Debasis Hardness check of Spheres (used) and in operation - i.e, inspecting to meet SMPV (U) Rule 19 -(mandatory inspection) needs after 60 months of use for a plant handling LPG/Propane / Butane / Ammonia/VCM etc Oil and Major Petro-chemical, Fertilizer companies. Explosive Department, Inspectiom Companies and Minsitry participated and discussed on this in detail to arrive at the parameters and testing methods for inspection under Rule 19 for vessels in operation. and new vessels also. Hardness check is normally done of welds that have been PWHT during construction time. Yet , inspite of S.R of welds and HAZ, Indian users have experienced problems in some plants i.e., both sub -surface and surface cracks. Surface cracks is traceable to fine SCC developed at the inside surface and this is mostly traced to the corrosive contaminant (moist H2S or moist ammonia with oil and mercaptans from refinery or fertilizer plant users) and the relative stress at local spots. Sub-surfce cracks have been observed in some plants. This had clearly given the proof that original S.R done had been inadequate. Still welds with high hardness have been left out in the welds and HAZ . Hardness test is the only simple test method to give you quantitative and qualitative information on this. That is why this had been included in the 5 year testing methods to be done. Mandatory hardness check even at tandom properly done - once in 60 months for statutory inspection under Rule 19 - does not rule out chances of miss during initial plant commissioning S.R resruls and possible high or local hard zones inspite of good over -all S.R of the sphere./ bullet as the case may be. Hardness record once in 5 years confirmed by random check that hardness levels in the equipment are at the same levels or could also throw information on any miss left out earlier to take action. This forum is too short to explain your question on foreign countries. and their experience in steels used for construction for LPG/ Ammonia/ VCM etc . Japanese experience in trying HT 100 is an eye opener in 1960's to the world or Briitsh Steel HSLA steel usage for LPG usage to save vssel tonnage in construction and the spate of failures in LPG vessels - world over - is too well known to all LPG users in Oil & Petro chemical industries. A lot of research and practical analysis was done in Japan and UK based on these problems world over to avoid repetition of the earlier mistakes with likely high hard zones in spite of S.R of the spheres. With contaminants present other than H2S or low concentration of ammonia (oil, moisture, mercaptans etc) in LPG or ammonia storage spheres, residual stress in welds + possible mis-match construction stresses,load stress (hoop stress essentially) can act as nuclei for developing both surface fissures or sub-surface cracks in welds and HAZ of parent material. It is with this purpose that hardness is specfied under Rule 19 of SMPV(U) Rules 1981 to monitor (if not done earlier), missing local stress area points likely to give problems. Hardness test will give qualitative indication /re-conifnrmation of the conditions of welds if tested properly at random . This will also give a basic record for future diagnosis of problems. Users and statutory authorities and inpsection companies have recognized this and this Rule 19 had come into effect in India after well thought out discussion and practical guidelines. Trust this is off help to you C.V.Srinivasan Nishi Engineers Pvt Ltd Chennai July 22, 2005 E-mail:nishi@vsnl.com >In Indian context under control of Oil India Safety >Directorate , Controller of Explosive Department has a >prescription to check Sphere inside weld and HAZ hardness >verification each time when sphere is due for inspection. >As an user we are unable to understand how a material's >initial hardness can vary under chemical storage conditions? >and what is the merit in assessing for such hardness >inspection? Anyone from this forum please respond and share >their individual countries practice in this specific regard.

MJCronin Tk u for the information on this article for refrigerated atmospheric ammonia tank. Debasis Mitra 's question is about pressurized storage spheres in use for LPG/Propane/ Butane in Refinery and Petro chemical plants. and also about pressurized ammonia or VCM / Chlorine spheres / bullets. For your information : Indian regulation has been well framed for the testing and certification. Hardness is one specified in Rule 19 as a simple test method (for N.D.T evaluation of the welds / HAZ). C.V.Srinivasan Nishi Engineers pvt Ltd Chennai India July 26 E-mail: nishi@vsnl.com >Mitra, > >There is a discussion by the European Fertilizer >Manufacturer's Association of hardness inspection of welds >in Refrigerated Ammonia tanks at this website: > >http://www.efma.org/publications/Ammonia%20tank%20inspection/Section%203.asp