Krish Your LPG Bullets are 35 years old with nil C.A (Corrosion Allowance). 5 year SMPV(U) Rules 1981 statutory certification if it had been done properly by the inspection company (whom you entrusted the job) and if the inspection company had properly estimated the depth, number of pitted areas and locations in the vessel (by thorough pit mapping of the profiles of pitting seen) , you may have to give discounting factor for the remaining thickness in shell plates for the pitting seen in the vessel. Your question did not give this detail on the extent of pitting estimated / evaluated by the inspection company. Taking the pitting factor into account, you may have to re-work out the revised design value and probably revised set pressure for SRV. For this, based on the pitting estimated, the inspection company should have suggested this revised design pressure and revised set pressure for SRV. If that is not done yet, you may have to do that again and apply to CCE Nagpur for this revised design rated value. Frequency of inspection periodicity will be decided by CCE Nagpur depending on this revised value and the amount of pitting reported in the last 2 inspection done for each Bullet. A 201 FBQ - original 16 mm thickness- may stil have service life at probably lower rated design conditions than the original rated design conditions - since you may not have evaluated the extent of pitting, pitting depth, pitting area, pitted locations. If you follow the above approach you can operate the 35 year vessel safely at lower design conditions. Pitting due to wet H2S will continue. Frequecy for inspection will have to be decided based on the calculation done and revised values. We have inspected >35 year old ammonia spheres for some plants. Your situation is near parallel. If care in testing to the ASTM specification and standards had been done for N.D.T inspection by the inspection company, to critically assess a 35 year old vessel with Nil C.A, ( for the certification responsibility vested) using an old vessel may not pose any limitation. Trust this answers your querry. C.V.Srinivasan Nishi Engineers Pvt Ltd India Sept 08, 2006 E-mail: nishi@vsnl.com >We have quite no of LPG bullets commissioned in 1970-72.The >shell material is A201 FBQ(Fire box qaulity plate) without >any corrosion allowance.The plate thickness is 16.0 mm only >and the design pressure is 13kg/sq.cm. > >Sofar,no major failure were experienced in these bullets >except internal pitting due to presence of H2S. These >bullets are being regularly inspected as per SMPV rules once >in 5 years. > >Is is advisable to put these bullets in service since it is >35 years old?Is there any problem expected due to wet >H2S/Caustic attck since the original plate is not as clean >to resist SSC/HIC etc. > >Is there similar type of bullets are in service anywhere? > >Kindly share your experience in this regard.

Thanks to Mr.C.V.Srinivasan & MC for their valuable comments.The max depth of pitting noticed is 2-3 mm scattered all around at the bottom mid section only.Remaining portion are having max of 1.0 mm deep pitting.As Mr.Srinivasan pointed out the opearting pressure of these LPG bullets are around 9.0 kg.sq.cm only against the design pressure of 13.0 kg/sq/cm. regards,