might be one alternative

I think, an explanation is not required

From the little context that we have there could be several interpretations, and each one of the given suggestions can be defended. However, you cannot rule out the possibility of "authorised to procure / purchase" in the sense that this guy is perhaps heading the purchase / procurement functions. You are in a better position to assess from what your sentence follows / precedes.

It is not that you purchase pressure vessels or piping system often, but this guy could be the one who decides on the pressure vessels / piping system and related components

German term (edited): Abnahmetätigkeit als Befähigte Person für

...is how I read it.

"inspector" means a person recognized by any province or territory, according to the provincial or territorial laws, or by the National Board of Boiler and Pressure Vessel Inspectors, as qualified to inspect pressure vessels and pressure piping
http://tinyurl.com/2f45zkl.

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Note added at 24 mins (2010-11-03 16:46:16 GMT)
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Code Qualified Inspector An inspector who, by training, experience, and passing the National Board Boiler Inspector Commission Examination, is qualified to inspect pressure vessels, systems, and relief valves.
https://sbms.bnl.gov/sbmsearch/subjarea/171/SAdef.cfm?id=171

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Note added at 12 hrs (2010-11-04 04:26:03 GMT)
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Alternatively, as in the second ref above,
Qualified Inspector

...as competent person ...

I think "acceptance activities" would be okay, too, but inspection means all the actions necessary for the final acceptance.

Befähigte Person = competent person (see for example link below - VDI should know:)

I know those expressions because since I am working in a quality assurance department I am involved in these processes on a daily basis.