Nickel Washers

The material family of nickel washers is not limited to pure nickel. Nickel-copper alloys such as Monel 400 and nickel-chromium alloys such as Inconel 600 are also widely used in specific corrosive media. According to ASTM B164 regulations for Monel 400 rods, its average linear expansion coefficient in the range of 20 to 300 degrees Celsius is 13.9 microns per meter per Kelvin. Compared with 12.5 microns per meter of ordinary carbon steel, this higher thermal expansion rate allows the gasket to adhere more closely to the flange surface when it heats up, thereby compensating for the loss of pre-tightening force caused by the thermal elongation of the bolt. At the same time, based on the NACE MR0175 standard's suitability assessment for hydrogen sulfide-containing environments, Monel The stress corrosion cracking threshold stress of 400 under sour oil and gas field conditions is as high as 240 MPa, which is much higher than the 150 MPa of austenitic stainless steel under the same conditions. Therefore, this type of gasket is preferred for use in sour natural gas processing equipment and submarine manifold connections. Its excellent pitting corrosion resistance has also been verified in simulated seawater full immersion tests, and the annual corrosion rate is less than 0.005 mm.

In terms of mechanical behavior and assembly control, the friction characteristics and elastic recovery ability of nickel washers directly affect the long-term stability of the fastening system. According to the DIN 946 standard method for measuring the friction coefficient of fasteners, the typical value of the friction coefficient of the bearing surface paired with a nickel washer and a stainless steel bolt is from 0.15 to 0.22. This lower range allows a higher pre-tightening force to be obtained under the same torque. For example, when an M16 bolt is tightened to 200 Nm, the pre-tightening force can reach 65,000 N, which is about 12% higher than that of a carbon steel washer. In addition, according to the ASTM E9 compression test, the nickel gasket produced an elastic deformation of 0.01 mm under the initial preload force, and the permanent deformation after unloading was only 0.01 mm, indicating that it has excellent resilience and can compensate for thread relaxation caused by cyclic loads. Long-term fatigue testing also showed that under an alternating load with an axial stress amplitude of 120 MPa, the supporting surface of the nickel gasket remained free of wear and peeling after three million cycles. This durability enables it to maintain the sealing specific pressure and reduce the number of regular retightenings in the connection between the compressor piston rod and the turbine casing, thus significantly improving the safe operation cycle of key rotating equipment.

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