These double envelopes are to be considered as part of piping if the function of these double envelopes cannot be disassociated from the internal piping intended for the transport of the fluids.
Reason:
The technical rules for the design and the manufacture of these double envelopes are usually the same as those for piping.
Note 1:
The double envelopes of piping covered by this guideline are of two types:
- those intended to insulate products transported by the internal piping by circulation of a fluid (vapour, coolant, glycol water, etc);
- or those intended to ensure the containment of the product transported in the event of loss of tightness of the internal piping (double envelope for the transport of very toxic fluids for example).
Note 2:
This guideline does not address heat exchangers (see PED Guideline B-04), or reactor loops.