Inspector 1978 Forged Flange SS 304 L shows a extremely large coarse grain ( ASTM Zero grain size shows extremely large grains) . This may not be possible for a forged product in SS 304 L Nozzle to forged flange HAZ shows fine grain (ASTM 5to 6 grain size) in SS 304 L from welding effect From description it is not clear if crack had originated at the nozzle to flange HAZ of weld. It is not possible to have a crack for such large grain size forging. Manufacturing defect due to forging in such large grained structure may be ruled out for now and it is not also possible to achieve such large coarse grain in forged components in SS 304 L. Second if it is forged component for flange one could expect some twin grains and not uniform Zero grain (very coarse grain structure) or Size 0 to 1 equally very coarse grain size. Such a large coarse grain structure may not be possible for a properly forged and heat treated flange. It is quite possible that the flange supplier had solution-annealed normal plate material instead of forging to get such a large coarse grain structure in SS 304 L forged flange. From description it looks that it could be fine SCC which normal RT/ phased array cannot detect with tight SCC in SS 304 L. Simple DP test on nozzle to flange weld had given definite indications of this trend. SCC cause could be either chloride induced or caustic induced from BFW. For this temp seen in shell and tube side, it is highly unlikely to have Chloride SCC. It is quite possible that caustic SCC at low temp could have contributed to the leak noted at the nozzle to flange joint HAZ. In-situ metallography should have revealed fine Intergranular SCC at the nozzle to flange joint HAZ? Please recheck at the insitu metallography pictures or re do the same on the sample available. There is also a possibility of caustic concentration from BFW at the HAZ affecting over a period of time. You could do micro hardness test along with in-situ metallography replica to know the hardness at the fine grain area of nozzle to flange joint. If micro hardness indicate high residual hardness then this indicates caustic concentration effect due to BFW. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India June 29, 2010 E-mail: nishi@vsnl.com >Dear Experts > >We had a typical failure in our hydrogen plant in Boiler >Feed Water heater (stacked exchanger) in nozzle to flange >joint near the HAZ. > >Service : Shell side - BFW(Bolier feed water) > Tube side - Process gas(70 % Hydrogen,20 % >CO,3 % C02) > >Design Temp : Shell side 51 deg C Tube Side - 28 >deg C >Operating Temp:Shell side 46.9deg C Tube side - 24.6 deg >C > >MOC : Channels SS 304 L > Flange SS 304 L > Tube SS 316 L > >We have done an Insitu Metallography of the weld joint.We >are getting zero grain size in the crack location and 5-6 >grain size in good locations. > >We have also done several NDT'S like RT,Phased array ,wet >fluorescent DP of cracked location All showed indications >but a noraml person who don't knw there was a leak cannot >differentiate the indication. > >We are suspecting manufacturing stage problem could have >created the problem.Exchanger is in service for 1.5 years. > >I would like to know the experts view on the same.How could >have forging problem can develop into this type of >crack.What is grain size?what is zero grain size how it >develops in forging? > >Please put some light in this matter > >Regards

Inspector 1978 Inter granular cracks at HAZ/parent material indicate SCC as the cause (whether chloride or caustic). Twin grains seen in parent shows the material had been forged and probably solution annealed to get this coarse grain size ( close to ASTM Zero size) Still you could get /do micro hardness on the fine grained and coarse grained areas (ferrite and austenite grain areas) to know if any high residual stress (either due to weld geometry or from high heat input and cooling effect from welding) had played a part at this low service temp of operation of BFW. If micro hardness is more that would confirm the mode of cracking for BFW at service temp of 50 deg cent to develop this cracking (SCC) SCC is difficult to detect with Fluorescent DP also unless it had developed into multi branching cracking. Problem experienced in another exchanger is likely to be similar to first failure from description given. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India June 29,2010 E-mail: nishi@vsnl.com >Dear Mr Srinivasan, > >Thank you very much for your reply.Yes i found it very >informative and useful. > >I fail to mention in the above post we have observed >intergranular cracks in the HAZ and in the parent material. > >Following is the report provided by the laboratry " >microstructure at weld shows ferrite pool in austentite >matrix wheras HAZ shows coarse grained austenite structure >with twins. >Microstructure ate parent material shows coarse grained work >austentic structure with twins.Presence of heavy >inter-granular crack is observed in HAZ & PM region ASTM >Grain size -0. > >We have don Wet Flourscent DP of the joint .But it also >fails to reveal the indication. > >We are having one more leakage in another train of same type >exchanger.They also haveing same heat number embossed on it >as flaged flange. > >Please help us how we can proceed with the same. > >Also you have mentioned in your reply :"It is quite possible >that the flange supplier had solution-annealed normal plate >material instead of forging to get such a large coarse grain >structure in SS 304 L forged flange. " > >Sir can youn please explain this in little more detail. > >Regards