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If your facility has a gas line running onto your property, there are new rules that will impact you, no matter what kind of business you are in.
|Fig. 1. Kleen Energy aftermath|
Spurred on by the recent explosions at the Kleen Energy power plant under construction in Middletown, Conn., and the ConAgra plant in Garner, N.C., the National Fire Protection Association (NFPA) has adopted more than 40 changes to the National Fuel Gas Code (NFPA 54). These changes outline new procedures for purging gas lines, a process which has led to numerous explosions, injuries and even fatalities in recent years, including six deaths and millions of dollars worth of damage at Kleen Energy this past February (Fig. 1).
It’s time that risk management and safety professionals better understand the unique design and safety requirements for working with and purging natural gas piping systems. Many do not realize that recent regulations have changed, prohibiting the release of natural gas into buildings when construction projects or maintenance events are occurring. According to the NFPA, the new requirements are designed to require outdoor purging for any industrial, large commercial or large multifamily building.
Other code changes prohibit the purging of gas pipelines by using natural gas – a common practice amongst utility companies – and change the way that purging events should be monitored on site. The complete list of changes is available at nfpa.org.
Misunderstanding Leads to Disaster
If you are planning to add equipment, commission it into service or even build a new plant in the U.S. or overseas, this is an issue you must pay attention to. The U.S. Chemical Safety Board reports that the purging process has been linked to at least seven major explosions since 1997 that have killed dozens and injured hundreds.
Whenever natural gas piping is installed, extended or repaired, it must be purged to remove explosive air/fuel mixtures. If natural gas is sent into a pipe containing air, it can create a spot in the pipe that has a flammable mixture. If this mixture moves toward a burner or ignition source, you have essentially made a pipe bomb.
Purging should not be confused with venting. The term venting is usually used to describe the release of gas when a piping section is opened and gas is allowed to be released to the surrounding area. This might occur from opening a flange, a union or a purge vent. Purging is different. It involves the use of an inert medium such as nitrogen to push gas out of the pipe to an endpoint. There are many different types of purges that depend on the flow rate and the velocity of the purge medium.
Gas piping design, operation and safety require a very specialized level of expertise. Those responsible for risk management need to make sure that everyone in their organization knows the rules and understands what needs to be done to protect your facility. Engineers and designers must be thoroughly trained in the code and practical design requirements for natural gas piping. Contractors should be especially cognizant of the safety requirements and worker training required when purging natural gas piping.
Current requirements are understood by very few. It is unlikely that even your property insurer will fully understand how to direct you. Compounded by the recent gas pipeline explosion in San Bruno, Calif., many companies and their insurers are no longer willing to take on the liability for purging gas lines without professional third-party support.
Recent events graphically illustrate the inherent hazards of improperly designed natural gas piping that is commissioned in a poorly planned and haphazard manner. Beyond the obvious risk of death and injury, explosions on the scale of the Kleen Energy disaster can cause extreme property damage worth hundreds of millions of dollars, cause significant lost production time and irreversibly damage a company’s reputation.
|Fig. 2. Fuel-train training simulator|
Planning a Safe Purge
In our experience, we have found that many designers, engineers, contractors and maintenance workers do not understand that natural gas piping repairs are quite different from the more familiar fluid or air piping. Therefore, they require special knowledge and training. There is often a huge and dangerous lack of knowledge among those who routinely manage or perform gas piping repairs (Fig. 2). However, if a good plan is prepared by engineering experts and the correct precautions are taken by the contractor, you can have an incident-free project.
Consider this short list of important tasks and key questions when planning a gas piping repair:
- Is there a written purging plan (pre-repair and post-repair) that identifies all of the pressure-testing needs and standards that must be complied with? Does everyone on the team understand the plan and the role they play in its execution?
- Has a gas reintroduction plan been prepared? Has reintroduction and start-up been discussed with the start-up team, including any unique hazards?
- Were the local emergency services or fire department involved in the planning? Is fire-fighting equipment centrally located for workers?
- Has the gas piping design been reviewed for mechanical issues, including piping materials, rated valves and fittings, purge points, and blinds? Where are the isolation points, and how will isolation be safely achieved?
