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Air Reciever Corrosion Allowance

Air Reciever Corrosion Allowance

Air Reciever Corrosion Allowance

(OP)
What are the requirements for corrosion allowance in ASME Section VIII, Division 1 air receivers? Non-mandatory Appendix E requires it to be considered by the designer. The codebook index refers to UCS-25 which has been deleted from the codebooks for sometime.

The question was raised when reviewing the calculations from a manufacturer of air receivers that are mass produced. No allowance for corrosion was included in their calculations. (In this particular case the material is SA 455 and SA 414G, both carbon steel).

Any comments and historical perspective on this is appreciated.

RE: Air Reciever Corrosion Allowance

I would expect at least a 1/8" CA allowance in this service from a process engineering point of view.  You may have this already with plate and head thicknesses used compared to the thicknesses you need for the design pressure/temperature.

I wouldn't think that ASME would specify this but I'm not a code expert.

RE: Air Reciever Corrosion Allowance

There is no specific requirement in ASME VIII Div.1 for providing minimum values for corrosion allowance.
However, as corrosion allowance is a concern for the code, I think that a vessel where the manufacturer includes no corrrosion allowance cannot conform to the code, unless the manufacturer can demonstrate, based on operational experience, that no measurable corrosion is detectable for the material of construction and the service of the vessel.
Whereas this would generally be true for stainless steels (though not for all fluids of course), it would be difficult to prove in the case you describe.

prex
motori@xcalcsREMOVE.com
http://www.xcalcs.com
Online tools for structural design

RE: Air Reciever Corrosion Allowance

Note that minimum thk required is 2.4 mm for air and steam service, that if there is thining by corrosion, erosion or mechanical abrasion increase of thk or suitable method of protection is required.
There is a good practices regarding the corrosion allowance in Appendix E of the ASME VIII-I but no values are given.

RE: Air Reciever Corrosion Allowance

The Code does not enforce a corrosion allowance.  It is up to the designer/user to specify an applicable corrosion based on experience with the type of equipment and service.  For air receiver, I would expect at least 1/8" internal CA for typical compressed air.  For instrument dry air, internal CA is not an issue.

Just my thought.

RE: Air Reciever Corrosion Allowance

From my experience, it appears that the zero corrosion allowance on "standard" mass produced air receivers is very common.  So are large diameter threaded connections and lack of adequate manways for internal inspection.  They are "legal" per ASME code, but reflect poor design practices and are this way only to minimize cost.  For these reasons and safety concerns we don't allow this type of air receiver in our plants.  

My advice would be to stick with 1/8" minimum corrosion allowance on all carbon steel vessels, and have no threaded (all flanged) connections.  Additionally, have a real manway that an inspector can use to inspect the vessel.  By the way, you will pay probably at least 2 times as much for this type of custom vessel as compared to the mass produced "junk" variety vessel.

RE: Air Reciever Corrosion Allowance

What's so tricky?  Define the expected service life and multiply by the expected corrosion rate to get the CA.  

Since the corrosion rate of steel in air is zero, that explains why no CA is normally provided or necessary.  

HOWEVER, air receivers can accumulate condensation in the low spots and this can corrode the steel at 5 - 10 mpy so either design to avoid accumulated condensation or add a corrosion allowance in the low spots.  Receivers also have been known to corrode on the exterior, but because that is not predictable, the designer usually ignores this too.  

I believe these are the reasons more conservative owners add some corrosion allowance and settle for 1/8 in.  The code does not care what CA you specify.

RE: Air Reciever Corrosion Allowance

To all,

Rustbuster, as usual, is on the money....Due to the nature of compressed air systems, air receivers commonly collect large amounts of water and are commonly ignored for years.

Failure of air receivers due to internal corrosion is an eventual EXPECTED occurance.

Check the following:

http://os8150.pb.gov.bc.ca/4dcgi/nritem?5300
http://www.osh.dol.govt.nz/order/catalogue/pdfs/slines36.pdf


Every time I go to Sears, I look at on of the little cautionary tags attached to the air compressor/receivers. The tags are required by the US government based on sad experience.

The tag/sticker warns the potential owner about the need to drain his air tank periodically. Or suffer the consequences... Check it out....

Just my thoughts....

MJC

RE: Air Reciever Corrosion Allowance

(OP)
To all-

Thanks for the input! Lots of good practical advice here. I recognize the real world need for providing a corrosion allowance in air receivers, hence my questioning a corrosion allowance of “0” for a pressure vessel sold as an air receiver. It would seem that the manufacturer should hold some responsibility –liability ?- for implying that these pressure vessels are suitable for the service advertised.

By the way, I do know that other pressure vessel codes specify a minimum corrosion allowance, for example Japan requires a minimum of 1mm regardless of the service.

Anyone know why UCS-25 is still referenced in other sections of the code even though it has been deleted?

Thanks again!

RE: Air Reciever Corrosion Allowance

By the way, there is nothing wrong with a zero corrsion allowance, provided that you are WILLING TO RETIRE THE VESSEL ONCE ANY CORROSION IS DETECTED.  Hence, my earlier comments.

RE: Air Reciever Corrosion Allowance

A certain country, renown for its pasta and fast cars, started exporting small air receivers with no corrosion allowance to the UK.  The UK inspection authorities got together and said we are going to increase the frequency of inspection on these vessels because of the increase in risk.  However the department of trade said, careful chaps, you are going to invite the wrath of the European Commission because all these vessels comply with the European Simple Pressure Vessel Directive.  So being good Europeans, they all backed down.

This was several years ago and none to my knowledge have failed.  I suppose corrosion tends to be localised and therefore more likely to cause a leak rather than a catastrophic failure.  

Regards
John www.gowelding.com

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