Inspector 1978 For a new vessel to be commissioned, Hydro test @ design x 1.5 taking temp-pressure correction factors for the material and liquid or fuel stored service application is to be done to meet ASME Sec VIII Div 1/2. This takes care of both load factor at column legs or supports when vessel is hydro tested at normal ambient temperature conditions. Pneumatic deviation @ 1.1 times is mostly not applicable for a new vessel to be commissioned under ASME Sec VIII Div 1/2 as pneumatic test does not take into account the full load factor for the support leg columns and for foundation stability. ASME Sec VIII Div 1/2 recommends pneumatic test normally upto 100 PSIG ( 7 KSC). Pneumatic test beyond 100 PSIG ( 7 KSC) can be done as per ASME Sec VIII Div 1/2 in special cases @ 1.1 times with special and extra care of check beyond static fill of vessel upto hydro static head for the liquid or applicable service taking the factor of sp.gr of the fuel or liquid used. For an used or already existing service vessel, which has to be mandatorily tested as per applicable statutory rules of Country's governing laws and rules under specific explosive or factories rules, pneumatic test @ 1.1 design pressure (again taking into account temp-pressure correction factor for the service applicability of liquid or fuel stored in the vessel) or test with hydro test @ 1.5 times the operating pressure conditions instead of design pressure @1.5 times. If it is boiler, it will have to undergo testing as per IBR rules. If it is explosive materials storage, it will have to undergo tests as per existing Indian or different country's as applicable. Visual examination for a large vessel - sphere or bullet - may not be able to distinguish in small distortions in diametral expansions. Perimeter expansion at the maximum diameter or at known circumferences is one method used for knowing the quantum of diametral expansion (indirectly measuring -out of roundness at the maximum diameter by circumferential physical tape measurements) during hydro test time. Other way is to fix known strain gauges at suspected areas where maximum stress intensity is likely in the vessel and compare the same readings from loading to un-loading the vessel during water fill and during water drainage to know the exact quantum of strain seen during hydro test. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India Jan 09, 2010 E-mail: nishi@vsnl.com >Dear Experts > This is not a corrosion issue.But i definitely >think i will a get a reply for this question from this >forum. > > Generally we are doing hydrotest of newly >fabricated vessel as per Sec V111 div1 &2 at 1.5 time of >MAWP.Some time we are deviating and saying pneumatic test >can be done at 1.1 of MAWP.Code also allow the same. > > My question is the integrity that could we >assure after the hydrotest and pneumatic test is the >same?Because in hydro we are applying 1.5 times and in >pneumatic we are applying 1.1 times? > > Also sec V111 says if we exceed hydrotest >preesure it can be accept the test if there is no permanent >distortion by visual examination?How we can check the same? > > Also how to measure the out of roundness of >vessel.any special method available? > > > >Regards

One should be grateful to Mr. Srinivasana for his continued interest and education imparted in this forum. To mention Hydrotest is a strength test whereas Pneumatic test considered to be as Leak test.