Positive material identification (PMI) on Alloy Steels 1

[Delikado]

Dear Experts,

I would like to get your professional opinions/answers with regard to subject.

According to Russian Regulation:

"Positive material identification shall be performed for all welded joints of alloy steel pipelines of Category I, or
transporting media of Group A(a), or operating under PN > 100."

currently there is a discussion as to which specific materials are required because to say "alloy steel" means it includes even carbon steel.

The engineering contractor says it should only be materials with high alloy and Nickel based materials operating at high temperatures.

Our materials in the project are P91, P11, P22, 304L,316L,321 and LTCS.

Engineering contractor specify that only P91 and the Nickel based materials requires PMI but client told to include P11 and P22 because these are also alloy steels.

To perform PMI on these welds is not an issue but my question is, does the engineering company's stance about to which extent PMI application is required, somehow reasonable (high and nickel based alloys)? (if any body could give reference about it is highly appreciated).

I know that client's decision to include low alloy steels P11/P22 will be followed soon but is it reasonable? What significant importance do you guys see or know about PMI application other than verifying that welders use the correct filler/electrode during welding?

Appreciate to see your answers soon...cheers!

Regards,
Delikado

Expecting life to be fair on you because you're a good person, is like expecting an angry bull not to charge on you because you're a vegetarian.

 

[Dhurjati Sen]

You may refer to API RECOMMENDED PRACTICE 578.

The engineering company's stance is not quite reasonable. The purpose of the PMI on welds (as you have correctly mentioned) is to ensure that the correct electrodes / filler wires have been used. This might look wasteful but with regards to the integrity of the plant, the expenditure is minimal.

 

[EdStainless]

The other reason that you do PMI is to assure that the correct grade of pipe was installed.
I would take 'alloy steel' to mean anything other than simple Fe-C-Mn grades.
So any requirement of Cr, Ni and/or Mo in the grade would make it an alloy (low alloy) steel.

Of course you have another discussion around the need to verify C contents.....

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

PMI is used as a QC sorting tool for materials. The scope of PMI testing is dependent on either the standard/specification or client's requirements. At the end of the day, the client pays for it so you follow their requirements.

 

[weldstan]

How do the Russian regulations apply to your case? They seem to be based on fluid carried and corrosion characteristics thereof.
Most of the Owner/Operators who require PMI to be performed on such alloy pipe systems would require PMI of all the alloys stated except the LTCS. And when low temp filler metals containing Ni are used they have required PMI on those welds as well.

 

[Delikado]

@Weldstan, currently I am at a Russian construction site. Yes Russian regulations put a lot of emphasis on the NDT requirements with regards to fluid carried and characteristics(several cases), unlike ASME where we you only have Cat D,Normal and Cat M, severe cyclic conditions. Their requirement is very complex that literally they themselves could not follow :-D, for example a lot of lines as per ASME belonged to Normal fluid service(RT/UT scope is 5%) but for Russian regulations it belongs to extremely hazardous substances and therefore(RT/UT scope is 100%), not only that, it should undergo first 100% Visual Test(with Reports), 100% DPT/MT then RT/UT(100%) and PMI(100%) if an alloy steel sans the LTCS. The lines are classified into several guidelines including ASME, whatever the most stringent requirement will be applied.

But nevertheless still there is a discussion with regards to PMI application of alloy, whether low alloy is included or not.

Regards,
Delikado

Expecting life to be fair on you because you're a good person, is like expecting an angry bull not to charge on you because you're a vegetarian.

 

In my neighbourhood, refineries ordering pipe spools will order PMI testing as many as three times on the same material:

1) Raw materials at the fabricator;
2) All materials and welds in the finished spools;
3) Spot checks on spools after installation, plus any field welds.

This expense is incurred because the Owner cannot place much trust in the integrity of the international supply chain. Incorrect materials occur frequently enough to justify the added expense - the cost of removing installed material, or worse, having incorrect material fail can be massive (not to mention dangerous).

As a general rule, alloy steels contain >5% total alloy content; steels with <5% total alloy content are low alloy. Once you get to stainless steels they are not so much referred to as alloy steel.

Having said all that, I would want to see PMI done on all materials including carbon steel.

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