Isolation valves storage tanks

We put a lot of effort into improving safety by adding protective equipment onto our plants, new and old gas detectors, emergency isolation valves, interlocks, steam curtains, fire insulation, catchment pits for LPG storage tanks, and so on. We also introduced new procedures, such as hazard and operability studies and modification control, or persuaded people to follow old ones, such as permits-to-work and audits. 

The incidents described could occur in many different types of plants and are therefore of widespread interest. Some of them illustrate the hazards involved in activities such as preparing equipment for maintenance and modifying plants. Others illustrate the hazards associated with widely used equipment, such as storage tanks and hoses, and with that universal component of all plants and processes people. Other incidents illustrate the need for techniques, such as hazard and operability studies, and protective devices, such as emergency isolation valves. 

Where process, safety, and environmental considerations permit, vacuum protection may be provided by properly sized ever-open vents. Alternatively, active protective devices and systems are required. Vacuum breaker valves designed to open and admit air at a predetermined vacuum in the vessel are commonly used on storage tanks, but may not be suitable for some applications involving flammable liquids. Inert gas blanketing systems may be used if adequate capacity and reliability can be ensured. Where the source of the vacuum can be deenergized or isolated, suitably reliable safety instrumented systems (e.g, interlocks) can be provided. 

The catalyst preparation area is positioned between the two polyethylene production units with 60 feet separating each one. The aluminum alkyls storage canopy and isopentane horizontal storage tank are located at a remote area at an approximate distance of 250 feet away from the production and utility areas. The isopentane is transported to the catalyst preparation area through a 3-inch pipeline. A remote actuated isolation valve on this supply line that fails closed is located at the isopentane storage tank. This control valve and an associated isopentane feed pump are managed by the operator in the control room. 

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. 

It is desirable and inherently safer to use fire-safe valves whenever it is necessary to isolate flammable or combustible fluids in a pipeline, tank, or other type of equipment. Fire-safe valves should be considered for handling most fluids that are highly flammable, highly toxic, or highly corrosive and that cannot be allowed to escape into the environment. Fire-safe valves should also be used to isolate reactors, storage vessels, and pipelines. They can be used wherever EBVs are required. 

Diked areas around refinery storage tanks are frequently provided with storm drains discharging into the trunk sewer. An overflow as the result of an overfilled or ruptured tank could discharge large quantities of oil to the refinery sewer and would ultimately overload the separating facilities. To prevent this and to allow recovery of the oil within the diked area, it is common practice to provide some type of valve arrangement to isolate the storm drains in tank fields from the trunk sewer. 

The steering committee should provide guidance as to how unused or abandoned equipment is to be analyzed. An unused storage tank, e.g., may have been declared as abandoned. Yet, if that tank can be filled with process liquids merely by opening valves, then it is not really abandoned, and so it has to be included in the analysis. True abandonment of equipment only occurs when the equipment (including all associated instrumentation and electrical equipment) is positively isolated and/ or disconnected. 

Any storage tank must be designed so that branches below the liquid level are kept to a minimum. These will normally be limited to a bottom outlet line and consideration should be given to providing an internal plug valve. An isolation valve should be bolted directly on to the tank branch with an automatic valve in the outlet line. 

The WWER-1000 plants are equipped with ECCS and containment spray systems that have a similar design basis and similar basic configuration as in western PWRs. These systems have 3 100% redundancy with the exception of the ECCS water storage tank which is common to all subsystems. The same tank serves as a containment sump. The tank is located under the containment and has open connections to the containment through the bottom plate. Each of the three safety system trains has one suction line from the ECCS water storage tank to the residual heat exchangers and further to the low pressure safety injection, high pressure safety injection and spray pumps. The suction line is equipped with one containment isolation valve. 

The configuration of the ECCS water storage tank can lead to loss of coolant during an accident, if there is a passive single failure in the tank itself, or in any of the three suction lines between the tank and the containment isolation valve. Such a failure occurring during LOCA would lead to severe core damage and bypass of the containment. 

The passive contaimnent cooling water storage tank outlet piping is equipped wifli three sets of redundant isolation valves. Failure of a component in one train does not affect the operability of the other mechanical train or the overall system performance. The feil-open, air operated valves require no electrical power to move to their safe (open) position. The normally open motor-operated valves are powered fi om separate redundant Class 1 dc power sources. 

Operation of the main control room habitability system is automatically initiated on high-2 particulate or iodine radioactivity set point, or low pressuriser pressure, a safety related signal is generated to isolate the main control room from the nuclear island non-radioactive ventilation system and to initiate air flow from the main control room habitability system storage tanks. Isolation of the nuclear island non-radioactive ventilation system consists of closing valves in the supply and exhaust ducts that penetrate the main control room pressure boundary. Main control room habitability system airflow is initiated by a signal which opens the isolation valves in the main control room habitability system supply lines (see Section 6.4 of Reference 6.1). 

The demineralised water transfer and storage system consists of the demineralised water storage tank, the demineralised water transfer pump, two catalytic oxygen reduction units and a condensate storage tank. The system has one contaimnent penetration, with isolation valves on either side. 

In containment refuelling water storage tank (IRWST), its injection lines, screens and isolation valves. 

Transfer Runs. During these runs the storage tank was pressurized to 100 psig as rapidly as possible at pressurization, three bottles were isolated from the gas manifold by closing their bottle valves. Pressure was then held at 100 psig for a total elapsed time of 60 seconds or longer, at which time three additional gas manifold bottles were isolated. Transfer was initiated at this point. At the completion of transfer, three additional manifold gas bottles were isolated. Pressure was held... 

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