1 Sample preparation and test method
1.1 The coating sample preparation test uses the valve core ball material 40Cr13 martensitic stainless steel as the spraying base material, with a size of 60mm 15mm; Its chemical composition (calculated by mass fraction, the same below) is 0.38% C, 0.62% Si, 0.80% Mn, 0.050% P, 0.030% S, 12.87% Cr. According to the test, the valve core ball has been quenched and tempered at low temperature, its structure is tempered martensite, and its hardness is 512~545HV0.2. The plasma spraying feed materials are nano-Al2O3-13% TiO2 and WC-12% Co powders, with the particle size of 50-500nm. The American Sulzer2MetCo atmospheric plasma spraying system and F42MB spray gun were used to prepare the coating. The thickness of both coatings was about 50.
1.2 The coating performance test uses Vickers microhardness juice to measure the Vickers hardness of the coating sample surface, and the sample is polished and polished. According to the provisions of ISO-4516-2002 Measurement Method for Vickers and Knoop Hardness of Metallic Coatings, the loading time is 5s, and the full load time is 10s. For which sample, five consecutive points are measured, and the arithmetic mean value is taken. The distance between two indentation centers or between any indentation center and the edge of the sample is not less than 3mm. The cross section morphology of the coating was observed by JSM-5900 scanning electron microscope (SEM) of Japanese JEOL company. The friction and wear test is carried out by MM Wl universal friction and wear tester. According to the provisions of ASTM-G99-2004 Pin on Disc Friction and Wear Test Standard, the upper sample is CY5SnBiM nickel base alloy (ASME standard material) pin (5mm 12.7mm), which is the valve seat material with high-speed nickel tungsten coating at the brush plating position, The lower sample is a 40Crl3 steel disk (60mm 15mm) sprayed with Al2O3-TiO2 and WC Co cermet coatings. Before the test, the samples are finely ground to make its surface roughness Ra be 0.2~0.3.

How to correctly install expansion joints
Before contraction, the contraction joint shall check its type, specification and pipeline configuration, and must meet the design requirements. For the expansion joint with inner sleeve, attention shall be paid to the difference between the direction of the inner sleeve and the moving direction of the medium. The hinge rotation surface of the hinged expansion joint shall be different from the displacement rotation surface. It is necessary to stop the "cold tightening" of the expansion joint. After the installation of the pipeline, the auxiliary parts used for pre deformation shall be removed
It is strictly prohibited to use the deformation of expansion joints to adjust the installation of pipes, avoid the normal function of expansion joints, reduce the service life, and increase the load of pipeline systems, equipment and supporting parts. During the installation process, welding slag is not allowed to splash on the surface of corrugated paper shell, without damaging the shell
After the installation of the pipeline system, the yellow auxiliary positioning components and fastener wave contraction joints should be removed as soon as possible and the limiting device should be transferred to the designated position according to the design request, so the pipeline system has sufficient compensation ability under the environmental conditions. All moving elements of the contraction joints are not interfered or restricted by external components, so as to ensure the normal movement of all moving parts
During the hydraulic test, the secondary fixed pipe support with expansion joint shall be strengthened to prevent the pipe from moving or rotating. For the contraction joint and socket receiving used in the gas medium, attention shall be paid to whether temporary supports can be added during the water injection. The 96 chlorine content of the water cleaning solution for the hydraulic test shall not exceed 25PPM
Scope of application and precautions: The shrink joint has good comprehensive performance and is widely used in basic projects such as chemical engineering, construction, water supply, drainage, petroleum, heavy industry, refrigeration, health, plumbing, fire protection, and power