Kishan High hardness > HRc 22 (> 240 BHN) in sour environment affects materials . Going through NACE MR 0175 and API - RP suggested guidelines will help you to understand better. NACE had further lowered this to HRc 20 (< 220 BNN) in recent years. Please refer NACE MR- 0175 latest edition. To explain in simple way, for SCC to occur, tensile stress and a corrodent is needed. Higher the stress, the lower the corrodent cocnentration s needed to attack for any of the possible mechanisms for cracking to occur . Temperature and aeration / agitation plays additional effects or in other words accelerates the effect for the same T.S and lower concentration of corrodent to affect the material. For SCC, a minimum threshold stress is always needed. If the tensile stresses are lower than the minimum threshold limit then chances of SCC,HIC, SSC etc would be limited or delayed further. NACE/ API RP guidelines had evolved the limit of HRc 20 after discussions and opinion and practising experience of failures in different materials in different environments including sour services. Trust this helps you C.V.Srinivasan Nishi Engineers Pvt Ltd India March 22,2007 E-mail: nishi@vsnl.com >How hardness effects the steel when used in sour >environment, for HIC, SSC, SZC and etc... >More than 22 HRB steel is not prefered for sour service. >Why?