 2-5 the bolt loads with which these should actually be tightened. Or should other points be taken into account here? Because that seems inaccurate to me when normally only the standardised values from table 2.5-1 are used to determine the bolt loads.

Sorry for the simple questions, but the field is relatively new to me.

Best regards
Newport2

 

[r6155]

See Flexitallic Gasket Design Criteria.

Regards

 

[SnTMan]

Is it now legitimate to use the manufacturer's values for the factors m and y?

Yes, and always has been. Table 2-5.1 values are non-mandatory. See the General Note.


No. See Appendix S. Further reading can be found in ASME PCC-1.

Edit: r6155 provides a useful reference as well.

Regards,

Mike


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

 

[Newport2]

Thank you for the advice on the additional information.

Another question on Annex S:

"Therefore, an initial bolt stress of some magnitude greater than the design value must be provided."

So the design bolt load W can be exceeded, even if this W was used to calculate the material thickness of the bolted flat head?

Of course of the same time care has to be taken to not exceed the stress in head and bolts:
"Theoretically, the margin against flange yielding is not as great. The design values for flange materials may be as high as five‐eighths or two‐thirds of the yield strength."
"In the other direction, excessive initial bolt stress can present a problem in the form of yielding in the bolting itself [...]"

However, this still does not give a precise indication of the required tightening torque. How does one normally proceed here? Can more precise values be determined in consultation with the gasket manufacturer?

 

[r6155]

@ Newport2
Please read ASME PCC-1, as say SnTMan.

Regards

 

[Vikko]

Fluoro polymer like PTFE (and also FKM, NBR, etc) is an elastomer according to table 2-5.1, thus only the toughness of the material is of importance: if it is below 75 Shore A, m=0.5 and y=0; otherwise m=1 and y=1.4MPa; this at least in case you are talking about a flat circular gasket of constant thickness; but in other case, if you are talking of an o-ring shaped elastomer, whatever the elastomer material is, both m and y are zero.

 

[SnTMan]

So the design bolt load W can be exceeded, even if this W was used to calculate the material thickness of the bolted flat head?

Yes, that and other Apx 2 values are for design of the flange only.

Can more precise values be determined in consultation with the gasket manufacturer?

Absolutely.

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