Sect VIII Appendix 2 and corrosion allowance 1

[BigTank]

Is there any guidance in the code on what dimensions are to be in the corroded condition and what are not inside of these calculations?

It is difficult to predict the most conserative condition since these calculations are complicated enough to 'bury' the appearant effect of corrosion allowance on the stresses. Sure, I could make a few spreadsheets in an effort to quantify this effects on the flange stresses, but I would think there may be code guidance on this matter.

Does anyone know? I've examined the Compress calculations, and I feel there might be an error in there somewheres, so I'd rather see the code citings if any exist. (My professional side commands I see the print!)

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Fitter, happier, more productive

 

[gr2vessels]

The corrosion allowance normally applies on the thickness of the flange only if it is specified / required by the process design. Remember that the mentioned thickness is measured from the flange face compressing the gasket (the very gasket used to keep the corrosive fluid away from the flange face) to the back of the flange, where the bolt holes might be. The part of the flange which is in contact with the corrosive fluid and is subject to a corrosion allowance, has the thickness simply increased by the amount of corrosion allwance specified. You do however, calculate the flange based on the corroded geometry (Compress, PV Elite and any other PV design software).
Hope this helps,
Cheers,
gr2vessels

 

[tigny]

Hi BigTank,

look at the print, chapter 4.1.4 Corrosion Allowance in Design Equations.

4.1.4.1 The dimensional symbols used in all design equations and figures throughout this Division represent dimensions in the corroded condition.

please have a look also at 4.1.4.2 and 4.1.4.3

yours truly,

tigny.

 

[tigny]

BigTank,

please disregard my first post since it does not answer your question. I'd like to edit or delete if but cannot find the way to do so.

Except for UG-16(e) I don't know of other requirements for corrosion allowance in design formulas in the code, nor especially for Appendix 2. Appendix E has no more information regarding to which dimensions corrosion applies.

As far as corrosion thickness is concerned for flanges with appendix 2
[ol]
[li]I apply a value of internal corrosion thickness to flange bore (B) and (g0) and (g1) for all formulas related to hub thickness. (Table 2.6 and 2.7.1 parameters included)

Except that I don't use internal corrosion thickness for the R dimension (B appears in the calculation of R).

I think external corrosion can be applied to R as well as all other values stated before.

[/li]

[li]
Concerning flange thickness t I apply corrosion thickness on both sides of t (from gasket side to back of flange side). This corresponds to external corrosion.[/li]
[/ol]

If you have access to Code Interpretation it seems there are a few about corrosion allowance so maybe there is an answer to your questions in them.

yours,

tigny

P.S. since you are in flange calculations, may I ask you to have a look at my recent post Hub taper

 

[BigTank]

Thanks Tigny! Only one more question: could you tell me to what book you are referring?

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Fitter, happier, more productive

 

[BigTank]

Ah. Thanks again Tigny. Your last post came in while I was looking through the code and Compress manuals for the print you cited.

Thanks for sharing your methods! It appears that Compress is doing nearly the same thing you are with the corrosion allowance.

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Fitter, happier, more productive

 

[tigny]

BigTank,

incidentely I opened the TEMA 7th edition; in RCB-1.515 it is stated that corrosion allowance shall be applied only to the inside diameter of flanges where exposed to fluids.

yours,

tigny

 

[SnTMan]

BigTank, see UG-25(b), corrosion allowance, if applicable, shall be added to calulated thicknesses.

For Appendix 2, it is common to apply CA to the ID dimensions, B, go, g1, but not the thickness. External CA is uncommon, unless the outides surfaces are exposed to the process, such as internal flanges.

Regards,

Mike