Shutdown valves

In recent years much more attention has been given to pipeline isolation, after instances in which the contents of export pipelines fed platform fires, adding significantly to damage and loss of life. Many export and in field pipelines are now fitted with emergency shutdown valves (ESDV) close to the production platform, to isolate the pipeline in the event of an emergency. 

The expander is now ready to be put into operation. Open the compressor inlet valve and expander discharge valve simultaneously. Then open the compressor discharge valve. Make sure the variable nozzles are in the closed position. Push the start button on the control panel to open the inlet shutdown valve. 

These valves isolate the compressor. Most operators require both shutdown valves to be automatic. Some operators use manual valves on small onshore compres,sors. If the compressor is in a building it is preferable to locate the valves outside the building. 

FE aoW ELCMEHr FT ROW IHAMSUinER LC LEVEL CONTROL LSH. HIOH LEVEL SHUT DOWN PC PRESSURE CONTROL POT PRESSURE DtfrERENT A PSH HIGH PRESSURE SHUT (.OrVN PSL LOW PRESSURE SHUT UO.VN S.O.iSHUT DOWN SDV SHUTDOWN VALVE TC TEMPERATURE CONTROL TSITH GH TEMPERATURE SHUT DOWN... 

Suction and Discharge Shutdown Valves and Discharge Check Valves... 

As long as pressure, level, and temperature control devices are operating correctly, the safety system is not needed. If the control system malfunctions, then pressure, level, and temperature safety switches sense the problem so the inflow can be shut off. If the control system fails and the safety switches don t work, then relief valves are needed to protect against overpressure. Relief valves are essential because safety switches do fail or can be bypassed for operational reasons. Also, even when safety switches operate correctly, shutdown valves take time to operate, and there may be pressure stored in upstream vessels that can overpressure downstream equipment while the system is shutting down. Relief valves are an essential element in the facility safety system. 

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. 

HF is supplied from a 100-Jb cylinder on an electronic scale which has a 10-g resolution. The cylinder is heated to 37°C with a band heater with two integral temperature sensors, one for control and an independent one for shutdown in case of overheating. From the cylinder, the HF passes through a throttling valve, a backup shutdown valve, and a control valve. A continuous nitrogen flow (actually the cathode reference flow) was added downstream of the control valve. 

The second phase may involve a breakdown of a barrier function. A barrier function is a safety feature such as a shutdown valve or containment system, a procedure, or the communication system. AVhen these safety systems fail, the incident then evolves from an undesirable occurrence to a near miss and, if enough barriers fail, the incident could finally progress to a minor or major accident or operational interruption depending upon the consequences or circumstances. 

Technology—Designs that have a detrimental affect on performance include a piece of equipment meant to be used outdoors designed with data entry keys that are too small and close together to be operated by a gloved hand, or a shutdown valve positioned out of easy reach. 

Safety shutdown valves, which are normally wide open and operate infrequently, are expected to respond to a safety trip command reliably and without fault. To achieve the level of reliability required in this application, the safety valve must be periodically tested to ensure positive operation under safety trip conditions. To test the operation of the shutdown system without disturbing the process, the traditional method is to physically lock the valve stem in the wide-open position and then to electrically operate the pneumatic shutdown solenoid valve. Observing that the pneumatic solenoid valve has properly vented the actuator pressure to zero, the actuator is seen as capable of applying sufficient spring force to close the valve, and a positive safety valve test is indicated. The... 

FIG. 8-86 Online partial stroke diagnostic used to validate the operability of a pneumatically operated safety shutdown valve, (a) Input command generated by the diagnostic and resulting travel, (b) Actuator pressure measured over the tested range of travel. 

The primary system is intended to isolate the major equipment in order to prevent reverse flow and exhaust oxides in a gaseous state. It consists of a special restraint type valve (check) and two motorised shutdown valves, arranged in series. The system includes a low pressure detector on the main pipe that trips the sulphuric acid pumps, isolates the process and stops the helium flow into the reactor and heaters (emergency system EAS-200). 

Class 1 safety instrumentation loops include alarms and trips on storage tanks containing flammable or toxic liquids, devices to control high temperature and high pressure on exothermic-reaction vessels, and control mechanisms for low-flow, high-temperature fluids on fired heaters. Other Class 1 instruments include alarms that warn of flame failure on fired heaters, and vapor detectors for emergency valve isolation and sprinkler-system activation. All of these alarms, shutdown valves, and other critical instruments are regularly proof-tested to a well-defined schedule. 

If the situation arises which requires an instrument to be out of service for a very short period of time such as an instrument mechanic is freeing-up a stuck shutdown valve with the operator present or temporarily pulling alarm cards to help identify mystery alarms, etc. In these cases, the lead operator should be informed and the operator gives his undivided attention to the problem, but an out-of-service tag may not be filled out. 

Low pressure gas line is plugged. Loss of fuel for heater and Instrument gas supply Total shutdown Valves are fail safe, ESO occurs ... 

Many consider the use of a conventional PLC for safety applications. In Case 2 a proposed design using a general purpose pressure transmitter, a conventional PLC, a three way solenoid and shutdown valve is being considered. The design is entered into the SIF verification tool and the results are shown in Table 12-3. 

Considering the architectural limits, the 3-way solenoid and the shutdown valve are Type A devices. The transmitter and the PLC are both Type B. A summary of SFF calculations and architecture limits are shown in Table 12-4. 

Figure 12-4 consists of a single Safety Transmitter, safety PLC, and single shutdown valve without tight shutoff requirements with a digital valve positioner. The digital positioner would be provided with the capability for Partial Stroke Testing (PST). 

Figure 12-6 consists of two conventional Transmitters (loo2 voting), a safety PLC, and two separate shutdown valves (loo2) with individual solenoids. 

In Figure 12-6 the third proposed design is shown. This case consists of two conventional transmitters (loo2 voting) with comparison diagnostics, a safety PLC, and two separate shutdown valves (loo2) with individual solenoids. The calculation results are shown in Table 12-7 using a common cause beta factor of 5% for the sensors and 10% for the final elements. 

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