According API 650, Table 7.1a, Minimum Preheat Temperature (MPT), if 32mm < Thickness <= 40mm; then MPT is 10°C for Material Groups I, II, III & IIIA and MPT is 40°C for Material Groups IV, IVA, V & VI.
Paragreph 7.2.1.3 shall be take count.
Material Groups are indicated in Table 4-4a.