Corrosion Allowance & Corrosion Rates for various chemicals

[bmoorthy]

Dear experts,

In the mechanical datasheet of equipment, one can see the value for corrosion allowance. When one enquires the mechanical engineer who prepared the datasheet on the basis of providing certain value, reference is made to process datasheet, if you ask the process guys, they refer to client requirement or the feed document or some general thumb rule or philosophy document issued by client, if you enquire the client representative as to how they got the value of CA, they say it is from their previous project or their practice, but no one seems to give convincing reply.

I am looking for ASM or some such publication/standard that gives the list of fluids and expected corrosion rate for a given temperature for various materials for a given flow rate and ph value. While I could ley hand on some of the corrosion rates published, there is no list like the physical properties list for corrosion rate or corrosion allowance.

I request the experts to provide some reference documents, where one can find the corrosion allowances or corrosion rates for fluids encountered in Oil & Gas & refinery for various materials at various Ph values and various temperatures.

Just as one can refer to HTRI for fouling factors and heat transfer values, is there some such institute that will provide the expected corrosion rate of Titanium in 20.2 wt% mixture of Acetic Acid, Formic Acid and water?

Best regards,
B.moorthy

 

[EdStainless]

You can find some data for some specific chemical/alloy combinations.
One real issue is that often it is process specific conditions (temp, flow, impurities) that drive the actual corrosion rates.
But given the range of applications most of it simply needs to be handled as what is reasonable.
Adding CA can have many negative effects (higher cost, more weight, reduced heat transfer, ..) so some prudence is needed.
The first question is will there be corrosion? I have seen CA added in environments where there is no attack.
And then what kind of corrosion do you expect? If it is localized (pitting or cracking) then adding thickness won't help you.
Any operating refinery/chemical plant should have very good information on the corrosion rates within the plant based on inspection histories. When processes are new or modified is ehn real trouble can start.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[MJCronin]

In my opinion, there is a problem here that we can reasonably call "Client datasheet creep"....

In the ASME piping, Boiler and pressure Vessel Codes, a corrosion allowance is specified by the component purchaser and included in the calculation of wall thickness. This is both simple and reasonable... The Corrosion allowance is most often applied to carbon steel components. Client chemical engineers should be aware of their processes and products and have a pretty good idea of how quickly these degrade.

When the corrosion rate is severe, either a corrosion resistant material is specified or resistant coatings are specified. Again this should be explored and specified by those with SPECIFIC EXPERIENCE ABOUT THE PROCESSES OF INTEREST

Since I have retired, the world has gone to hell...

We now have the absurd situation where a "corrosion allowance" must be defined for ANY TYPE OF MECHANICAL EQUIPMENT because datasheets simply get "recopied from the last project, by a group of either monkeys or recent STEM graduates"

Absurd situations like trying to calculate corrosion allowance for fan impellers, valve stems and pipe flange faces arise....... This causes people like the OP to ask if a quickie corrosion "look up sheet" exists

This leads us to the moronic situation where the client's 23 year old "lead engineer" are totally confused because they do not understand the real engineering specification process.

I could be wrong .... does anyone else feel the same way ?

Oh yeah .... and ... HEY YOU KIDS, GET OFF MY LAWN !!!!

MJCronin
Sr. Process Engineer

 

[SJones]

Plenty to chew on here:

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

and it avoids the Millennial Training Manual: Google

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[weldstan]

Shell used to publish corrosion rates for materials in various chemical environments. I believe that ASM Metals Handbook Vol 13 and 13B have incorporated much of the Shell based literature and more. However, many environments have more than one chemical in them.

With regard to corrosion allowance of carbon and low alloy steels, 1/8" was often specified in the 1970s for vessels whether or not the vessel was really in corrosive service but more often 1/16" was specified in the 1980s. For piping 1/16" CA was often selected but even less was specified for power piping by 2015 when I retired. When we applied a 1/4" CA, it most often meant that we expected the material to last through the warranty period but not much more. High alloy and nonferrous alloy pipe was most often specified with no CA.

As Ed stated much of corrosion data is maintained by companies in petrochemical and chemical industries and the real problems show up with changes to the processes.

 

should be explored and specified by those with SPECIFIC EXPERIENCE ABOUT THE PROCESSES OF INTEREST

If I were able to repeat this in bolder face, larger type size or upperer caps I would.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."