Incorrect valve

Interactions refers to any jobs, tasks, or operations carried out by people who could directly or indirectly cause the hazard to be released. Direct interactions with the plant might involve breaking open pipework, opening reactors, etc. Indirect interactions would include remote activation of valves from a control room, or the performance of maintenance on critical plant items. Errors that might occur during these interactions could allow the harm potential to be released. This could occur directly (for example, a worker could be overcome by a chlorine release if an incorrect valve line-up was made) or indirectly (for example, if a pump bearing in a critical cooling circuit was not lubricated, as in the example in Chapter 1). The procedure as described above... 

Figure 3.12 Generic illustration of incorrect valve designs for the case of horizontal flow. In these examples only part of the cross section of the stream is sampled all of the time intermittent sampling/signal acquisition is in no way better, see Figure 3.11. The sampling valves shown there offer no counteraction for gravitational segregation and/or flow differentiation effects. All solutions shown are structurally incorrect. A specific valve opening design alone does not eliminate IDE.

Sizing a control valve for liquid-gas mixtures introduces incorrect valve coefficient, C, if for each of the two fractions is calculated separately, and then added. This method assumes that the liquid and gas are passing through the valve orifice independently and at greater different velocities. 

According to the chemical safety alert Hazards of Delayed Coker Unit (DCU) Operations (US EPA, 2003), some actions have been reported as beneficial to diminish the occurrence of incidents associated with incorrect valve activation due to mistaken coke drum or module identification. Some of the actions Usted in the referred safety alert are provide interlocks for valves that are manually operated as part of the switching/decoking cycle to avoid unanticipated valve movement provide interlocks for automated or remotely activated valve switching systems . These recommended actions can be achieved with the definition of set of permissive logics to prevent inadvertent valve operations. This set of logics can serve as an automated decision support system for the coke drum cycle. 

No one system has proven effective in eliminating all incidents associated with incorrect valve activation due to mistaken coke drum operation (US EPA, 2003). However, the development of a set of permissive logics that prevent inadvertent valve operations during the coke drums batch steps has been an improvement adopted by some refiners. But, once the permissive logics matrix is developed (based on operational procedures), it is important to define what type of accident scenarios these logics can prevent and the availability required for those logics which will need to be defined as safety instrmnented functions. 

Plant personnel performed a review of the temperature and pressure rating of the available check valve with Good Intentions. Not only was the valve suitable for the temperature and pressure but it was also constmcted with a better alloy for the service. Unfortunately maintenance persoimel were not aware of the missing piece of information from their database and endorsed the incorrect valve as replacement in kind. 

For most pneumatic controllers, the valve position shown in the control room is only an indication of the air signal that the controller is transmitting to the control valve. The control room instrument does not normally receive any feedback from the control valve. So, what factors influence a control loop to cause an incorrect valve position to be shown on the control panel ... 

Avoiding Incorrect Assembly Plants should be designed so that incorrec t assembly is difficult or impossible. For example, compressor valves should be designed so that inlet and exit valves cannot be interchanged. 

Status Clear It should be possible to see at a glance if equipment has been assembled or installed incorrectly or whether a valve is in the open or shut position. For example-. 

Incorrect Label materials, lines, pumps and valves chemicals used.. Check labels against batch sheets Set valves to correct flow path Use double check system Use procedures and training Use different packaging for different chemicals API RP 750 CCPS G-3 CCPS G-22 CCPS G-30 CCPS G-33... 

No discharge pressure. Pump improperly primed. Inadequate Speed. Not enough NPSHa. Plugged impeller or piping. Incorrect rotation. Closed discharge valve Air aspirated or air pockets at the suction line. 

Incorrect pressure control valve set- wheels, causing unbalance. 

The following descriptions are meant to briefly describe the various generic valve types. Within each type there are numerous different design details that separate one valve manufacturer s valves from the ne of these speciuc models have good points and bad points all can h correctly and incorrectly. It is beyond the scope of this book to c each valve manufacturer s design. However, the various valve sal will be more than pleased to contrast the benefits of their valve s ft with that of the competition. The reader is cautioned that hight valves do not necessarily mean better valves, and that expensive can result in a significant waste of money when a less expensive but adequate valve will perform satisfactorily. 

The pump had been awaiting repair for several days when a permit-to-work was issued at 8 a.m. on the day of the fire. The foreman who issued the permit should have checked ahead of time that the pump suction and delivery valves were shut and the drain valve open. He claimed that he did so. Either his recollection was incorrect or, after he inspected the valves and before work started, someone closed the drain valve and opened the suction valve. When the valves were closed, there was no indication—on them—of why they were closed. An operator might have opened the suction valve and shut the drain valve so that the pump could be put on line quickly if required. 

The furnace had been lit in an incorrect way for many years before the isolation valve started to leak and an explosion occurred. Never say, It must be safe because we have been doing it this way for years and have never had an accident. ... 

To keep the sweeping-out or purge time as short as possible, the solenoid valve should be close to the burner, and it should close quickly. In addition, the line between the solenoid valve and the burner should not drain into the furnace. As in the previous incident, the furnace had been lit incorrectly for many years before an explosion occurred. 

Solvent that is incorrectly routed will contaminate other batches Clear indications that valve is fully closed. Checklist and training to emphasize importance of closing valve. Improved labeling of valves. 

Warning If valve settings are not returned to the closed position, incorrect additions will occur. 

Another example is a safety valve in standby service. If demands occur very infrequently, time-related stresses such as external corrosion may have a significant influence. Repeated demands in very dirty service could easily lead to faster degradation and failure, whereas repeated demands in lubricated service might actually enhance performance if the failure mode of interest is failure to open. Failure data based on time or demands can also be skewed if the relief valve is initially damaged or installed incorrectly. 

The signal from a suitable thermistor placed at the evaporator outlet will vary, depending on whether it senses dry refrigerant gas or traces of liquid. This can be used directly to control the current through a thermal element to modulate the expansion valve. This de vice usually has no separate adjustable controller and so cannot be incorrectly set (see Figure 8.10). 

Since excess pressure indicates malfunction of part of the system - usually a condenser fault or incorrect closure of a valve - the high-pressure switch should be reset manually, not automatically. 

Incorrect operation of pumps or valves, causing feed tanks to overflow with the loss of chilled or hot water... 

Err" signal errors are automatically shown on the LED display in the case of a defective pH electrode or faulty temperature sensor (Pt 100) and for incorrect buffer two set points can be set over any part of the pH, mV or 0° C scale, which when exceeded starts an alarm and/or allows readjustment of dosing valves or pumps via an interface circuit. 

Incorrect metallurgical valve leaked coke resulting in an explosion under the coker unit. 

Conventional nuclear reactors and advanced breeder reactors were America s primary energy strategy since the 1950s to resolve the fossil fuel problem but when a reactor accident occurred in 1979 at Three Mile Island in Pennsylvania, public and investor confidence in nuclear fission dropped. The accident was triggered by the failure of a feedwater pump that supplied water to the steam generators. The backup feedwater pumps were not connected to the system as required, which caused the reactor to heat up. The safety valve then failed to act which allowed a radioactive water and gas leak. This was the worst nuclear power accident in the U.S., but in this accident no one was killed and no one was directly injured. At Three Mile Island faulty instrumentation gave incorrect readings for the... 

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