If you are looking at discrete parts, pipe, valves, fittings then you are dealing with "MO" cert holders.
IF these parts have been put together into assemblies then these are "NPT" holders.

As a mill just making pipe and tube we had an 'MO' and we sold to specialty distributors or to fabricators (with 'N' stamps).

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P.E. Metallurgy, consulting work welcomed

awesome!!thank you so much for the response
So if you guys as a MO got material for an organization that doesn’t have a MO then is that unqualified source material and you guys would audit their quality program?

More of less, yes. There are some raw material exceptions where the MO isn't needed on the RM but usually that is how it works.
We gave up our MO, too expensive and not enough work.
But of course, we didn't change our QA system.
We continued doing work for a few companies under their certifications as an approved subcontractor.
They would check RM and final NDT (witness), but that was about it.

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P.E. Metallurgy, consulting work welcomed

Thanks so much

I’m assuming you live in the USA. Where does National Board come into play with the nuclear industry?Is it an inspector representing national board visits certificate holder location after the component is completed and he/she determines if the component is up to ASME standards and if so gives a National Board stamp? Do you need a national board stamp or can you just make the competent and apply your asme stamp.

I worked mostly in oil and gas so I’m familiar with API 510 inspectors looking after pressure vessels

I know national board looks after boilers and any pressure vessel not in petro industry. But I’m not sure how/when it applies

I’m learning lots from you in this forum. More than at work!

With an MO the only people that we interact with are ASME and our customers.
WE are not fabricating.
Even heavily processed tube (welded, cold drawn, lots of NDT) is still just material.

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P.E. Metallurgy, consulting work welcomed

Ok thanks. N Holders would be fabricating