The growing use of gases that vary by type and/or source in transmission and distribution networks of gases (e.g. regasified LNG mixed into natural gas) is widening the challenge of managing naturally occurring radioactive material. Commonly known by its initials, NORM, this material can accumulate in scale, dust or sludge in pipelines and on equipment.
NORM in gas networks originates from the naturally occurring gas radon present in very small quantities in natural gas. When radon ‘decays’ through emitting radiation, it rapidly turns into other radioactive substances including isotopes (variants) of polonium (Po) and lead (Pb). The level of radioactivity from radon itself is halved every 3.8 days. The equivalent half-life figures for the radioactive isotopes Po-210 and Pb-210 are 138 days and 22.3 years respectively, making them a more persistent health risk when NORM is concentrated in pipeline systems.
Levels of NORM in piped natural gas can vary widely depending on the composition of the gas and where it was sourced. Radon levels vary in gas from different offshore and onshore fields. Consequently, they also vary in gas piped in from fields and in liquefied natural gas (LNG) produced from different gas sources. So, as operators begin to mix imported LNG with natural gas in pipelines, they are starting to see greater variation in NORM.
Other factors that influence NORM levels in pipeline scale include how much of the radon ends up in the scale, and the time taken for gas to transit from field to pipeline network. It is worth noting too that changing the gas mix may result in levels of NORM in scale increasing significantly in areas where it has previously only been found at much lower levels.
Health and safety considerations
The human body has evolved over millions of years to withstand to a significant degree the biological effects of naturally occurring radiation in the environment. Higher levels of such radiation can raise the risk to health, however.
The types of radiation from Po-210 and Pb-210 in NORM are low-energy forms that cannot penetrate skin. That said, they can be hazardous to health if the radioactive material is inhaled or ingested. Management of health risk is required where prolonged exposure to NORM and/or to high concentrations is possible. Furthermore, NORM-containing scale, dust and sludge can auto-ignite in some circumstances. This poses a fire and explosion safety risk in gas networks and in plants such as petrochemical facilities that use gas as a feedstock.
Industrial operations can concentrate NORM
Industrial operations including the processing, piping and liquefaction of natural gas can concentrate levels of NORM along the chain from wellhead to pipeline. In its 2008 guidelines for handling NORM in parts of the gas value chain, the International Association of Oil & Gas Producers reported radioactivity ranges globally of:
- 0.02–75 becquerels per gram (Bq/g) of Pb-210 in hard scale
- up to 2,000 Bq/g in soft/medium-hard scales
- 1,300 Bq/g in sludges accumulating in tank bottoms, gas/oil separators, dehydration vessels, LNG storage tanks, and in waste pits.
In transmission and distribution pipelines, the absolute amount of NORM can be greatest at points where workers access systems. These include where they remove filters and manually shake dust from them, and at locations to which ‘pigging’ machines have pushed scale and are accessed. We find levels of NORM in gas networks typically below 20 Bq/g, but have seen them as high as 200 Bq/g.
A regulatory approach to NORM
To place this in context with an example from just one jurisdiction with a relevant regulatory protocol, the UK considers materials with radiation levels of 5 Bq/g or more to be NORM. Various regulations are in place for the management, handling, storage, transportation and disposal of radioactive substances, including NORM, such as the Ionising Radiations Regulations 2017 (IRR)1, Radioactive Substances Act 1993, Environmental Permitting (England and Wales) Regulations 2016 and Transport Regulations (Carriage of Dangerous Goods) 2009. Though material with less than 5 Bq/g still has radioactive properties, it is out of scope of radioactive legislation.
Recent rule changes to the Environmental Permitting Regulations2 raised both the NORM radioactivity level and quantity above which sites need permits for handling and disposing of it, providing that certain conditions are adhered to. In the UK, most goes into landfill or is incinerated if levels of associated toxic materials including mercury do not exceed specified thresholds.
Management protocols for NORM
In DNV's experience, regulatory protocols are not always followed precisely and fully. In addition, training, personal protective equipment such as properly fitted face masks, and simple hygiene like washing hands before eating, can guard against breathing in or eating NORM.
DNV assists large gas network operators to develop management protocols for NORM. In our experience, some such operators are not as advanced in responding to the challenge. Awareness of NORM among industrial ‘off-takers’ from the gas system is very limited, in our view. These industries include power stations.
DNV supports analysis and handling of NORM
Drawing on years of historic and current data, our laboratory in Loughborough confirms that the NORM challenge is cropping up in more regions of the UK, for example. More operators are beginning to detect NORM and are asking how to measure, analyse and manage it. Our laboratory in Loughborough provides support, advice, and guidance on NORM to gas network operators. We conduct site audits of procedures, and check filters for NORM contamination and levels of risk. For example, we conduct these activities in association with a national public health authority to test radioactivity levels in samples of dust and sludge from pigging runs. We can also tailor services to your needs when it comes to handling, storage and disposal of NORM.
References
1 ‘Working with ionising radiation. Ionising Radiations Regulations 2017. Approved Code of Practice and guidance’, Health and Safety Executive, Series L121 (Second edition), March 2018, ISBN: 9780717666621
2 The Environmental Permitting (England and Wales) (Amendment) (No. 2) Regulations 2018
