I just want to discuss about something...my firm always doing drum shells (for boliers) of 15NiCuMoNb5 (WB36) material, and there's almost every time same problem - cold cra-c-k-ings after finally pwht. we finally find some solution...when there's a late hold cra-c-k-ings (48 hrs. after pwht - NDT testing shows)...:
1 - all imperfections must be removed with grinding
2 - the circles around the imperfections must be preheated at temperatures >150°C, in diameter of minimum 500 mm around the removed imperfections
3 - repairs must be done in horisontal welding position (PC) - off course, the drum shall be rotated to make possible to the welder to weld in PC position
4 - using of DMO-Kb electrode, welding without of waving electrodes, just straight pulling, in few passes
5 - the last electrode pass must be slowly and carefully grinded
6 - then comes more heating, without interruption of already preheated tempetature of > 150°C; the heating speed shouldn't be over 40°C per 1 hour, and then when it reach 280-300°C that temperature must be keeped for 2 hrs and then comes slowing down to the room temperature, again cooling speed must be slowed, not so slow as heeting rate, but..50-60°C per hour is maximum
7 - then comes NDT; only with dry magnetic particles (dry fluxes are more then wishfull), and NDT must be performed on whole drum shell, not just places where the imperfections was
8 - pwht comes; 580-600°C, depends on drum thickenss; mostly it's 2 hrs.
9- 48 hrs. after finishing pwht - again comes magnetical particle NDT with dry things, without hydrogen content
so...does anyone have experince with this WB 36 drums? and how do you solved the cold crac-king problems?
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