Nigel Calder recommends copper pipe in his new Cruising Handbook. He does
comment that you need to use flare-type connections and not compression
fittings.

Copper is completely unacceptable for use with acetylene as it forms
explosive copper acetylide deposits in the pipe. Use only hose for your
welding rig g

doug dotson wrote:

I don;t think copper for propane is acceptable for boats in the US. The
surveyor
made me remove all of it on my boat when we bought it. The
boat came from Canada where I guess it must be OK. He also made me
replace all the copper fuel line as well.

Doug
s/v Callista