Well without going on a further specific masters course in pipeline engineering you need to start working from some sort of design/ consulting company who specialise in this field or operating company.

That's quite a large field so you probably need to narrow it down a bit to a particular area/ city or field of business.

Piping and pipeline are distinct things with different design parameters and issues.

Basically get lucky one day.

I have a Mech Eng degree and didn't know a pipeline even if I fell on it before I got my first job working for a pipeline operating and engineering company and just went from there. Pure luck. And my magnetic charm of course....

Would it happen again today? I think those with the further qualifications may be in front of you, but try finding a person to advise you at one of the bigger oil companies / utility companies and ask around - do a bit of searching on line, find an industry organisation that sort of thing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Any natural gas utility typically has pipeline engineers. Check with whatever local utilities are in your area and see if they have entry level stuff. Otherwise look at consultants as LI said or look at the big players like TransCanada, etc.