Several explosions within the past couple of years -- responsible for killing or maiming more than 50 people -- involved the startup of natural gas-fired equipment. As consultants, we have been involved in the aftermath of several of these incidents, trying to get plants running again. In reviewing the root causes of these events, we’ve concluded there is a huge misunderstanding about how special repairs to gas piping are, and how careful one must be when starting up new equipment.
This article seeks to provide the basics regarding codes that apply, basic techniques that must be followed, and hazards to avoid. This is a special area of practice that must be respected. Natural gas piping installations and repairs are not like any other piping repairs. They can be done safely if simple principles are followed. If these are not followed and not respected, the results can be devastating.
Several codes and standards apply to these kinds of situations, including OSHA 1910, NFPA 54 and equipment standards such as NFPA 85 or NFPA 86.
Two codes that apply to gas equipment startups are OSHA 1910 and NFPA 54. The first, OSHA 1910.147, addresses lockout/tagout (LOTO) of energy sources. A lot has been written about this code, and most people follow it conscientiously, at least on the electrical side. Unfortunately, for gas piping, steam and other things that could be dangerous in a pipe, it is complied with much less often. As consultants in a facility, for instance, we often have found a lock on a disconnect and a gas valve closed but not locked.
Even when people try to perform gas piping lockout/tagout correctly, we find they often do not understand the issues surrounding lubricated plug valves and their need to be sealed to hold properly. In the case of a plug valve, which represents 60 to 80 percent of all natural gas piping system valves, there is a space between the plug and the body. If sealant is not applied annually, as required by code, gas will leak past the plug and body even when they are in the closed position. We find that most plants do not have the knowledge or equipment to seal these and have never sealed them in the life of the valve. Hence, closing or locking out a valve in this condition does not necessarily isolate the energy source.
The second code that applies is NFPA 54, which also is called the National Fuel Gas Code. We have found that many firms have not heard of it and do not understand it. The lack of isolation points such as blanks, blinds and pancakes, and the lack of purge points installed in most industrial plants, supports this viewpoint. There seems to be little forethought given to the actual installation of the gas pipe, how the gas pipe will be put into service, and the equipment started up.
To help illustrate the points outlined in the codes, here are 10 common gas piping and equipment startup hazards as well as suggestions on how to avoid a problem. Of course, these tips and techniques should be incorporated into a comprehensive, documented procedure for natural gas piping purging, piping system design and equipment startups.