体彩20选5基本走势:Nickel Alloys used in Pulp and Paper industry
Nickel alloys are used in pulp and paper mills generally where conditions are the most corrosive. Alloys 600 and 800 have been utilized for more than 35 years for digester liquor heater tubing because their high nickel content provides excellent resistance to chloride SCC. In the disposal of organic wastes in unevaporated black liquor, alloy 600 has been used for the reactor vessel, transfer lines, and piping.
A major problem in this industry has been the cracking of steel digesters in the weld area. A practical solution to the problem is to weld overlay the weld area with alloy 600 or 625 filler metals. Other methods are the use of alloy 600 or 625 sheet liners to cover repaired weld areas or the use of alloy clad steel plate in the initial digester fabrication.
One of the oldest applications of nickel alloys ran the pulp and paper industry is alloy K-500 doctor blades. Alloy K-500 provides high corrosion resistance with the abrasive and wear resistance needed for good service even in wet creping operations.
The bleaching circuit and pollution control areas are the most demanding corrosive environments in the pulp and paper mill process. Alloys needed in this area must be resistant to oxidizing conditions of high-temperature low-pH liquors containing chlorine, chlorine dioxide, oxygen, hypochlorate, peroxides, and chlorides. Only the high-molybdenum alloys 625, C-276, and C-22 have the required corrosion resistance to resist these aggressive liquors. In equipment used to clean off-gas from the recovery boiler, alloys 825, 625, G, and C-276 have been used, depending on the severity of the conditions. Typical conditions found are acid mists, low-pH liquors containing chlorides and organics, and sometimes high temperatures. Alloy G scrubbers have given more than 10 years of good service at one pulp and paper mill. Other plants have used alloys 625 and C-276 for internal components of scrubbers, fans, ducting, and so on.