ANSI Flange deformation

[landrover77]

Hi

I have a client whom is concerned about Raised face flange deformation, due to over tightening of bolts. So is keen to define bolting torques to ensure this is avoided.

The application is 300lb RF with fibre gaskets, defining the torque for the required gasket is not a problem. But i'd also like to define the max allowable torque before the flange will begin to deform, this is assuming the bolts (B7) have adequate strength.

I would imagine for a 300lb flange bending occurs only after considerably torque. So i expect the valve will be well beyond our torque requirements.

Do I need to work this out from ASME IIIV? Or are there published figures or simple formula? I have been unable to find published values.

Cheers

 

[desertfox]

Hi

I think the code you work with includes factors for the flange bending, in my opinion there is no need to look at flange deflection if your following the ANSI code, in fact the gasket will be wrecked long before the flange starts to deflect significantly

 

[Ripz]

Agree with desert fox. If your fibre gasket can handle it, your metal flange can handle it.

 

[LittleInch]

Your clients question is not one normally posed and in reality cannot be answered, hence why you can't find any data. The question is how much deflection do you want to calculate?? The flange will "deflect" the second you apply force to it - it's just you can't see it or measure it. Even deflection of 1 or 2mm will probably not be visible to the naked eye, but require a lot of force. I think by "deformation" he means visible deformation, but this is an unreal amount of force and the amount of deflection then depends on his eyesight.... not something that is possible to define, hence not possible to calculate. His question is like saying "how long do I have to stay in the sun to get a sun tan - far too many variables to get an answer and theoretically it's one minute - just you can't see it.

So to be a bit pedantic, the answer to your question "define the max allowable torque before the flange will begin to deform" is 0.1 Nm. it's just you can see it as the deformation will be in microns or sub microns..

Tell the client that what is needed is supervision and QA / QC checks on the guys tightening the bolts to ensure they don't over tighten them beyond the torque settings for the gasket.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[racookpe1978]

NO!

Can I be any more specific? 8<)

There are specific allowed torques for raised face flanges - but, as implied above but needs to be explicitly stated, those torques are NOT for the raised face deformation limits, but for the upper and lower the gasket compression limits BETWEEN the two raised face flanges.

Your client is dead wrong if they exceed the high limit: Their gaskets will not seal properly because they are crushed and mangled (the v-shaped chevrons are squished so far they leak through the V's..
Your client is wrong if they don't compress up to the torque, or go to the torque in one step, not the 3x steps required in the levels required for each flange diameter.
I will not pretend to remember each manufacturer's torque spec's - They are on each website, and packed with box loads of the gaskets as well.

The raised face flange itself, as noted aboove correctly, will bend very very slightly. But if it is torques tight enough to "deflect" by ANY visible amount, then the gasket has been destroyed and will leak.

 

[moltenmetal]

Most torque tables I've seen stop at 60,000 psi bolt stress. B7 yield is over 100,000 psi at room temperature. So around 2/3 of the fastener yield isn't likely to damage an ASME B16.5 raised face flange. Such a torque may, and probably will, damage the gasket, and is unlikely to actually get the joint to seal if it's leaking.

A raised face bolted to a flat face cast iron flange on a pump or valve? Definitely a worry, and no torque table will help you avoid that problem I'm afraid.

Can you damage a RTJ flange by over-torqueing the fasteners? Probably.

 

[donf]

landrover77,

In my industry, the deformation you're asking about is also known as "flange rotation" (not to be confused with the type or direction of rotation provided by a lap joint flange)

As stated above, most fiber or sheet gaskets will be damaged before flange rotation becomes a problem, but there are certain commonly used gasket types, used with common flanges and bolting, where flange rotation is a vaild concern.

Since I have limited knowledge of the subject, I'll refrain from providing any specifics, but I suggest you search the internet for "flange rotation" (Again, discard the references associated with lap joint flanges). There are a number of published studies related to your question.

I always take clients' concerns very seriously. Sometimes it only takes a little education, or reference to induxtry standards or published practices to resolve. Sometimes, further analysis and documentation is required. On occasion, I've learned a valuable lesson.

donf

 

[Andy49]

Gasket manufacturers such as Garlock and Flexitallic have recommended torque tables on their web sites which includes the information whether the bolts are dry, lubricated etc. I would follow those guidelines.

 

[landrover77]

Thanks Gents.
I agree the degree of flange deformation is unlikely to be problematic, when with the allowable range of gasket stresses.
Thanks everybody

 

[XL83NL]

Gasket manufacturers such as Garlock and Flexitallic have recommended torque tables on their web sites which includes the information whether the bolts are dry, lubricated etc. I would follow those giidelines.

Please, dont. Torque values are, als Ive learned, always dependent on the application and service conditions, and are influenced by some 50 variabels. So how can there then be 1 bolt torque value for a, say, flexitallic spwnd gasket in a 900 pound flange, if there's still dozens of other factors influencing that joint and it's required torque?
Sure, maybe there's a general guideline, and I believe that for smaller sizes, there's a lot overlap, which allows for soms standardization. However, there's also a lot of misconception on this subject.

Furthermore, there seems to be a trent to NOT use high bolt stresses, nut to stay low in torque, as I recall from most presentations on BFJ's I heard at last summer's ASME PVP in Paris.

Get some of Warren Brown's papers and Im sure there worth every penny u needed to buy the paper.

 

[Ripz]

Not sure what's the gist of your response XL83NL. Are you saying that we shouldn't use torque charts?

 

[XL83NL]

Im saying not to use pre-determined tables with torque values by manufacturers, as real torque values are dependent on a lot of factors (read previous reply), which can never be covered in 1 table.
There's not 1 torque value for a B16.5 Cl. 900 NPS 4 flange with a flexitallic SPWND gasket. There are dozens, maybe even hundreds of values. Your specific application and service make up the specific torque value, which cant be taken from a simple chart.