ASME B16.5 bolts

[mech8790]

Hi everyone!

I am looking for some help. I was asked to verify if the bolt size provided in ASME B16.5 is a recommendation or mandatory?
The thing is, the ASME B16.5 states that, for example 7/8'' bolt is required for 1500 RTJ flange but M20 bolt has been used. Is there something that can confirm the M20 bolt is an equivalent of 7/8'' (22.225mm) bolt? I have done the calculations for M20 bolt, but I can't find anything saying that B16.5 bolt size is just recommendation and M20 bolt will work just fine.

Regards,
Michal

 

[TGS4]

Refer to paragraph 5.3.1 and 6.10. Metric bolts are not referred to in the Standard. Substitution would be permitted only in accordance with your Code of Construction, but may require supplementary calculations to maintain the Pressure-Temperature Ratings of the B16.5 Standard.

 

[racookpe1978]

7/8 dia = .875 inch = 22.225 mm.

Yes, a 20 mm bolt "will fit through the holes" - which is why the "bloody idiot" who assembled the joint used that size.
22 mm => 387 area.
Now, 20 mm => 314 area, or 81% of the 7/8 capacity.

So, why would you accept the lower strength bolt?

 

[mech8790]

Thank you for your qucik reply! The whole unit has been designed to ASME Section VIII division 1 which states in appendix 2, par 2-2(e) that minimum bolt diameter is not less than 1/2''.I have done the torque calculations in accordance with formulas in ASME PCC-1 and it looks like the M20 bolt is ok.

Regards,
Michal

 

[mech8790]

The thing is the M20 bolt has been already supplied so I need to proof that it is still ok and there is no need to replace it.

 

[racookpe1978]

You don't understand. It doesn't matter whether a "metric bolt" is allowed or not by a US Code. The bolt installed is only 81% (or less, depending on the material grade used!) of the capacity of the required bolt. Tell them they can use a proper grade metric bolts. As long as it is 22 mm or larger.

 

[MGZmechanical]

Take a look at

https://www.valvesonline.com.au/references/flange-tables/

ISO 7005 PN 20 is, as far as I know, ASME 150 with metric bolts.

Best regards,

 

[KVdA]

I would calculate the bolts as per asme viii appendix 2. If iT passes i wouldn’t worry about it.

 

[SnTMan]

but I can't find anything saying that B16.5 bolt size is just recommendation and M20 bolt will work just fine

Nor will you, I suspect. From B16.5-03:

So, I'd say you cannot use your 1500# flange at the B16.5 pressure-temperature rating.

You may be able to prove it by other means such as Sec VIII, Div. 1, Apx 2.

Regards,

Mike

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

 

[KVdA]

Apparantly I was a bit to quick with my previous answer.
You should also check if BSC=1, using the M20 bolts. If BSC=1 than, in my opinion, you don't need to worry about the flange. A small side note to this is, than actually you still our in the darkish grey area of the code. If you absolutely need to be in full compliance, than you will need to do the full calculation as suggested by SnTman.
Doing the ASME VIII div.1 app2 calc you will come to the conclusion that ASMEB16.5 flanges often are not ok for ASMEVIII app2.

 

[BJI]

Also, you now have over 5mm clearance in your bolt holes which can lead to misalignment and uneven load distribution (only 4 bolts in the small bore size). So even if you do a full design to appendix 2, it still probably isn't recommended. It is not like M20 was used for 3/4", where you could argue it would be acceptable, so IMO I would think the bolts should be replaced.

 

[mech8790]

Hi All,

Thank you all for quick reply. The 2'' flange is 1500# so it has 8 bolts. Obviously, it is easier to say to get 7/8'' bolt but it cost a fortune to replace all these bolts. I have done the calcs in accordance wiith App2 and managed to get the hydrostatic end force per bolt. Than, I have calculated the minimum required torque value using formulas in ASME PCC-1 and maximum torque value that can be applied to the bolt. Results are satisfactory.

 

[r6155]

Torque value is used for installation, not during design calculations.

Regards
r6155

 

[mech8790]

Correct, that is why I have calculated total required area as per ASME VIII div 1 app2, 2-5 and the area of 8 x M20 bolt is still greater than required.

 

[r6155]

Wrong design must be corrected with good design practice.
I disagree with M20 bolts instead of 7/8".
If M20 bolts is used, then two washers are required.

Regards
r6155

 

[mech8790]

Hi r6155,

Can you elaborate why two washers are required?

Regards,
Michael

 

[oknow]

IMO the selection of the bolting is included in the design process for any B16.5 flanges. It should be the duty of the ASME Certificate holder to indicate all the bolting that is to be used for any B16.5 flanges in the remarks section of the MDR. This is a common oversite by many ASME Certificate Holders.If accidents happen in the field the Lawyers may have a field day if it is not recorded on the (legal document) MDR.

 

[SnTMan]

What happened to Michael Kolbuc?

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

 

[mech8790]

Nothing happened, I am still here. Thank, you all for your comments.

 

[r6155]

mech8790
Assemblies often have a slotted or oversize hole: use washer

Regards
r6155