Air and nitrogen as alternatives to natural gas for cleaning pipes in power plants
An accident happened in a power plant while pipe cleaning. Purging natural gas was used for cleaning and it is deemed to be the cause of the accident. The event motivated the recommendation of other alternatives that are already used in the sector: air, nitrogen or special cleaning devices.
Cleaning devices – cleaning pigs
Natural gas is a fossil resource, consisting mainly of methane (about 95%w), other hydrocarbons (C2-C4), nitrogen, carbon dioxide and traces of hydrogen sulphide and water. Methane is an extremely flammable gas, and can generate explosions. It is also a potent green house gas and precursor of tropospheric ozone.
Air is not hazardous in itself, but if pressurized, physical hazards have to be considered. Air may enhance the potency of fires, by providing oxygen.
Nitrogen is not included in the EU harmonised classification. It is generally considered a safe gas, under normal conditions (see Further Information).
One of the preparatory phases for new power plants is cleaning the pipes from debris and other contaminants that could damage the facility, for example when striking the turbines blades. It is common practice in gas energy plants that natural gas is used to clean the pipes.
During such an operation in a new built plant in USA, an explosion happened, injuring about sixty persons, six of which lost their lives. Cleaning with natural gas is deemed to be part of the accident cause. The ignition cause is not clearly identified. It could have been one of the debris generating sparks or, another source among the many that are generally present on an industrial construction site.
The event drew attention of the public and media, but also of authorities and safety specialists. The US Chemical Safety Board (CSB, an independent federal agency) ran an investigation concluding that the use of safer alternatives should be regulated or at least recommended by competent authorities and professional bodies.
Such alternatives may include air, nitrogen (a nonflammable gas), or using special cleaning devices (called pigs- see Further information). All these alternatives are already used in power plants.
Recommendations made by CSB following this accident were considered by professional bodies and local (state) authorities, some being accepted already, other still pending.
The substitution reduces the fire and explosion risks associated to the use of large quantities of natural gas which contains methane and other flammable substances. The alternatives are also ‘climate neutral’ while fossil methane increases the global warming potential even if it is flared.
– Nitrogen MSDS from Sigma Aldrich
– The Art of Pigging from Girard Ind.Further languages available
Type of information supplier
The description is based on ‘Pipe Cleaning Practices that Led to Kleen Energy Explosion Are Common Across Gas Energy Industry, Survey Data Show’ published by US Chemical Safety Board (CSB) in 2010, on their website.Type of publication and availability
Original document: click here
Publication or last update: March 2013