FLOATING TOOF TANK WITH H2S MIXTURE 2

Hydrogen induced cracking (HIC), caused by H2S service, is generally only a concern on pressure vessels. However, current practice by most of the oil majors is to select tank materials which exhibit low hardness levels in the heat affect zone (HAZ) after welding. Generally the hardness levels are restricted to about 200 HBN or 248 HV 10 in the weld metal, HAZ, and parent material. If the intent were to design a new tank, I would recommend the use of a low strength steel such as ASTM A36 for shell, roof, and bottom. A hardness level of 200 HBN should be easily achievable with this material. With regards to design standard, I would recommend that you use API 650, “Welded Steel Tanks for Oil Storage”. On larger tanks where it is not feasible to use low strength steels, the norm is to use HIC tested steels. The chemistry of these steels also needs to be tailored so that the low hardness levels are maintained.