TPi November 2016

Extending the service life of globe valves By Arc Energy Resources, UK

of globe valve manufacturers to apply the coatings more cost effectively. These techniques are also improving the protection performance and the efficiency of the valves. Commenting for Arc Energy Resources, managing director Alan Robinson said, “We have been applying corrosion- resistant coatings to equipment in the oil and gas industry throughout the world and have been aware of the difficulties with globe valves for some time. However, following an investment in two specialist welding machines, which we bought specially to handle the difficulties mentioned, we have already coated globe valves from 12" to 24". Since installation, these machines played an important part in the initial planning for globe valve contracts and have applied anti-corrosive coatings to the first batch of globe valves in an important current contract.” The specialist welding machines extend the size and scope of corrosion-resistant coating contracts that Arc Energy Resources can handle. The automated machines manipulate

As cast components, globe valves can be produced in virtually any shape required. In addition, inlets and outlets are designed with a constant cross sectional area that allows the flow of material to remain uniform. In effect, this means that inlets can be round to match the pipes delivering the flow of material, but then can change to an elliptical shape of the same cross sectional area, to maintain the compact dimensions of the valves in order to optimise flow within the valve. Globe valves are linear motion valves and are commonly used as on/off valves and as throttling systems for both gas and liquid systems. The gradual change in spacing between the disk and seat ring gives the globe valve good throttling ability as long as the pressure and temperature limits are not exceeded, and the process does not require special materials to combat corrosion. However, it is generally acknowledged that globe valves contain inherent cavities that can easily promote contamination and allow slurry material to become entrapped in the body of the valve, disabling its operation. This often prevents globe valves being specified for high purity or slurry systems. As globe valves are castings and can therefore be made to any shape the customer wants, designers generally try to keep the inlets and outlets at a constant cross sectional area, so that the flow is uniform. As mentioned earlier, this means valve inlets are circular to match incoming pipework, and then change to an elliptical section of the same cross-sectional area, which keeps the valve dimensions compact. When a globe valve is cast, the internal shapes are generally created naturally. However, service and repair can cause future problems, as applying anti-corrosion coatings for long-term protection can be very difficult due to the complicated shapes created by a valve’s internal geometry. While it can be difficult to apply anti-corrosion coatings to the internal surfaces of castings, weld overlay cladding specialist Arc Energy Resources has successfully applied its specialised coatings to globe valves for companies such as Masilinia Dresser and Severn Glocon and has, more recently, developed special techniques with the cooperation G lobe valves, which are used for regulating flow in pipelines, consist of a movable disk-type element and a stationary ring seat in a generally spherical body. They are named for their spherical body shape, with the two halves of the body separated by an internal baffle.

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