Valves refinery piping

The basis for design overpressure described in this section is related to the ASME Boiler and Pressure Vessel Codes and ANSI B31.3, Code for Petroleum Refinery Piping. Compliance with these codes is a requirement, or is recognized as the equivalent of a requirement in many locations. Where more stringent codes apply, the local requirements must be met. Therefore, local codes must be checked to determine their requirements. For example, some countries do not permit the use of block valves underneath pressure relief valves, unless dual valves with interlocks are installed. Also, in some cases, 20% accumulation under fire exposure conditions is not permitted, and accumulation allowed may be lower than the ASME Codes. In the United States, the ASME Code is mandatory, since it is a requirement under the Occupational Safety and Health... 

The austenitic irons also show good corrosion resistance in caustic alkalis containing sulphides and mercaptans and have therefore proved useful materials for the construction of pumps, valves and piping in caustic soda regenerators in oil refineries. 

This code states that it covers all piping located within a refinery. Piping is defined as including valves. 

Figure 7-20. Recommended API-520 piping for safety relief valve installations. Reprinted by permission, American Petroleum Institute, Sizing, Selection and Installation of Pressure Relieving Devices in Refineries, Part ll-lnstallation, API RP-520, 3rd Ed., Nov. 1988.

The networks that interconnect various process units and vessels to the discharge zones or flares occur widely in refineries and chemical plants. Figure 11 shows a typical configuration in which the root represents the flare, the terminal vertices represent the relief valves, and the edge (each labeled with an arabic numeral) represents a pipe section between two physical junctions (valves, flare, or pipe joints). The configuration of such a network is dictated by the layout of the process unit. In this discussion both the lengths of the pipe sections and the interconnections will be treated as specified variables. 

Conduct an inspection of petroleum refinery systems for leaks. For example, check hoses, pipes, valves, pumps, and seals. Make necessary repairs where appropriate. 

Both the failure of the isolation valves to hold and the difficulty in draining the system were due to solid build up in the circuit. In the previous two-year period, the refinery had changed its crude feedstock resulting in operating difficulties on the unit desalter. Carryover of salts led to accelerated corrosion in the crude column and associated piping circuits. 

F.L. Evans, Equipment Design Handbook for Refineries and Chemical Plants, Gulf, Houston, 1979, Vol. 2 piping, pp. 188-304 valves, pp. 315-332. 

Thirteen of the twenty-seven major refinery incidents reported from 1980 to 1995 in the large property damage report were piping failures. Six of twenty-four major petrochemical plant major incidents were the result of tube or piping failures or improper maintenance procedures involving valves. Recent examples of piping failures which resulted in massive fires or explosions follow. 

While epoxy resins are known for excellent chemical resistance properties, the development and commercialization of epoxy vinyl ester resins in the 1970s by Shell and Dow offered enhanced resistance properties for hard-to-hold, corrosive chemicals such as acids, bases, and organic solvents. In conjimction with the development of the structural composites industry, epoxy vinyl ester resin composites found applications in demanding environments snch as tanks, pipes and ancillary equipment for petrochemical plants and oil refineries, automotive valve covers, and oil pans. More recently, epoxy and vinyl esters are used in the construction of windmill blades for wind energy farms. Increasing requirements in the composite industries for aerospace and defense applications in the 1980s led to the development of new, high performance multifunctional epoxy resins based on complex amine and phenolic structures. Examples of those products are the trisphenol epoxy novolacs developed by Dow Chemical and now marketed by Huntsman (formerly Ciba). 

The process vessels were uprooted in 1955 and shipped to the Amoco Refinery in Texas City. Odd bits of piping and valves have sunk into the swamp. A half century of gentle, but persistent effort by Mother Nature has partly reclaimed this bit of earth for the natur world. 

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