asme b31 "corrosion allowance value" 1

[Rawya Yasser]

hi all

would please some one help me how to get an exact value for [highlight #FCE94F]corrosion allowance[/highlight] (A) for carbon steel different sizes pipes to use it to get minimum wall thickness

many thanks in advance

 

[BigInch]

It is doubtful that you will find an easy answer to that question. Corrosion allowance is a complicated function of what can be many variables, only a few of which are material(s), fluid properties, temperatures and experience. Best to ask a corrosion engineer, although even that might not give you an acceptable answer.

 

[LittleInch]

The only "exact" value you can get is zero, i.e. when you're transporting something that is inert and non corrosive to carbon steel, say dry natural gas.

Everything else is at best an estimate based on past performance or adaptation of, for example CO2 corrosion. Even then depending on which method you choose you can get wildly varying numbers.

So there are few if any nice simple formulas or numbers, so a lot of piping systems simply apply 0, 1 or 3mm Corrosion allowance depending on the service. If they think that would be inadequate then the materials engineers, who you really should be talking to would normally recommend some other material.

I note you say "B31". B31 encompasses many different codes. Piping for example works one way, but pipelines can often allow for injection of Corrosion Inhibitor and then you get to argue about the "efficiency" of the said inhibitor or indeed how much of the time the inhibitor is able to operate.

Does that give you enough to think about?


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

 

[racookpe1978]

Let us assume yo are junior enough that you honestly do not know.

1. Ask your boss/supervisor/mentor the question: "I have this system (fluid, pressure, operating temperature, duty cycle time in service (if not continuous!), environment, pipe metal alloy. It must serve for 10, 20, 30, 40 years. Where do i look up the required minimum corrosion allowance?"

2. If you do choose NOT to display your courage by asking a well-thought out question after you have determined all of the important variables involved (see above) to the very people who should be telling these things, then WRITE your ASSUMPTIONS clearly at the start of your pipe calculation record.

Assumed corrosion/erosion allowance = 0.062 inch based on assumed ___ (fluid) at ____ (psig) at ____ (degrees F) running for ____ (years) at maximum flow velocity of ____ ft/sec in _____ alloy.

REMEMBER! Do NOT ask them for all of the variables! Be able to ask them (him/her/they/it) for the single answer to the single problem you need AFTER you have found the limitations.

(Likely, it will be in the project specifications (from the client) or from your company's (private) source files for previous projects. )

 

[SJones]

http://www.eng-tips.com/search.cfm?q="corrosion allowance"&action=search

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[europipe]

Don't you use pipespecs? It's mostly mentioned in there.
Fluid, max.temp, max.press. CO , branches etc.

 

[DSB123]

europipe,
Have you ever thought that the OP has been asked to produce a pipe spec???

 

[europipe]

Is that true, Rawya?
The first man in a company to produce a pipespec.?

 

[DSB123]

europipe,
Just for your edification new pipe specs are written everyday by some Companies and as the basis a corrosion allowance needs to be established!!!!

 

[europipe]

Then he should know that the product is the issue, I think.

 

[weldstan]

CA is generally defined by the Engineer/Owner's Engineer based on the corrosivity of the media contained therein on the pipe material and the expected or minimum specified lifetime of the pipe in service. Corrosion rates have been established for many media on a variety of metals and alloys or further established by users' experience derived. It generally ranges from 0 to 1/4" (6.4 mm). In my 45+ years experience, a 1/16" CA has been specified for carbon steel piping systems for Process Piping in the vast majority of cases.

 

[MickMc]

In my experience as part of client team in EPC the CA is defined in the Material Selection Report produced by the Contractor based on the various factors as stated by weldstan. That would be the minimum requirements for each particular service and the Owners more stringent requirements added if relevant. I commonly see up to 6mm in CS and anything required above this would be uneconomical and a more corrosion resistant material used.