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UK onshore gas pipelines – HSE safety update

11 January 2016

A recent report published by the HSE’s Hazardous Installations Directorate Gas & Pipelines Unit provides an update on the state of onshore gas pipelines in the UK, presenting a broad range of safety performance indicators (SPIs) from across Great Britain’s gas transmission, distribution and other hazardous pipelines sectors.  

Stock image
Stock image

The report - Major Hazard Safety Performance Indicators in Great Britain’s Onshore Gas and Pipelines Industry - Annual Report 2013/14 - is published annually in order to monitor the sector’s safety performance year-on-year.  

This annual report covers the period from 1 April 2013 to 31 March 2014 with the exception of data provided by National Grid Gas plc (NGG) for the National Transmission System (NTS) and pipeline data provided by the United Kingdom Onshore Pipeline Operators' Association (UKOPA), both of which cover the 2013 calendar year.

HSE Energy Division (ED) - Gas & Pipelines regulates health and safety in Great Britain’s gas and pipelines industry to ensure that risks at onshore major hazards sites, including pipelines, are properly controlled.  ED - Gas & Pipelines also works with ED - Offshore to regulate the safety of offshore installations and associated pipelines.  Gas & Pipelines contributes to Offshore’s programme of work by ensuring the integrity of: emergency shutdown valves; pig traps; risers; pressure protection systems; sub-sea  isolation valves; and wellhead pipework.

ED - Gas & Pipelines has worked together with the gas transmission, distribution and other hazardous pipelines sectors to identify a suite of SPIs and report performance against them. 


The main points for 2013/14 are as follows:

Third party damage: there has been a rise in the number of incidents in the two most serious categories of the United Kingdom Onshore Pipeline Operators' Association (UKOPA) infringement database.  The number of Gas Safety Management Regulations (GSMR) reportable incidents caused by third party damage has also increased substantially this year compared to last and is at its highest level since 2006/7.  Third party damage prevention remains a strategic priority for HSE.

Gas in buildings: this has dropped significantly and is at its lowest level since 1990/91; the five-year rolling average also shows a clear and sustained downward trend. 

Iron mains replacement: a new Enforcement Policy for the iron mains risk reduction programme came into force on 1 April 2013.  Under the new arrangements all of the Gas Distribution Networks (GDNs) now have eight year approval periods with the exception of Northern Gas Networks, who have a four year approval period.  HSE is monitoring year-on-year progress within these approval periods against indicative annual targets (IATs).  National Grid Gas fell short of their IAT for 2013/14, the other GDNs all exceeded theirs.

National Transmission System (NTS) gas quality: there was a sharp drop in the number of instances where transportation flow advice (TFA) was issued as part of the steps taken to manage the quality of gas entering the NTS. 

Public reported gas escapes requiring repair: more of these were dealt with by the GDNs this year compared to last, whilst the percentage prevented within 12 hours decreased.

GSMR reportable incidents: the overall annual total of GSMR reportable events showed a very slight increase compared to 2012/13.

Gas main or service failures: there were three events that met the relevant criteria, none of which resulted in fatal injury. 

This article will concentrate on the report’s findings in the first two categories – Third-party damage and Gas in buildings.

Great Britain’s Gas and Pipelines Industry 

Pipelines operated by the gas and pipelines industry in Great Britain transport natural gas and other hazardous substances around the country.  The sector also operates natural gas importation and storage facilities.  In Great Britain, approximately 22 000 km of pipelines are defined as Major Accident Hazard Pipelines (MAHPs) under the Pipelines Safety Regulations 1996 (PSR).  Of these, around 21 000 km transport natural gas at pressures above 7 barg and the remainder transport dangerous fluids such as ethylene.  In addition to MAHPs, the eight gas distribution networks (GDNs) also transport natural gas in pipelines operating at pressures below the MAHP threshold of 7 barg. 

Prior to 1 June 2005, Transco plc operated nearly all of the natural gas MAHPs in Great Britain and owned all eight of the GDNs.  After 1 June 2005, four of the GDNs were sold to: Southern Gas Networks plc; Scotland Gas Networks plc; Wales & West Utilities Ltd; and Northern Gas Networks Ltd respectively.  NGG retained four GDNs in London, the West Midlands, the East of England and the North West.  NGG also retained the NTS which delivers high pressure gas to each of the GDNs and other direct off-takes such as power stations.

Third-party damage: UKOPA Infringement Database

UK Pipeline Product Loss Incidents 1962 to 2013
UK Pipeline Product Loss Incidents 1962 to 2013

Third party infringements are one of the largest causes of transmission pipeline damage and failure in the UK and abroad.  The United Kingdom Onshore Pipeline Operators' Association (UKOPA) Infringement Working Group (IWG) collects data on infringements within the legal easement around a pipeline or in the pipeline operator’s declared zone of interest.  An infringement is any activity that either causes, or could have caused, damage to a pipeline or pipeline coating.  Examples of such activities include excavation, ditch digging, post-hole boring, directional drilling and levelling.

