Emergency isolation valves

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. 

If water has to be drained regularly from liquefied flammable gases or other flashing liquids, and if a spring-loaded valve cannot be used, then a remotely operated emergency isolation valve (see Section 7.2.1) should be installed in the drain line. 

Many fires have been prevented or quickly extinguished by remotely operated emergency isolation valves. We cannot install them in the lines leading to all equipment that might leak. However, we can install them in the lines leading to equipment that, experience shows, is particularly liable to leak (for example, very hot or cold pumps or drain lines, as described in Section 7.1.2) or in lines from which, if a leak did occur, a very large quantity of material, say 50 tons or more, would be spilled (for example, the bottoms pumps or reflux pumps on large distillation columns). 

In all these cases, once the leak starts, particularly if it ignites, it is usually impossible to approach the normal hand-isolation valves to close them. Emergency isolation valves are discussed in detail in Reference 3, and the following incidents show how useful they can be. They can be operated electrically, pneumatically, or in some cases, hydraulically. 

Figure 7-5. An emergency isolation valve stopped a fire.

Note that the operation of an emergency isolation valve should automatically shut down any pump in the line and trip the fuel supply to any furnace. 

It would be going too far to say that no one should ever enter a cloud of flammable vapor to isolate a leak. There have been occasions when, by taking a risk for a minute, a man has isolated a leak that would otherwise have spread a long way and probably ignited, perhaps exploded. However, we should try to avoid putting people in such situations by providing remotely operated emergency isolation valves to isolate likely sources of leak. 

Fit a remotely controlled emergency isolation valve (see Section 7.2.1) in the drain line. 

After the fire, the pump (and others) was relocated in the open air, under a canopy, so that small leaks would be dispersed by natural ventilation. It was surrounded by a steam curtain to disperse larger leaks. This would not have been necessary if the pump could have been located more than 150 m from sources of ignition. Gas detectors were installed to give early warning of any leaks. Emergency isolation valves (Section 7.2.1) were provided so that the pumps could be isolated safely from a distance [9]. What happened when another leak occurred is described in Section 7.2.1 (d). 

The leak could have been stopped as soon as it was detected if an emergency isolation valve (Section 7.2.1) had been fitted in the pump suction line. On the rebuilt plant such valves were fitted on the pump suction lines, more combustible gas detectors and more extensive insulation were installed, plastic pump bodies were replaced by metal ones, and spillages were directed to collection pits. The plant was built in 1972, when these features were not common practice many improvements had been made since then, but they did not go far enough. Most of those made after the fire could have been made beforehand. 

The leak size can be reduced by using double mechanical seals or a mechanical seal and a throttle bush, the space between the two being vented to a safe place. Major leaks may still occur, however, due to collapse of the bearing or seal. LFG pumps should therefore be fitted with emergency isolation valves (see Section 7.2.1), particularly if the temperature is low or the inventory that can leak out is high. 

Remotely operated emergency isolation valves (see Section 7.2.1) should be fitted on filling lines. If the hose breaks for any reason, the flow can be stopped by pressing a button located at a safe distance. Reverse flow from the tank truck or car can be prevented by a check valve. 

Emergency blowdown valves are among those that should be tested regularly. Reference 5 describes in detail the measures necessary to test emergency isolation valves when very high reliability is needed. 

If the pump had been fitted with a remotely operated emergency isolation valve as recommended in Section 7.2.1, the leak could have been stopped quickly. Damage would have been slight. As it was, the unit shut dow n for five weeks. 

Because hazards are avoided, there is less need to add on protective equipment, such as interlocks, alarms, emergency isolation valves, fire insulation, water spray, etc., and the plants are therefore usually cheaper as well as safer. 

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. 

A chemical engineer may have a choice of inherent safety variables, such as quantity stored or process temperatures and pressures, or process safety measures such as emergency isolation valves or containment systems, all of which may greatly reduce the vulnerabilities or the consequences of intentional loss. These are in addition to traditional security measures, which may include physical security, background checks, administrative controls, access controls, or other protective measures. For a more complete discussion of the options, refer to the AIChE Center for Chemical Process Safety Guidelines for Analyzing and Managing the Security Vulnerabilities of Fixed Chemical Sites and other references.f... 

The emergency isolation devices should be arranged so that they can be fully function tested without affecting the process operation. This entails that a frill flow bypass should be installed at each emergency isolation valve. These bypass installations should be locked closed when not in service for functional testing the ESDV. 

Emergency isolation valves (EIV) should be located based one two principals (1) the amount of isolatable inventory that is desired and (2) protection of the EIV from the affects of external events. EIV valves are normally required to have a firesafe rating (i.e. minimal leakage and operability capability, Ref. Table 14). Valves and their actuating mechanisms should be afforded adequate protection when they are required to be located in an area that has potential to experience explosion and fire incidents. 

Subsea pipeline emergency isolation valves for offshore facilities are provided where a risk analysis indicated topside isolation may be considered vulnerable. They should be protected from ship impacts, anchor dragging, flammable liquid spills and heavy objects that may be dropped from the offshore facility. 

An active fire protection system requires some action to occur before it functions per its design intent. This action may be taken by either a person or control system. Examples of active fire protection systems are monitors, water spray systems, foam systems, emergency isolation valves, and ESD systems. 

Equipment such as pumps, compressors, tanks, and vessels associated with large inventories of flammable gas or liquid (>5000 gallons) should be provided with equipment emergency isolation valves to stop the flow of material if a leak occurs. For example, the decision to add emergency isolation valves to the inlet and outlet of a compressor is dependent on the flammability of the gas, its pressure, and the quantity of gas in the associated piping and vessels. 

First, safety critical systems must be reliable. These systems control releases in the event of accidents. It s necessary to have a critical analyzer, instrument and electrical system test program. This should consist of preventive maintenance and alarm and trip device testing for panel alarms, emergency isolation valves and other critical components. [7]... 

Figure 10-24 A chemical process operator witnesses the testing of an Emergency Isolation Valve below a sphere of flammable product.

Employers need to decide what type of release their own employees can reasonably be expected to handle. For small releases, the best action to take is often to find the isolation valves on either side of the release and to close them. For a major incident, operators need to close the unit Emergency Isolation Valves (EIVs). There is a balance here on the one hand, having a person move into a situation to close the valves puts him at risk. On the other hand, if he does not take prompt action, the small release may become bigger and could lead to many more... 

For vessels containing large inventories of liquid hydrocarbon or liquids above their autoignition temperatures (AIT), emergency isolation facilities should be provided. An emergency isolation valve should be provided on a vessel or column liquid outlet when inventories of flammable materials exceed values such as those shown in Table 12.3. 

---