An elaborate array of Nickel piping is used in the cooling of TiO2 ( Titanium Dioxide) compound directly from the reaction chamber. As it enters the piping system, it is under very high temperature and velocity. Additions of salt are also introduced to aid in a scrubbing action. The environment is extremely corrosive and abrasive, resulting in high maintenance of sweeps and elbows within the piping system. A complete erosion of wall thickness has been known to occur in less than nine months. Reconditioning the sweeps with weld metals of similar chemistry of the piping prevents discarding the expensive component but does little to extend its overall life. However, extensive and significant component life can realized by the application of proper hardfacing materials and procedures.
Sweeps can be rebuilt successfully by cutting a series of windows in the inner radius thus exposing the inside of the outer radius. A thorough cleaning of the surface is necessary to ensure proper bonding of the weld metal. The worn area can be rebuilt to size with welding products whose properties closely match the base material. Once this is complete, the proper application of one of three Postalloy Nickel Base products will guarantee maximum component life. A recent application of one layer of Postalloy 2813-MCG to a major pigment manufacturer’s sweep resulted in essentially no wear after nine months. According to the Maintenance Manager, “The weld spatter was still present after 9 months of service”. The Maintenance Manager is now considering applications in other highly wear prone areas.
The choice of Postalloy Nickel Base products should be selected upon the level of hardness and corrosion resistance desired. The higher the hardness, the more hard particles present in the deposit and the higher the abrasion resistance and the lower the corrosion resistance. It is suggested that Postalloy 2813-MCG act as the initial selection because of its intermediate hardness and corrosion resistance. A shift to either higher or lower hardness can be made after preliminary inspection.
Postalloy 2812-MCG Machinable deposits. High corrosion resistance. Least abrasion resistant. Hardness 35 to 40Rc.
Postalloy 2813-MCG Deposits finished by grinding. Intermediate corrosion and abrasion resistance, Hardness 45 to 50 Rc.
Postalloy 2814- MCG Deposits finished by grinding. Highest abrasion resistance, least corrosion resistance. Hardness 55 to 60 Rc.
Cut appropriate number of windows on sweep inside radius to expose inside of outer radius.
Clean dirt, grease and debris from all surfaces to be welded. Grind if necessary. Choose appropriate wire type and diameter compatible with the job requirements and available equipment. Select Argon/Oxygen mixture at 35CFH. Preheat and Interpass Temperature: 200 to 250F.
Deposit single layer with weave pattern working in a vertical up position.
Some check cracking may occur, which is usually not detrimental to weld integrity or to the performance of the deposit.
Complete all repairs.
Slow cool to room temperature.
Finish machine or grind if required.
Replace windows and place in service.