Valves processing facilities

Process Facilities 15 Area electrical classification 16 Accessibility for mechanical integrity (sampling, maintenance, repairs) 17 Protection of piping and vessels from vehicles and forklifts 18 Protection of small-bore lines, fittings from external impact, personnel 19 Routing of process piping, critical controls cable trays, critical utilities 20 Vent, drain, and relief valve discharge locations... 

Industry literature typically cites concern with open air explosions when 4,536 kgs (10,000 lbs.) or more of flammable gas is released, however, open air explosions at lower amounts of materials are not unheard of. When the release quantity is less than 4,536 kgs (10,000 lbs.), a flash fire is usually the result. The resulting fire or explosion damage can cripple a hydrocarbon processing facility. Extreme care must be taken to prevent the release of hydrocarbon from vessels resulting in vapor releases and resultant blast overpressure. Measures such as hydrotesting, weld inspections, pressure control valves, adequate pressure safety valves, etc., should all be prudently applied. 

All fixed fire suppression system control valves should be located out of the fire hazard area but still within reach of manual activation. For high hazard areas (such as offshore facilities), dual feeds to fire suppression systems should be considered from opposite areas. For onshore facilities, firewater isolation valve handles should not be contained within a valve pit or a below grade enclosure within the vicinity of hydrocarbon process facilities, since heavy process vapors travel from the process and may settle inside. 

Processing facilities have experienced several serious pipe trench fires. Contributing to the size of the fires were inadequate or plugged drains, lack of isolation valves, pipelines on the ground, or inadequate fire stops along the length of the trenches. Pipe trench fires can result in significant business interruption. 

A simple, sequential numbering system to identify SRVs may be acceptable for a small plant such as a batch-chemical processing facility with only a few dozen SRVs. However, for PPG s Lake Charles plant, a dual numbering system is used to keep up with 2,000 SRVs in service and several hundred additional SRVs in storage. The devices kept in storage onsite are used as spares or can be cannibalized for parts. Spare safety valves for critical equipment must be available. [8]... 

Gas turbines should be installed with automatic fuel shutoff valves. Locate cooling towers far away from process units. Whenever possible, maintain cooling water pressure more than process stream pressure, at the coolers. Install gas detectors at the top of cooling towers, and an automatic shutdown system for cooling tower fans, in case of gas detection. Boiler and other utilities should be located far away from process facilities so that they will not be exposed to fires and explosions originating in the process plants. Install deflagration or detonation arrestors in low-pressure fuel gas systems connected to atmosphere or fired systems. 

When possible, firewater mains should be arranged in loops around process facility and tank farms. Shutoff valves should be located to allow isolation of system segments for maintenance while stiU providing water for all facilities. The minimum water rate with a section of pipe out of service should be at least 60% of the design rate at design pressure for that area. A firewater header should be provided in each process facility area to serve hose stations. 

Pressure relief valves are a critical safety item in almost all process facilities. Pressure relief valves simply must work. This means that they must never be blocked in from the equipment item(s) that they are protecting. Yet their very criticality means that relief valves will have to be routinely isolated and/or removed from the system that they are protecting so that they can be maintained and tested— both for the pressure at which they open and, more rarely, for their flow capacity. 

Does the facility have a program for regular inspection and testing of process safety valves and other process safety devices including interlocks ... 

This chapter covers the design of facilities to handle equipment drainage and contaminated aqueous effluents that are sent for appropriate disposal blowdown drum systems to receive closed safety valve discharges, emergency vapor blowdowns, etc. and facilities for process stream diversion and slop storage. Also covered are criteria for selecting the appropriate method of disposal. Design of flares is covered in a subsequent chapter. 

The BSD can either shut down the entire facility, or it can be designed for two levels of shutdown. The first level shuts down equipment such as compressors, lean oil pumps, and direct fired heaters, and either shuts in the process or diverts flow around the process by closing inlet/outlet block valves and opening bypass valves. The second level shuts down the remaining utilities and support facilities, including generators and electrical feeds. 

Listed across the top of the matrix are the various shutdown valves in the facility. A mark in each box indicates the function performed by each device to assure that it protects the process component. By comparing the functions performed by each device to the mechanical flowsheet, it is possible for an auditor to quickly ensure that the process component is indeed isolated. 

IMAS has a facility called EXPLORE allows the analyst to specify which indicators (e.g., temperatures, pressures, valve settings) are present, and which are absent in a particular scenario. EXPLORE then traverses the various links in the mental model representation network and generates a report that simulates the worker s thinking processes. This form of simulation provides useful information to the analyst with regard to the worker s capability to achieve correct diagnoses. Embrey (1985) gives an example of these simulations for the mental model in Figure 4.13. 

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