ing value is related to fluid velocity and is greater for high velocities

Ing value is related to fluid velocity and is greater

This preview shows page 25 - 26 out of 36 pages.

ing value is related to fluid velocity and is greater for high velocities. Highly refined hydrocarbons, such as jet fuels, accumulate charges more rapidly than more conductive hydrocarbons, such as gasoline. However, the rate of charge buildup in buried piping systems handling jet fuels at a maximum flow velocity of 5 ft/sec is such that special grounding is not necessary. Static charges are generated at approximately the same rate in fiberglass piping and metallic pipe. The differ- ence in the two systems is that the charge can be more easily drained from a metal line than from a fiberglass line. Under the operating conditions encountered in most industrial applications, any static charge generated is readily drained away from the pipe at hangers or by other contact with the ground, and any small charge in the fluid is drained away at metallic valves and/or instrumentation lines. NOV Fiber Glass Systems manufactures an electrically conductive piping system that should be employed when static electricity is a critical design parameter. Occasionally in piping a dry gas at high velocity, a charge may build up on an ungrounded valve. If this charge is not drained off by humid air, it can shock personnel who come in contact with the valve. This situation can be easily remedied by grounding the valve. Bulk fuel-loading facilities, because of high fluid velocities, present a problem to both metallic and fiberglass pipe. Filters and other high sur- face area devices are prolific generators of static electricity at these facilities. Special grounding procedures may be nec- essary under these conditions. F. Steam cleaninG Short duration steam cleaning of epoxy fiberglass pipe is acceptable provided the following recommendations are adhered to: The piping system must be open-ended to prevent pres- sure buildup. The maximum steam pressure does not exceed 15 psig corresponding to a steam saturation temperature of ap- proximately 250°F. Contact a factory representative for specific product design information. The piping system design must consider the effects of the steam cleaning temperatures. In most cases the support spans will be reduced 15-35%. Contact the factory before steam cleaning vinyl ester or polyester pipe. G. tHrUSt BlocKS Thrust blocks are not required for NOV Fiber Glass System's adhesive bonded piping systems. Large di- ameter F-Chem O-ring pipe is not restrained and may require the use of thrust blocks. Consult the factory for specific recommendations. H. VacUUm SerVice Vacuum service may be a system design condition, or it may occur as the result of an inadvertent condition. Sudden pump shut off, valve closures, slug flow and sys- tem drain down are examples of flow conditions that re- sult in vacuum. They should always be considered dur- ing the design phase. Regardless of the source, vacuum conditions result when the external atmospheric pressure exceeds the internal pressure. The pipe wall must be capable of resisting this external pressure without buck- ling. Consult our product bulletins for specific external pressure (vacuum) ratings.
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