Operating valve accessibility

Estimate acceptable air leakages resulting from leakage around static and rotary seals, valves, access ports, and other items of mechanical nature required for process operation from the following equations and the specific leak rates 0 indicated in Table 6-8, which is based on w < 10 lb/hr. 

The inventory of contained liquid and gas can be calculated between isolation points to determine the amount of material that can be released for pro-cess-related scenarios. The time frame to close manual valves—depending on accessibility, operating conditions, and availability of personnel—is typically 10-30 minutes. For remotely operated valves actuated from the control room, 60-90 seconds is used for isolation. The release rate will decrease based on the pressure decay of the system once the system has been isolated. 

Examples of common safe practices are pressure relief valves, vent systems, flare stacks, snuffing steam and fire water, escape hatches in explosive areas, dikes around tanks storing hazardous materials, turbine drives as spares for electrical motors in case of power failure, and others. Safety considerations are paramount in the layout of the plant, particularly isolation of especially hazardous operations and accessibility for corrective action when necessary. 

The sphere is held at sufficient height (A) to allow easy access to all of the control and operational valves (B), which in general operation... 

There are many kinds of control valves. Mechanical valves must be accessible to the operator s hand electrically operated valves permit remote control of flow. For tractors or self-propelled sprayers with enclosed cabs, the remote-controlled valves permit all hoses carrying pesticides to be kept safely outside the cab. 

A useful human factors exercise is to conduct a Valve Criticality Analysis. Typically, manually operated valves are organized into categories such as operated daily, operated occasionally, and used only during turnarounds. The category selected will determine the location and accessibility of the valve, with those that are used daily being provided with easy access that does not require any stretching or the use of ladders or other temporary equipment. 

The question may arise because there are so many PHAs, why is there a need for HAZID Before answering, one thing should be kept in mind there is no conflict between PHA and HAZID. In fact many PHA may be utilized in HAZID for identification hazards. This question is best answered with the help of an example. Suppose there is a manually operated valve (maybe locked open) in a pipe line handling corrosive material, situated at a height. The valve is never/hardly operated and kept open all the time. To access the valve, there is a cat ladder. If there is a seat... 

O Are manually operated valves and switches controlling the operation of equipment and machines clearly identified and readily accessible ... 

On this tank, the LAFIFI includes a trip function to terminate the transfer. For a well-designed and maintained safety instrumented protective system, a response time of two minutes between activation and complete cessation of flow into the tank is claimed. This includes the time needed to take urgent action in case the trip action is not successful - in this case to immediately close another remotely operated valve, readily accessible in the control room (the system having been designed for this emergency closure). 

Operation Valves, instruments, and many types of equipment require frequent attention for operation. These items must be accessible without impairing dte safety of plant personnel. 

Operating valves that carmot conveniently be located below a centerline elevation of 6 ft 9 in (2,050 mm) from grade or platform must have chain operators, extension stems, or motor operators. Except for battery limit valves, all unit isolation valves must be located at grade. Exhibit 2-6 highlights the minimum requirements for operator access to controls,... 

Shut-off valves at utility headers are located inside the rack area in the horizontal position, directly above the header if room permits. Operating valves must be accessible from platforms or by chain operators. The location of the valve must also permit the chain to fall free of obstructions that would hamper operation. An additional 20% of space must be allowed for future pipe rack growth. An alternative approach to such expansion is shown in Exhibit 11-13. 

Valve access catwalks can be seen in Exhibit 15-22. It is of utmo.st importance to give operations personnel adequate access to primatv- tank valves, Consider-... 

A bullet-tank piping layout is shown in Exhibit 15-43. Tanks are. set at the lowest possible elevation to. satisfy- pump head requirements. A catwalk is located across all four tanks to provide. sufficient access to operating valve.s and instruments. Liquid outlet piping to the pumps should allow for differential. settlement and line flexibility. A fire water. spray proteaion. system for bullets is. shown in Exhibit 13-36. 

Category 3 valves are used infrequently and are not critical to safe operations. Permanent access to these valves is not required it is acceptable to use mobile platforms, lift cages, or scaffolding to gain access to them. (However, portable ladders should not be used.)... 

Provisions should be made for clearances between piping and vessels, piping in pipe racks, pipe flanges, and other equipment, expansion loops, headroom above access routes or access platforms, accessibility for suitable support points, valve orientation, operation and accessibility, and clearance to permit removal of in-line equipment with minimal dismantling of equipment. 

Process safety and operability are checked — for example, orientation of relief valves, fail safe systems, orientation of non-return valves, access to valves and adequate provision of drains and vents. The plant is finally checked for cleanliness, removal of construction debris and so on. 

Multielevation piperacks are usually needed to handle all the required services for piping, electrical, utilities, and instmmentation. The two-level rack is one of the most common but three-level ones are also used. The utility lines are usually mn in the upper level and the process lines in the lower levels. The larger-diameter lines are located to the outside of the rack to be closest to the column supports. Access platforms are required at the battery limit to provide operators access to the block valves and blinds. If long mns of hot pipe are required, a portion of the pipe rack needs to be dedicated to an expansion loop. A horizontal space in the piperack is provided for a set of lines to be flat-turned into a set of expansion loops with the large pipes located on the outside. AH of the pipe turns are in the same horizontal plane, which is an exception to normal piping practice. A flat turn takes up and blocks space for other pipes. Flat turns are generally only made from the outside of the rack to minimize this blockage. 

Sampling locations for the unit test should be readily and safely accessible. The sample gatherer should be able to easily access the sample point. An isolation valve should be installed at the location. If a blind is installed, this should be modified in advance of the test. The sample locations shown on the P IDs must be compared against the actual locations on the equipment. Experienced operators may provide insight into the suitability of the location in question. 

At high pressure experiments the reactor should be installed in a pressure cell. All check valves before it, and the filter with the flow controller after it, can be kept in the vented operating room. As a minimum, the bypass valve and the flow controller must be accessible to the operator. This can be done by extended valve stems that reach through the protecting wall. Both the operating room and the pressure cell should be well ventilated and equipped by CO alarm instruments. 

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