Allowable stresses
37. The permissible general membrane stress for predominantly static loads and for temperatures outside the range in which creep is significant must not exceed the smaller of the following values, according to the material used—
(a)in the case of ferritic steel including normalised (normalised rolled) steel and excluding fine-grained steel and specially heat-treated steel, 2/3 of Re/t and 5/12 of Rm/20,
(b)in the case of austenitic steel—
(i)if its elongation after rupture exceeds 30%, 2/3 of Re/t
(ii)or, alternatively, and if its elongation after rupture exceeds 35%, 5/6 of Re/t and 1/3 of Rm/t,
(c)in the case of non-alloy or low-alloy cast steel, 10/19 of Re/t and 1/3 of Rm/20,
(d)in the case of aluminium, 2/3 of Re/t,
(e)in the case of aluminium alloys excluding precipitation hardening alloys 2/3 of Re/t and 5/12 of Rm/20.