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

 

[mech8790]

Hi r6155,

Thanks, I have got a washer in assembly either side.

Regards,
Michael

 

[LittleInch]

mech8790,

You appear rather fixed on trying to use the wrong bolt. Just about everyone else on this thread is telling you it's the wrong thing to do and I will back this up.

If you do some searching around you'll find that use of washers is not universally accepted, in part because of issues like this where someone has tried to use smaller bolts than ones called for and hence put the washer, sometimes of unknown strength, in shear resulting in flange failure.

At the very least, you need to look at the bearing surface of the nut.

A 2" class 1500 flange requires 7/8" (22.2mm) bolts inside a 1" diameter bolt hole (25.4mm). A heavy hex nut is 1.4" (35mm) across the flats.
An M20 bolt on the other hand is 20mmOD inside your 25.4mm hole. An M20 Nut is only 30mm across the flats.

Thus at max movement of the bolt within the flange hole, the edge of your nut is in thin air.
At best (dead centre of the bolt hole), you still have significantly less surface area of the bolt and hence much higher stresses on the nut / flange interface. Add a washer into this mix and all you do is hide the visual issue, but it doesn't add anything to the strength of the joint.

You appear to be asked to verify something which is not possible "I was asked to verify if the bolt size provided in ASME B16.5 is a recommendation or mandatory?" The standard states categorically that bolt sizes are in US customary units - that's mandatory to me.

Replacing bolts is not always easy, but even on a working system, especially if you reduce pressure, replacing bolts one by one can sometimes be acceptable.

You really need to do the right thing here - Use the correct size bolts.


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

 

[r6155]

mech8790

See ASME PCC-1 APPENDIX M
WASHER USAGE GUIDANCE AND PURCHASE SPECIFICATION FOR THROUGH-HARDENED WASHERS

Regards
r6155

 

[A8yssUK]

Hi might be a bit late to the party.

Gasket manufacturer here, please use the right size bolts on standard flanges, as stated for the many reasons above.. it's not just about available force, bolt stretch and yield factors.
Alignment, flange rotation, vibrations, stress distribution etc etc.. using smaller bolts/washers will have an effect... you "might" get away with it... but a class 1500# system means high pressures... so I personally wouldn't risk it.

Only takes one to go wrong and it's your signature on the paperwork.