Luis Presence and entry of 1000 ppm H2S in Propane is very high. How you did not experience this cracking in so many years of operations? In my view, you should have observed this cracking trend at the first time you inspected - i.e., after the first entry of this high level of H2S in the sphere. Or is it a recent 2-3 years problem of high H2S content in propane and you have inspected the vessel for the first time after this H2S content entry? BH 36 with the hardness level - in parent and HAZ (after PWHT) should not be affected for normal H2S permitted in Propane (5 ppm only). 1000 ppm will affect the steel. If it is only surface cracks, inspite of your repeated repair welding and re-PWHT operations, you can leave minor cracks and still operate the vessel and still monitor the cracks from out side during operation even with minor SCC cracks left over. You can do: Localized compressed grit blasting of the welds will improve and surface cracks will not propagate deeply inside (this will introduce compressive stresses locally at the inside surfaces where minor cracks are still present). Also if H2S in Propane is likely to be 1000 ppm again, you will have more serious problems in the near future. If it is sub-surface cracks, you have to remove and keep trying till all cracks are removed. For future, sphere has to be inspected from inside once in 2 years by MPT/TOFD to ensure that cracks had not propagated deep - if you have to re-start plant with minor surface fissures and monitored from external surface and establish if the minor cracks had not propagated deep. Hope this helps you. C.V.Srinivasan Nishi Engineers Pvt Ltd India March 27, 2008 E-mail: nishi@vsnl.com >Hi CVSRINIVASAN > >Thank you for your usual great sharing. To complete my >previous posting I say the following. > >The sphere has about 30 years and the material is BH 36. > >BH 36 is a fine grain steel with weight of C, 0.01 to 0.2% >by weight of Si, 0.2 to 1.5% by weight of Mn, 0.01 to 0.07% >by weight of P, 0.006 to 0.015% by weight of S, 0.01 to >0.08% by weight of sol. Al, not higher than 0.004% by weight >of N (N < where 0.002. > >On repaired zones we found on weld deposit hardnesses >between 200HV and 220HV and on base metal values within >145HV to 175HV > >During operation of the sphere it was detected >contaminations of H2S in the propane of about 1000 P.P.M. > >The sphere was totally PWHT even the zones not involved in >repairing operations. > >Best Regards > >Luis marques