SEVERE SERVICE
Image 5: Hardness checking
a more suitable coating for severe service applications, such as flushing and thermal shock, than HVOF coatings. The fusing process of most Spray & Fuse coatings in the market is achieved by manually heating the ball seat with an oxyacetylene burner. This is highly dependent on experience, so it is difficult to guarantee temperature uniformity all over the ball set, which may lead to a coating with uneven quality. To obtain a reliable and highperformance coating, it is recommended to use a high-precision vacuum furnace which ensures a minimal temperature variation during the fusing process. Lapping plays an important role in producing high-quality coatings. Standard lapping processes only ensure sufficient roundness around the sealing area. If we extend the area of measurement to the whole ball, it may already exceed the tolerance requirements. This is why many metal-seated ball valves exhibit relatively acceptable performance during factory testing; however, unacceptable leakage occurs due to coating damage caused by just a few open-and-close cycles once the valve is installed. Therefore, in addition to spray capability, skilled lapping capability needed to ensure the ideal roundness all over the ball. Furthermore, a good lapping process will also guarantee an even coating thickness so that even hardness is achieved. Testing and verification check that coatings are produced to the desired quality, and also provide continuous improvement instructions. The coating inspection method used in the valve industry generally includes hardness, porosity and bond strength tests on specimens. However, it has limitations: the test results can only verify that the coating satisfies the criteria in international standards, and a coating verified on a specimen doesn’ t guarantee the same performance under real working conditions when applied to a ball set. An alternative solution can resolve this: test the coating performance under conditions simulating, but stricter than, the real valve working conditions, and use standard coating inspections as supplementary testing.
Summary
This article has discussed how hard coating can enhance the performance of ball valves, the challenges that severe service applications pose for ball valves, and some potential solutions. Although hard coating can extend a ball valve’ s working scope and improve its performance and lifespan in severe service applications, this strictly depends on the quality of the coating. Subquality coating is a problem that can quickly create issues with a ball valve, resulting in poorer performance than a soft-seated ball valve. Therefore, special attention must be given to the quality control of the coating to prevent unexpected situations.
About the authors Dai Guangzhou, Senior Engineer, GDai @ flowserve. com Henry Wang, Site Engineering Manager( Suzhou, Isolation Valves), HeWang @ flowserve. com Thorsten Hecht, Global Engineering Leader( Argus Valves), thecht @ flowserve. com Dr. Felix Tiggemann, Global Head of Surface Technology( Arguloy etc.), ftiggemann @ flowserve. com Jörg Hoenicke, Product Specialist( Argus Valves), jhoenicke @ flowserve. com
40 Valve World August 2025 www. valve-world. net