Gentlemen
Does anyone know if there is a Code which deals specifically with the design of large diameter piping (in this case high temperature ducting). By large I mean diameters > 1m. One of our clients tells me there is such a code but I am not familair with it. Any advice would be appreciated.

Thanks in anticipation.

SMACNA covers ducts here in the U.S.A. a duct being in some cases a thin-walled cylinder but its direction will be of little help to you IMHO.

If the governing code of plant is the process piping(ASME B31.3) and duct line is a part of piping system, piping design code will be the ASME B31.3 regardless of pipe size and thickness.
I had experienced FCC/RFCC duct lines(catalyst transfer lines, 60” ~100” with SS 304 steel or C.S refractory lined), EB/SM process lines(styrene , 90”~117” with Alloy 800HT and SS 304H…), and 60” aluminum duct line for Sulphur plant…all the piping design code was the ASME B31.3.

Of course there are some special considerations for the designing of large thin walled pipe(D/t ratio larger than 100) with elevated temperature.

Mr. Wee is correct...

But as for what code is used for "ductwork" SMACNA is used here.

I suppose your first task is to identify which code is applicable.

In either case you will need to take localized loads and their resulting stresses into consideration.