- Is there a natural gas isolation and equipment lockout plan? Is there a plan for cleaning lines and retesting automatic valves after the project has restarted? Verify that all special shut-off valves are serviced. Verify that all piping is properly marked.
- Is (or should) the gas utility involved in the purge process? Do they have any special requirements?
- Have you determined the amount of nitrogen needed for the purges and leak checks and how it will be introduced to the piping system? Does everyone understand nitrogen hazards? Conduct safety training on the use of nitrogen as part of the planning process.
- Where will the purge be directed? What are the prevailing winds? Are there building vents or other equipment air inlets nearby? If a high-pressure pipeline blowdown or pressure release is to occur, modeling of the plume may be helpful.
- Are all electrical services secured in the area of the gas purge and where the venting of natural gas may occur? An explosion can only occur when an ignition source is nearby.
- The portion of the project site where gas purges take place should be cleared of all workers, except those performing the gas purge. Spectators should not be allowed.
- Document all of the pressure-testing results (i.e. test pressures and how long they were held).
|Fig. 3. Lockout of a manual valve|
What Codes and Rules Apply?
There are many codes that can have some application to natural gas piping repairs. As we’ve discussed, the main code that applies to natural gas piping is NFPA 54: The National Fuel Gas Code. The rules are rather lengthy, and it does take time and effort to fully understand the intent and requirements of the code and the recent changes. We often run across consulting engineering firms and contractors that do not understand the basic code requirements. This lack of understanding often appears with a plant design that lacks proper isolation points (e.g., blanks, blinds, pancakes) and/or purge points. There seems to be little forethought given to the NFPA requirements in the installation of the gas pipe or how the gas pipe will be commissioned after installation or inspected and serviced in the future.
Another important code to consider is OSHA 1910.147 for lockout/tagout of hazardous energy sources. Much has been written about these requirements and most workers make some attempt to comply with it – at least for electrical devices. However, the OSHA requirements also cover other plant systems, such as natural gas and steam piping. For instance, we often find a lock on electrical disconnects but seldom on a closed gas valve (Fig. 3).
Even when workers attempt to isolate equipment correctly, one area often overlooked is the lubricated plug valves used in gas lines. Lubricated plug valves, which represent 60-80% of natural gas piping system manual shut-off valves, have a small gap between the plug and the valve body. If a sealant is not applied annually, as required by code and the manufacturer, gas will leak past the plug even when the valve is in the closed position. We find that most facilities do not have the knowledge or the equipment to seal these and have never sealed them during the life of the valve. Hence, closing or locking out a valve in this condition does not adequately isolate the energy source. The more serious issue is that if these are not regularly sealed, the valve can become impossible to close. This means you may not be able to shut off the gas supply in the case of an emergency.
|Fig. 4. Who’s responsible?|
Controlling the Risks
So, whose job is natural gas piping and purging safety? The design engineers may prepare the drawings to the applicable codes and standards but may never even visit the project site. The project manager must ensure the project meets those codes and standards but is usually consumed with schedules and budgets. Contractors are focused on meeting the project specifications, staying on schedule and making a profit. The project safety director is usually worried about lockout, trip hazards, slips and falls, tie-offs and other more-common issues. Most city inspectors don’t understand the intricate details of gas piping commissioning because there aren’t any local ordinances with which the project must comply.
When the responsibility for safe natural gas pipe purging is everyone’s responsibility, then it’s no one’s responsibility (Fig. 4). In the most recent disasters very experienced people were conducting the work. But in the heat of battle, many things can and do get overlooked. There are countless daily stresses and pressures on a construction site. That’s why proper planning and commitment to safety from the top down is needed to provide the focused discipline that can make the difference between success and failure. IH
For more information: Contact John R. Puskar, P.E., principal with CEC Combustion Safety, 11699 Brookpark Road, Cleveland, Ohio 44130; tel: 216-826-3473; e-mail: email@example.com; web: www.combus tionsafety.com. He serves as an alternate on NFPA 86 and ASME CSD-1 committees and is also on the NFPA 85 and NFPA 56 committee.