How do you metallurgists choose a material?

[FC2008]

I work at a company with no metallurgists, so there is no one to bother with my questions.

The customer often sends me info about Co2 (mol%) and H2S (mol%), along with temperature and pressure and asks what kind of material they should use

The only thing I know how to do is calculate the partial pressure of H2S and select a material from NACE MR0175.

My question is how you pros choose, say a pipe section for use offshore? What type of data is required and which calculations, assumptions etc. must be done?

Thank you.

 

[metengr]

FC2008;
Selection of a pipe run for use in service requires two approaches - consideration of the environment (which you apparently understand as indicated above), and equally as important is the code of construction for the pipeline itself. This code provides specific design rules for determination of minimum wall thickness, allowable stress values for endorsed materials, reactions to consider for the pipe section in service, welding, fabrication and inspection requirements based on design conditions (service temperature and pressure). Are you familiar with any of the ASME piping codes?

 

[SJones]

http://www.google.co.uk/search?source=ig&hl=en&rlz=&q=materials+selection&btnG=Google+Search

Steve Jones
Materials & Corrosion Engineer

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

 

[redpicker]

It's really just a matter of defining the operating conditions and finding a material that will survive those conditions. The devil is in the details.

For mechanical conditions, like torque, bending, axial loading, pressure, etc..., it is fairly easy to calculate the needed strength based on the material strength, the geometry of the component, and the loading conditions. Faitgue is a little more difficult, but it can also be calculated.

For corrosion, it still isn't that difficult, as long as you have enough money. There are materials that are resistant to H2S, CO2, etc..., it's just they are more expensive than low carbon steels. If you need a 100 mile pipeline made out of MP35N, it's going to cost. It would probably be cheaper to buy a fleet of tankers and hire the crews to run them.

The problem is they want the cheapest material that will work. When you finally find a material that will work, it's too expensive and they decide to just go with plain carbon steel (!).

rp

 

[strider6]

http://www.corrosionist.com/Questions_Answers_4_material_selection_oil_gas.htm

S.

Corrosion Prevention & Corrosion Control

 

[FC2008]

Very nice replies. Strider6 : Great link, thank you.