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Do you normal apply corrosion allowance when designing vessel supports?

Do you normal apply corrosion allowance when designing vessel supports?

Do you normal apply corrosion allowance when designing vessel supports?

(OP)
Hi,

Just a quick one,
Do you normal apply corrosion allowance when designing vessel supports?


RE: Do you normal apply corrosion allowance when designing vessel supports?

No. But I can only speak for the companies with which I have been associated.

RE: Do you normal apply corrosion allowance when designing vessel supports?

Some specs ask for and some never mention.
So appling 1.5mm total and you can forget what will be changed later, making you worry free.

RE: Do you normal apply corrosion allowance when designing vessel supports?

It sounds like a silly, very obvious question, but

"How long do you want the supports hold up the pressure vessel?" and
"What external environment do the legs and support plates have to live within?"

Sure, the dumb things are outside - away from the corrosion (?) of the process fluid itself, and - obviously! - they are not subject to the internal pressure threat if they wear down, BUT they also get exposed to the steady day-to-day corrosion of salt, humidity, sand ?, rain and standing water, galvanic (a little) and the spills and un-removed residue of the process fluid.

Look at the bases and support plates and lower steel of a simple, un-pressurized ash removal tower of even a 15 year old power plant. The steel is 25% gone, and what is left is flaking and spalling, held on by gravity because sandblasting to paint the rust would be even worse. Go to a 40 year plant? The basic steel and braces are even more degraded.

RE: Do you normal apply corrosion allowance when designing vessel supports?

Not unless it is specified.

Regards,

Mike

RE: Do you normal apply corrosion allowance when designing vessel supports?

Spoonful, if you are writing the specification you need to evaluate all the above advice. There are also regulations and recommendations for applying or not corrosion allowance, depending on environment. For eg., in offshore applications or even onshore plants near the edge of the water would need heavy corrosion allowance (unless Duplex or Super-duplex material is used).
In other words, there is no definitive YES or NO answer, but depends on environment. That also applies to the corrosion allowance on anchor bolts.

RE: Do you normal apply corrosion allowance when designing vessel supports?

This was discussed in another forum some time back ( thread1259-173934 ). I posted some numerical results comparing section properties for wide flange legs in new condition and corroded. The loss of strength for such rolled sections can be extremely large (~50%) if the web or flanges are relatively thin...meaning that the corrosion allowance is in the same order of magnitude as these section thicknesses. For heavier sections there is much less effect, but still enough to consider. I think that legs are used more for relatively small vessels, and consequently the support leg sections would be relatively light. And these are the sections that are most susceptible to extreme loss of strength due to corrosion.

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