In your case ASME B31G would not be the right code. B 31G is an excellent code primarily developed for fitness for service evaluation of above and underground hydrocarbon pipelines(liquid or gas). The fitness margins in these codes will not necessarily be the same for above ground process piping where failures could be catastrophic.
A combination of API-570 and API/ASME -579 would enforce better integrity and remaining life of corroded process plant piping. If it is one to time fitness for service evaluation for corroded pipes API-579 is the ideal code. One can perform Level-1, Level-2 and Level-3 design calculations and validate the remaining life of any component, e.g. pressure vessels and pressure piping. Level-1 & Level-2 is formula based calculations, with different levels of safety margins, Level-3 is calculation plus the FEA analysis.
For long term corrosion and Plant life , corrosion inspection programme as per API-570 would be recommended.
API-579 was originally developed for oil and gas industries. ASME adopted this code in 2007, as post construction code. I attended few trainings with API in 2006/2007, and use this code for component integrity purpose whenever the need arises.
I have attached some extracts from ASME B-31G and API/ASME-579 and API-570 for your reference.
Feel free to raise any question.
Pradip Goswami, P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
[mailto:firstname.lastname@example.org] On Behalf Of hpi001
Sent: Monday, August 02, 2010 3:51 PM
To: Materials & Welding
Subject: [MW:6265] Re: Application of B31G - Strength of corroded Pipe
In my opinion you are correct, the minimum allowed wall thickness is the nominal wall thickness including manufacturing tolerances, minus the corrosion allowance which is taken into account during design calculation.
I'm not that familiar with ASME but when pressure vessels and / or piping are designed under the European Pressure Equipment Directive the minimum thickness never is allowed to be less than the value taken into account during calculations.
However if ASME B31G is applicable to the existing piping and you can guarantee proper and safe operation by way of calculations given in this ASME part and based on the wall thickness found during actual measurements than I would say way not using that possibility to extend the piping's lifetime.
On 2 aug, 14:05, "Pisat, R. (Rahul)" <Rahul.Pi...@akzonobel.com>
One of plant project engineer has asked me to make document for Minimum required wall thickness for the piping which is acceptable to run the process with defined design condition under corroded condition.
As per my understanding this the same Min. wall thickness based on calculation of required wall thickness for design pressure and design temperature .i.e. Min. wall thickness which is ( Nominal wall thickness - manufacturing tol..- Corrosion allowance ).
But one of our old engineering manual has listed the use of ASME B31G manual for determining the remaining strength of corroded Pipelines, after reading this manual , I can state that this manual gives the strength of corroded portion of the pipeline. Defined parameters in this specification is based on Depth of corrosion and length of the metal loss.
My query is how can I use this ASME B31G for defining the minimum required wall thickness requirement for existing piping network in plant.
Do you agree that my initial assumption of Min. wall thickness i.e. Nominal wall thickness - Mfr. Toll. - Corrosion allowance is a right approach ?
Waiting for your suggestions.
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