Luis If it is surface crack - MPT will be the most reliable and fast technique. If it is surface combined with sub-surface crack in some HAZ or welds , UT Flaw check will help. Confirmatory RT will do to keeep record of the sub-surfce crack. TOFD : To what extent this will help you - i am not sure. In-situ metallography (Replica at HAZ, Parent plate and un-affected portions of welds and parent metal areas) will give you input on the nature of crack. Replica taken can be viewed in laboratory metllography. I suggest that and you can take micro-hardness on the phases and at the grain boundaries . This would help you to know whether SSC Type ! or Type 2 or HIC is predominant. I do not think it will be SOHIC. It will be in all probability SSC - Sulphide Stress Cracking - Type I or Type II . If you suspect HIC is the predominant cracking mechanism, after micro hardenss on the replica taken - at the HAZ, at the parent metal, and also un-affected portions without crack befoe determining the predominant mode for this surface or sub-surface crack. For HIC or SOHIC hardness should be high. If you had done PWHT then chances of this after 28 years operation are not likely. Please take hardness on the welds / HAZ and parent materials along with MPT and UT Flaw check. C.V.Srinivasan Nishi Engineers Pvt Ltd India Sept 15, 2005 E-mail:nishi@vsnl.com >C.V. Srinivasan >In April/May 2005 our sphere has suffered H2S contamination >during about three weeks. Sphere plate material is P335NL1 >NF-EN 10028.3 with the following composition: C-0.138, >SI-0.48, Mn-1.55, P-0.011, S-0.0004, Al-0.041, Cr-0.032, >Cu-0.016, Mo-0.009, N-0.0058, Nb-0.027, Ni-0.039, Ti-0.002, >and Fe-Bal. >It is a low S plate. The sphere was PWHT. Operation >temperature is 40ºC. Working pressure is 15.5 bar g. > >Inspection done during the construction/erection of the >sphere IN 1978 didn’t reveal relevant defects and all NDT >such as Rx MP and UT done at that time were accepted by the >codes. MP and UT done during last intrusive sphere >inspection in 1999 didn’t reveal defects. > >We strongly think that the cracks now found on HAZ welds >have been induced by H2S contamination > >We didn’t count yet the number of relevant indications >because the inspection is still in progress but at the >moment there is a lot of cracks. We are going to complement >MP testing with TOFD scan and we will perform some >metalographic replicas, after that may be we will be in >conditions to evaluate HIC, SOHIC or SSC like indications. >Meanwhile if in your opinion there is something else, we can >do please let us know. > >Regards > >Luis Marques

Dear friends On sphere top dome, we found on weld edges, about 100 cracks 2 mm deep, by MPI inspection. On top circular weld, we found through TOFD about 90 indications of defects between 11mm and 22mm deep up to 600mm length. TOFD operator says that defects indications are similar to lack of fusion weld indications. By the codes all the above defects should be repaired. Mean wile as per C.V.Srinivasan suggestion to evaluate HIC we are going to do replicas and also micro hardness at the HAZ, at the parent metal, and also in un-affected portions without crack Plate thickness is 40mm Luis Marques