Debasis You are fully aware : H.T. of Spheres / Bullets - using Explosive chemicals - come under SMPV(U) Rules 1981- Indian Explosive Act - GOI. N.D.T Inspection to meet to SMPV(U) Rules 1981, for vessels coming under Indian Explosive Act, GOI, is clearly ruled out for the user and inspection company to follow and test before commencing H.T. Prior N.D.T inspection before HT forms a part of 5 year Statutory inspection and certification. H.T has to be done in stages of filling at known rates of filling, waiting for sufficient time during each stage of loading, final H.T at rated H.T test pressure, gradual removal of water after H.T till empty condition. In the case of LPG/Propane/Butane etc Spheres, used in Refinery / Petro Chemical complexes, water filling has to be done - First time complete water fill to ensure LPG vapor load is vented out through flare stack before checking for oxygen levels for human entry for work and inspection inside the sphere. Even here a gradual stage of loading (filling at known rates of filling, waiting for time for settlement) and again gradual removal of water has to be done. The same has to be repeated for final Hydro test after post N.D.T Inspection and repairs if any (called for). BS 5500 is the most correct and specific code which details ways of loading and un-loading a pressure vessel for H.T. ASME Sec VIII / IS codes do not specify very clearly the details of H.T for a pressure vessel. This means LPG/Propane type Spheres are subjected to twice full H.T fill loading within a span of 30-40 days time. Columns / Leg suports are no doubt designed for this - after a thorough soil survey, fuondation detailed study for the sphere. Some Indian plant users have experienced major problmes during loading and un-loading for H.T (i.e., fundation leg support giving way suddenly to call for major re-design, repair jobs later). Columns and leg support and leg support to shell at equatorial axis level is mandatory to inspect as per SMPV(U) Rules 1981 using WFMPT or if possible to carry out UT Flaw check also. An experienced and accredited inspection engineering and certifying company (if entrusted to do the job) will guide the plant the procedures and methods to employ for final and pre- H.T for LPG spheres. If soil settlement is expected by the plant, some user plants also specify and also carry out leg settlement record ( in addition to conventional water level monitoring) strain gauge method as well theodolite measurements of leg settlement records (both during water filling, waiting time for settlement, hydro test time, and during un-loading of water till empty). Strain gauging is more correct for leg settlement. It is costly. This requires reliable way of recording data for correct interpreation of results. Accuracy of fixing strain gauges and record is also needed. Comparatively, Theodolite and conventional "U" tube manometer water level measurement records also give reliable information if e proper care and record keeping is done by the plant user and the inspection company engaged for the work for certifying the sphere. For your information, representatives of Explosives Department, Government of India, User plants (Fertilizer, Chemical, Petro Chemical, Refinery users),accredited Third Party Inspection companies had jointly discussed threadbare all implicaions and practical problems in 1993/1994. The amended SMPV(U) Rules 1981 - 1994 clearly specify the testing requirements for LPG or Ammonia Spheres for both used and new spheres or bullets etc. Trust this answers your querry. C.V.Srinivasan Nishi Engineers Pvt Ltd India September 7, 2006 E-mail: nishi@vsnl.com >Dear Readers, > >Hydrotest of Horton Spheres are normally done Post Dry >Inspection of Horton Sprehes Insides . The water is filled - >Hold in stages and hydrotest is done as per norms. > >For Old and aged sphres ( even for newly commisioned >spehres) it should be a standard Practice to ensure the >safety and integrity of Support Legs and foundation before >Peak HydroTest . One documents claims comment of one >Internatinally accredited Class I Inspection Agency under >LPG Sphere perspective that Foundations & Legs are >overdesigned to about 8 times the weight of LPG and 4 times >that of Water. > >A discussion / opinion of NDT Inspection >strategy/requirement of Legs ( without removing Fireproofing >) and foundation is requested for. > >regards > >DM

If you are doing first time inspection after commissioning it is better to strip out the entire concrete and see the condition. Many leg failure have been reported in worlwide due to corrosion under concrete due to ingress of rain water/fire water from sprinkler during testing.As suggesed by RTD, we can carry out corrosion mapping without remove concrete however the sensitivity of decting pitting & stress cracks at tie-in bar location is highly questionable. regards, krish