Hi there Peter,
Is the piping you require actually going to be used to pipe fluid? If not, I have used, in the past, I have used net curtain wire (the stuff you hang the nets up with) If you cut your length of wire and gently warm that over an open flame it corrugates it more. If that isnt the correct diameter what I would so next was wrap string around the outside of the curtain wire and then covered that with electricians' heat shrink and that gives a good effect. If it would help I can post a diagram
and before our DickyD says anything - we have glass in our windows up North with no iron bars across them ::) ::)
just re-read your opening post Peter, and Im having a bad day - have you thought of what they use on the automatic outlet pipes for automatic washing machines and that sort of product. aye its this cold getting to me!!!
aye
John E
BLUEBIRD