The UKOPA infringement database has been set up to identify trends in pipeline infringement and key factors leading to third party damage.  This intelligence allows targeted action to be taken to educate potential infringers and gauge the effectiveness of steps taken by pipeline operators to reduce the risk of infringements occurring. 

UKOPA have compiled an annual infringement report since 2004.  Initially only the chemical and oil sectors contributed to the infringement database, however its content increased significantly in 2005 with the addition of data from high-pressure natural gas pipeline operators.  Although not all of the data included in the database relates to MAHPs, all of the pipelines included have the potential to give rise to a major incident if ruptured.  UKOPA infringement reports are published on the UKOPA website:

UKOPA Infringement Risk Categories are as follows:

A: Pipeline Damage or Leak

B: Serious Potential for Damage

C: Limited Potential for Damage

1: Within the pipeline wayleave or easement.

2: Within the pipeline operator’s zone of interest, but outside the pipeline wayleave or easement.

Between 2009 and 2010 there was a significant fall in the number of infringements reported via the UKOPA database which is attributed to changes to the reporting arrangements for pipeline infringements.  For this reason no comparison should be drawn between infringement data from previous years and 2010, although data from 2010 onwards can be compared.

The 2013 data includes seven infringements in the highest 'A1' category out of a total of 764 recorded events.  These included:

*  two gas pipeline infringements associated with ditching activity;

*  an oil pipeline infringement during drainage installation;

*  a gas pipeline infringement during earthmoving operations;

* an oil pipeline infringement by an unknown party;

*  an oil pipeline infringement during work undertaken by a Local Authority.

There were also 78 category ‘B1’ infringements in 2013, the highest number since data recording changes were made in 2010.  Of the other infringement categories, C1 made the largest contribution to the number of recorded infringements.  This data emphasises the continuing threat presented by third party damage to pipelines and is strong justification for HSE’s focus on third party damage prevention as a strategic priority.

UKOPA Pipeline Product Loss Incidents Report

Annual reported GIB incidents from 2003/04
Annual reported GIB incidents from 2003/04

One of UKOPA’s objectives is to provide authoritative intelligence to inform risk assessments and aid decision making in the context of land use planning around high hazard pipelines.  To help meet this objective UKOPA has compiled a pipeline fault database which aims to: 

*  estimate leak and pipeline rupture frequencies for UK pipelines based directly on historical failure rate data for UK pipelines;

*  provide the means to estimate failure rates for UK pipelines for risk assessment purposes based on analysis of actual damage data for UK pipelines;

*  provide a more realistic and rigorous approach to pipeline design and routing; 

*  provide the means to test design intentions and determine the effect of engineering changes (e.g. to wall thickness of pipe, depth of cover, diameter, protection measures, inspection methods and frequencies, design factor etc.).

UKOPA define a product loss incident as:

*  an unintentional loss of product from the pipeline;

*  within the public domain and outside the fences of installations; 

*  excluding associated equipment (e.g. valves, compressors) or parts other than the pipeline itself.

The overall failure frequency over the period 1962 to 2013 is 0.223 incidents per 1000 km.year, a drop from 0.227 incidents per 1000 km.year for the period from 1962 to 2012.  The overall trend continues to show a reduction in failure frequency.  For the last 5 years the failure frequency is 0.105 incidents per 1000 km.year, down from 0.122 incidents per 1000 km.year covering the 5 year period up to the end of 2012.

The full UKOPA pipeline product loss and fault data report is published on the UKOPA website.

Gas in Buildings (GIB) Incidents

A GIB incident occurs when gas escaping from an outside gas main enters a building.  GIB incidents represent a significantly higher fire and explosion risk to members of the public than external gas escapes and are a strong indicator of the safety of the gas network.

A GIB event can only occur where leaking gas is able to enter a building.  This is why the GDNs give priority to decommissioning iron gas mains within 30m of occupied buildings.  They also prioritise their emergency response to deal with gas escapes with the potential to enter occupied buildings over those occurring a safe distance away. 

The graph below shows the annual number of GIB incidents reported since 2003/04, when data capture improvements were made.  The five-year ‘rolling’ average, which can show trends more clearly, is also shown. 

In 2013/14 the number of GIB incidents was 423, a substantial drop on 2012/13 and the lowest annual total since 1990/91.  The five year rolling GIB Incidents 5 yr rolling average since 2003/04 also shows a clear downward trend.  This suggests that the GDNs are securing performance improvements through risk-based prioritisation of both iron mains decommissioning and the repair of gas escapes near occupied buildings. 

The full report can be downloaded at:

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