Many thanks to all who responded to my query regarding standards for the above. The nearest I got to an ISO standard was BS 5500 which is apparently equivalent to ISO 2694.
On the same subject there is now published a pressure equipment directive 97/23/EC which I am advised will enter into force on 29th November 1999 with a transition period until 29th May 2002. Which is worth bearing in mind if anyone is designing new products this also includes vacuum vessels operating at pressures below 0.5 bar. Once again many thanks Brian Harlowe * opinions expressed here are personal and in no way reflect the position of VG Scientific
