Tighted flange with deformed flat washer

[Steven23144]

Hi,
I have a question, when I tighten the bolts of flange casuse the washer deformation, I don't know if the washer deformation will influence the bolts tighten force.
Does anyone can advise me how to calculate and approve deformation is acceptable.

Steven

 

[TGS4]

Washers shouldn't deform. Either they are not thick enough, or you haven't used through-hardened washers. Or your hole is over-sized for too-thin washers.

Either way, washer deformation should not be acceptable.

 

[Duwe6]

Are the bolts Heavy Hex, or are they 'machine bolts' [wrench = 1.5 * nominal bolt size]?? Are the bolts the correct diameter?
Easy to deform washers when using undersize bolting. The holes in flanges are generously sized, to allow easier alignment for bolt-up. Thus the need [and Code requirement] for heavy-hex bolting.

 

[Steven23144]

We use STUD BOLT 2-1/8" Diameter and 510mm Length with 2 heavy nuts,
Bolts material SA-193-B7, the vessel operating temperture at 300℃
During hydrostatic test @ 25℃ all washer no deformation but when we did hot tightening up at operating condition we found the washer outer rim was rising up
Should we need replace the washer to be more hardness one.
the wash dimemsion: 6t x 56 I.D. x 100 O.D. (mm)

Steven

 

[desertfox]

Hi Steven

What are you tightening the studs too? I guess a torque figure but you haven't stated it, I looked online and found this link below which talks about max bolt service temperature of 371 deg C for the material you stated however it also mentions a bolt tensile stress limit too.
I was just wondering whether you were over tightening the studs?

http://www.portlandbolt.com/technical/faqs/service-temperature-of-a193b7-bolts/

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

 

[r6155]

The use of washer is optional.
Regards
r6155

 

[TGS4]

r6155 - there has not been provided sufficient information to make that judgement. However, in general I (and ASME PCC-1 agrees with me) believe that through-hardened washers are always a benefit.

Stevn23144 - a couple of questions"
1) Are you following a specific procedure for assembly? If so, who wrote it?
2) Why are you hot tightening?
3) Are your washers through-hardened?

 

[r6155]

TGS4 - See ASME PCC-1 "Washers are required only when torquing methods (versus use of hydraulic tensioners) are used for bolt tightening".

Regards
r6155

 

[TGS4]

And washers also have the benefit of increasing the effective length of the bolt. There are a multitude of reasons for using washers. The OP has not provided sufficient information to make any judgements on whether or not washers are required or optional.

 

[r6155]

ASME PCC-1
USAGE:The use of surface-hardened washers is not recommended since the soft interior material under direct compression will flow plastically, causing washer cupping and thinning with associated reduction in preload.

DIMENSIONS:The inside diameter of these washers was selected to enable their use under the nut. Use of these washers
under the head of a bolt may lead to interference with the bolt shank or underhead fillet.

INSTALATION :To avoid any concerns about the effect of washer markings on the performance of the washer to nut interface it is recommended that these washers be installed with the marked face towards the flange surface.

Regards
r6155

 

[GenB]

If you want to fix the problem, Remove the washers.

 

[LittleInch]

steven, see the first posts - you've told us how big the bolts are, how big is the bolt hole??

I agree with the posts which say washer deformation is not acceptable. At the least you need better washers or no washers. I've never liked washers because they are too easily made from incorrect material and often seem to fly under the radar when it comes to specification and testing. Neither B 16.5 nor MSS-SP-44 lists anything to do with washers (neither saying they should or shouldn't be used or providing any material specifications)

If you search under washers on this forum you will find a number of posts which list the requirements if you want to continue using them.

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

 

[desertfox]

Sadly just removing the washers won't necessarily remove the problem because the bearing area of the screw head or nut will be a lot less than the washer and so when the joint is tightened the nut might embed into the flange material.
Member TGS4 stated correctly that we have insufficient information to make a definitive judgment so unless the OP comes back I guess were screwed!

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

 

[LittleInch]

If the nut embeds into the flange material either the nut is far too tight or the flange is not strong enough. Washers are not structural elements and should transmit direct force only, not spread it about. A washer is only a small number of mm thick - any "spreading" of the force from a nut on a pressure vessel is minute and not worth bothering about.

We're talking about TWO INCH diameter stud bolts here. Washers do absolutely nothing at this sort of size.

ASME B 16.5 or MSS SP 44 do not say a single thing about washers therefore they are not required.

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

 

[r6155]

API 660
Hardened washers shall be provided under nuts for all bolts having diameters of 38 mm (11/2 in) or larger.
The washers shall be at least 6 mm (1/4 in) thick.

??????. Incredible !!!

Regards
r6155

 

[LittleInch]

Hmmm, API 660 is a HX spec, but ASME PCC-1 (Guidelines for Pressure Boundary Bolted Flange Joint Assembly) also states washers can be used when torqueing nuts to lubricate the nut flange interface, but at least it has a specification ( ASTM F436-11) and an appendix (appendix M) to follow for said washers which are 6mm thick at that size.

However even this states that washers are optional....

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

 

[desertfox]

Well until we know more about the joint I wouldn't guess as to whether a washer was needed or not.

However if you calculate the bearing area of a 2" nut it's approximately 3.95sq inches and a plain washer for that nut size as a bearing area of 12.35 sq inches, so in my book if that stud/nut is tightened to about 70% of the stud yield stress then the stress on the clamped part without the washer could be 3.15 times that of the joint fitted with a washer,which seems pretty significant to me.

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

 

[Steven23144]

Thanks all specialist to response my question,
We had replaced all washer material into SA-540-B21,
Tighten the Bolts & Nuts with hydraulic bolt tensioning equipment,
eventually no deformation was found.
We guess that maybe the hardness of washer are insufficient or tighten method was incorrect.
I try to calculate the deformation as attachment for reference, you will find the deformation value are small.

 

[desertfox]

Hi Steven

Glad you got it sorted and thanks for letting us know.

There is no attachment with your post

Desertfox

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