Krish Answer to this complicated design, material failrue problem is not easy to give on a discussion forum. Your problem needs a diagnostic analysis - from process and mechanical design of support for heater coils, failure history, material usage, laboratory analysis on nature of failure. on failed support brackets Suggest engage an experienced consultant - well versed in metalurgy, corrosion, design aspects - if in-house capabiity is limited for the same. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India Nov 11,2005 E-mail: nishi@vsnl.com >Dear members, > > We had frequent failure in the Visbreaker Heater top tube >support plate. The furnace details are as follows, > >TYPE: Box type furnace with vertical coil arrangement with >convection. > >No.of PASS: 04 > >Design tube metal temperature : 560-620 Deg.C > >Tube size : 101 mm OD x 8.0 MM AWT > >Tube Material : A335 GR.P9 > >Tube length : 10.9 mtrs. > >Fuel fired : Furnace Oil with 2-2.5 % sulphur > >SUPPORT ARRANGEMENT:- > >TOP ANCHOR SUPPORT. > >CAST PLATE IS DIRECTLY WELDED OVER THE PAD IN THE TOP RETURN >BEND.(RIGID) > >BOTTOM SUPPORT: SPIGOT ARRAGEMENT (FREE MOVEMENT) > >TOP RETURN BED SUPPORT CAST PLATE IS 30 MM THICK AND 800 MM >LONG OF 50 Cr- 50 Ni material.(Secured with bolting >arrangment at heater outside in the beam) > >Failure: Top anchor support cast plate is frequently failing >(breaking in to two halves) while heater in service. No >abnormality in heater operation. Temperatures are within the >design limit. We found casting defects in rest of the >plate/failed samples and mostly of gas >pockets,shrinkage,sand inclusion in cluster. > >My question apart from casting defect any other reason for >such failure. > >1)Is it sound practise to design visbreaker heater coil in >vertical type rather than horizontal due to high operating >temperature. > >2)Is it a good design of providing top rigid anchor support >in vertical coil arrangment in visbreaker heater? > >3)What is the expected vertical differencial thermal >expansion in such type of support. Tube material is P9 and >support material is 50 Cr-50 Ni. > >4)Can we replace the top rigid support with wall hanger cast >support for free movement of tube vertically? > >5)What about providing spring support in lieu of rigid >anchor plate type support? > >Your comments are highly appreciated. > >With regards, >krish