Flow control

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Vanessa triple offset valve undergoes cryogenic testing to ensure safe operational parameters are met.

Petrochemicals Middle East investigates what the regional boom in downstream developments means for the local and global valve suppliers.

Controlling the flow of fluids and gases through a petrochemical plant is a job which falls to the valves producers. In every plant, whether it produces basic chemicals, intermediates or polymers or even specialty chemicals, regulating the flow is vital to smooth operations and quality end-products.

Valves can be operated manually or automatically driven by changes in pressure, temperature or flow. These changes may act upon a diaphragm or a piston which in turn activates the valve, examples of this type of valve found commonly are safety valves fitted to hot water systems or steam boilers.

Although many different types of valves are used to control the flow of fluids, the basic valve type suitable for the petrochemicals sector can be divided into two groups: stop valves and check valves.

In addition, many specialised valves, which are not easily classified, are found in the engineering spaces. "There is a wide variety of valve types used within the petrochemical industry. The valve selection is dictated by the application. Primarily the valves are used for isolation, control and safety relief within the petrochemical plant and also to control and contain the process safely within the design limits of the plant," says Christophe Melinette, managing director Tyco Flow Control Middle East.

Plant valves

Stop valves are used to shut off or to stop partially the flow of fluid, controlled by the movement of the valve stem. Stop valves can be divided into four general categories depending on its functionality and shape of the valves where we have globe, gate, butterfly, and ball valves. The list also includes plug valves and needle valves which may be considered as stop valves. All these varieties of valves can be used in the petrochemical industry.

"The valves and specific valve manufacturers like Tyco selected for use within a petrochemical plant will have a well proven track record for efficient design, high quality products and proven reliability," explains Tyco's managing director.

Standards

Valves in petrochemical and refining installations are subject to numerous standards and specifications issued by many supporting organisations.

"Specifications are determined by the end user and the engineering contracting houses that design and build the plants. As safety is the number one priority in all industries you will find that the specifications have evolved greatly over the years. These changes are based upon operational experiences, advances in materials technology, design philosophy and improved manufacturing methods," adds Melinette.

"Specifications are generally customer driven and are written incorporating internationally accepted standards generally either ASME, DIN, JIS, API and ISO are used," explains Hassan Fazel, technical sales manager - Middle East region, at R S Clare and Co. Valve design in the last 50 years has typically used the valve standard of the American Petroleum Institute (API) for refinery use, known today as API 600, - affectionately known as the bolted bonnet steel gate valves for petroleum and natural gas industries standard.

The standard includes some criteria of testing which outlines that valves should not leak when they are subject to hydrostatic seat test, where the valve is subject to 1.1 times cold working pressure leak test.

Currently, valve manufacturers aim to achieve a zero closure test leakage rate during initial factory testing of their metal seated gate and globe valves.

Design integrity

The integrity of valve is very important and requests a lot of attention. "in order to control the whole flow with all the chemicals involved inside it is important to keep the integrity of the valves through, we have advanced products which we inject inside the cavity of the valve in order to seal and to keep the integrity of the valve and prevent it from corrosion" says Fazel.

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