NBN EN ISO 13704:2008

ISO 13704:2007 specifies the requirements and gives recommendations for the procedures and design criteria used for calculating the required wall thickness of new tubes and associated component fittings for petroleum-refinery heaters. These procedures are appropriate for designing tubes for service in both corrosive and non-corrosive applications. These procedures have been developed specifically for the design of refinery and related process-fired heater tubes (direct-fired, heat-absorbing tubes within enclosures).
ISO 13704:2007 does not give recommendations for tube retirement thickness; Annex A describes a technique for estimating the life remaining for a heater tube.
The procedures given in ISO 13704:2007 are not intended to be used for the design of external piping.