Weld repair of Casting

By rajaramc Date 05-29-2005 08:38

A cast strainer of ASTM A 217 C5 of Dia 24" and wall thickness of 30mmm is having multiple branched cracks scattered over an area with length of 200mm and 100 mm width. I have to write a repair procedure for the strainer. I am hoping for some inputs from our experts in this forum
Background :
The strainer was exposed to a fire situation in a oil refinery. To salvage the strainer, it was shot blasted and MPI checked. No relevant indications were observed. High hardness values of 280-300 BHN were observed at different locations on the strainer body. The strainer was then stress relieved at 730 Deg C for 3 hours. After stress relieving, the hardness values were below 241BHN . Post stress relieving , MPI examination revealed multiple branched cracks scattered over an area with length of 200mm and 100 mm width. The cracks are visible in Radiography also.

Is it advisable to go for weld repair of the cracks? What would be the best way to go about the repair ?

By MBSims

Date 05-31-2005 03:44

It's kind of tough to recommend a repair without knowing the cause of the cracks. They could be quench cracks from rapid cooling after the fire (water?). Rather than try to chase a lot of small cracks, it would probably be easier to cut out the area and weld in a piece of 5Cr plate rolled to the radius of the strainer. You should examine the weld preparation with liquid penetrant or magnetic particle examination after it is cut and beveled to ensure no cracks remain. If both sides of the weld are accessible, a double-vee groove should be used to minimize the welding, with root backouged to sound metal prior to welding the opposite side. A 400 F minimum preheat should be applied during welding and a 1300-1400 F posweld heat treatment will be needed. I believe the matching 5Cr electrode is E8015-B6 or E8018-B6. Perform MPI and hardness testing again after PWHT is complete.

By rajaramc Date 05-31-2005 07:14

Thank you very much for your input. The weld will be accessible from only one side. I am also considering the use of E NiCrFe-3 electrodes in place of E-8018B6 .

C.Rajaram

By GRoberts (***)

Date 05-31-2005 19:05

Before cutting out a 200mm x 100mm area, I would excavate some of the cracks to see how deep they go. If they are not that deep, I think it would be easier to gouge or grind the surface until it is free of cracks, then repair with 8018-B6, and perform a stress relief. Do you think the part got above the lower transformation temperature during the fire to result in the hard areas? If so, the properties of the casting may be in doubt because the cooling rate could be just about anything. You have to get a good heat treatment in order to get the 90ksi minimum tensile strength specified for A217 C5 material. You can use 400F preheat minimum, but we have found 500F works better (fewer cracks).

By rajaramc Date 06-01-2005 12:54

The strainer was definitely quenched by the fire fighting operations. This could be the reason for the high hardness values. Unfortunately , the health assessment of this particular equipment could not be done as it was dumped along with the scrap. I am getting a metallographic replica survey done at few locations to get an idea of the microstructure near the area of cracking.
Due to urgent requirement of the strainer for start up of the fire damaged unit, it has been decided to repair the cracks by gouging out the existing cracks. I hope to use a higher preheat of 500 deg F and hopefully will see lesser cracks.