The hazards with piping, hoses & valves

Keep in mind some common dangers before undertaking process hazard analysis

Process safety management standards require every plant management to identify and address hazards. Although every site presents unique risks, most of the hazards related to piping, valves and hoses are similar and, hence, it’s useful to point out common dangers before Process Hazard Analysis (PHA) meetings take place.

Here are some common hazards related to piping, hoses and valves:

A. PIPING:
1. Hydraulic hammer:
A sudden stop or start in liquid flow creates a sudden pressure surge that can damage the valves and, in extreme case, cause the pipe to burst. Hammer can take place in lines carrying low-pressure steam where if the vapour cools as it flows through the line, liquid gets formed in the lower section. Eventually, the amount of the liquid increases to block the line, thus creating the potential for a hammer. The PHA team can think of putting a restriction in the vent line, which would prevent the valve from closing too closely.

2. Pig launchers and receivers:
Pig launchers and receivers inherently pose risk as piping needs to be opened with maintenance personnel present in the area who may be exposed to toxic or flammable material in case pigging equipment is prematurely opened. Also, in larger lines, lifting a pig to put it into the launcher or remove from the receiver could result in it being dropped onto someone. One way of reducing these risks is by using interlocking systems that don’t allow the pig receiver door to open while the system is under pressure. Also, locating the receiver away from normal operations can help minimize the risk to people.

3. Underground piping:
Underground lines can be hazardous as they are not visible. The lines can get highly corroded if cathodic protection system isn’t installed. The PHA personnel should inspect and maintain the underground line properly.

4. HOSES:
Hoses are usually involved in accidents, as they are involved in short-term or temporary duties. There is a potential to release hazardous chemicals, especially during the start or at the end of an operation. Here are a few ways by which chemicals could be released:

a. Hoses and truck pull away:
If a truck connected to a tank moves away before disconnecting its hose, the chemicals could spill out. Measures such as having a secondary containment around the loading station, excess-flow valves on the truck and the tank and special operating procedures like removing keys from the truck until the operation is complete, etc., can help avoid such leakage.

b.Hose failure:
Overuse of a hose can result in flexing and abrasion and finally failure. They need to be regularly inspected and maintained and replaced promptly when required.

c. Backflow prevention:
It is crucial to install a device to prevent backflow (check valve). Else, hazardous chemicals may reverse flow through the hose into another area.

5. VALVES:
Here are the major hazards that arise with valves:
a. Blocked-in pressure relief valves: 
Pressure relief valves play a critical role in ensuring safety in almost all process facilities. They must simply work; meaning that they must never be blocked in from the equipment they are protecting. Yet, they must be routinely isolated for maintenance and testing. Ideally, a relief valve shouldn’t be removed until the equipment it is protecting is shut down, purged, depressurized and air purged. However, many companies allow block valves to be placed underneath relief valves so they can be removed while the equipment remain in service. It’s important that these block valves be locked in the open position during operations.

By adopting the following guidance, the risks associated with having block valves below relief valves can be minimized:

1. A bleed valve can be installed between the relief valve and the block valve.
2. Full-port gate valves for block valves should be used.
3. Ensure the block valves are locked open when the relief valve is being used.
4. Check the status of block valves frequently.

b.Vents and bleeders:  
Leakage of hazardous chemicals from a vent or bleeder is a common phenomenon. The cause of the leak can be from the vent or bleeder being inadvertently left open or not completely closed; corrosion in the internal part of the vent or bleeder valve; and a sample point not shut properly.

c. Another risk arises:
when someone working on a vent valve pulls it off the pipe to which it was connected; this may happen at a joint weakened by corrosion. Hence, it is crucial to ensure bleeder and vent valves discharge to a safe location and are properly maintained.  The PHA team should list all control valves that may be operated in manual mode They should keep a few questions in mind, such as why the valve is manual, what would happen if it were to switch to automatic and; is the valve part of a safety shutdown system? Operators may say they would move the valve to its fail-safe position but this is prone to human error. Only high integrity instruments and valves should be trusted.

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