Analysis and Comparison of Long-Distance Pipeline Failures

The analysis results of long-distance oil and gas pipeline failures are important for the industry and can be the basis of risk analysis, integrity assessment, and management improvement for pipeline operators. Through analysis and comparison of the statistical results of the United States, Europe, the UK, and PetroChina in pipeline failure frequencies, causes, consequences, similarities, and differences of pipeline management, focusing points and management effectiveness are given. Suggestions on long-distance pipeline safety technology and management in China are proposed.


Introduction
It is important to maintain high-pressure oil and gas pipeline systems safety and reliability, because the products are hazardous and may result in fire, explosion, and poisoning and lead to significant economic losses, casualties, and environmental pollution [1][2][3].By collecting and analyzing the failure data, pipeline operators can find out the causes of failure events and understand the weak point in pipeline management which is significant for pipeline risk identification, integrity assessment, risk mitigation, and accident prevention [4][5][6].
Statistical results of the US, Europe, the UK, and Petro-China in pipeline failure frequencies, causes, and consequences are comparatively analyzed.Similarities and differences of pipeline management are given.Suggestions on long-distance pipeline safety technology and management in China are proposed.

Analysis and Comparison
Failure statistical results of PHMSA in the US [7], EGIG in Europe [8], UKOPA in UK [9], and PNGPC in China on long-distance pipeline failure frequencies, causes, and consequences are comparatively analyzed.Table 1 shows the pipeline types that the analysis involves.

PHMSA.
Failure data of all pipelines in the US is updated to show the recent 20 years' statistical results and detailed information by PHMSA.Significant incidents of onshore pipelines (for liquid, only crude oil and refined and/or petroleum product are involved; for gas, only transmission line is involved) are filtered from the database and calculated for the failure frequencies in this paper.Significant incidents are those including any of the following conditions: (1) Fatality or injury requiring in-patient hospitalization.
(3) Highly volatile liquid releases of 5 barrels or more or other liquid releases of 50 barrels or more.
(4) Liquid releases resulting in an unintentional fire or explosion.
2.1.1.Failure Frequency.Figure 1 shows that from 2004 to 2015, failure frequencies of oil pipelines in the US vary between 0.4 times/kkm⋅yr and 0.6 times/kkm⋅yr, which is slightly increasing in the last 5 years as seen in the trend line.
As for the natural gas pipelines shown in Figure 2, the number goes up from 0.04 times/kkm⋅yr to 0.14 times/kkm⋅yr with vibration.3 and 4).Table 2 listed the causes and subcauses categorized by PHMSA.
(1) Corrosion.For liquid pipelines, corrosion is the most important factor for failure, while, for gas pipelines, corrosion is the top 3 of all failure factors.Among those, external corrosion usually accounted for more than 60%, mainly   (2) Pipe/Weld Material Failure.If the failure incidents for oil and gas pipelines are analyzed together, pipe/weld material failure is the top 1 factor.For subcauses that are analyzed, construction related (including field welded girth weld, backfill dent, etc.) accounts for more than 50%.
(3) Excavation Damage.Excavation damage is another important cause for oil and gas pipeline failures in the US, which accounts for 15% for oil pipeline failures and 22% for natural gas pipeline failures.Among those, the third party excavation damage accounts for the largest percentage, mainly due to the usage of one-call (excavation call system) system and the insufficient excavation practices.
(4) Natural Force Damage.In this cause, earth movement and heavy rain/flood are the main factors.
2.1.3.Failure Consequences.During 2004 to 2015, numbers of casualties and property loss caused by pipeline accidents in the US did not vary significantly, except the peak value in 2010 (see Figure 5), which is because of the rupture fire of the Pacific Gas and Electric Company's pipeline and rupture leakage of Enbridge 6B crude oil pipeline.The property loss includes estimated cost of public and nonoperator private property damage, product released intentionally or unintentionally, operator's property damage and repairs, operator's emergency response, and environmental remediation.

EGIG.
Up to 2013, the total length of EGIG gas pipeline becomes 144 kkm.The objective of EGIG is to collect and present data on loss of gas incidents in order to present the safety performance of the European gas transmission network to the general public and authorities.
The required criteria for an incident to be recorded in the EGIG database are the following: (1) The incident must lead to an unintentional gas release.
(2) The pipeline must fulfil the following conditions: (a) to be made of steel, (b) to be onshore, (c) to have a maximum operating pressure higher than 15 bar, (d) to be located outside the fences of the gas installations. Year

Failure Frequency.
From 1970 to 2013, the primary failure frequencies for the entire period (up to the year) per cause keep decreasing (See Figure 6).
In 2013, the primary failure frequency over the entire period (1970-2013) was equal to 0.33 per kkm⋅yr.This is slightly lower than the failure frequency of 0.35 per kkm⋅yr reported in the 8th EGIG report .The primary failure frequency over the last five years was equal to 0.16 per kkm⋅yr, showing an improved performance over recent years.

Failure
Causes.Top 3 causes for gas pipeline failures in EGIG are external interference, corrosion, and construction defects/material failure (see Figure 7).

Failure Consequences.
According to statistical results, in period of 1970-2013, only 5.0% of the gas releases recorded in the EGIG database ignited.Gas releases from large diameter pipelines at high pressure have ignited more frequently than smaller diameter pipelines at lower pressure (see Figure 8).
The highest fatality and injury rate can be found among the people who are directly involved in causing the incident.Eight cases (0.61%, total 1309) caused fatalities among the people causing the incident (see Figure 9).

UKOPA.
Up to 2014, the total length of UKOPA pipeline becomes 22.4 kkm.A product loss incident is defined in the context of this report as Frequency per 1000 km•yr (1) an unintentional loss of product from the pipeline, (2) within the public domain and outside the fences of installations, (3) excluding associated equipment (e.g., valves, compressors) or parts other than the pipeline itself.11).significantly decreasing as the manufacturing quality improved and the vintage pipelines abandoned.
(3) Construction Quality.This mainly includes girth weld defects, gouges, and dents.As the decreasing of illegal tap and manufacturing defects and also the well-controlled corrosion, construction quality becomes the top concerned factor in China now.
(4) Corrosion.As for the abandonment of old pipelines and all kinds of control methods, including periodic in-line inspection, corrosion is not as serious as before.However, pin-hole corrosions still cause failures, which are hardly detected by MFL.
(5) Third Party.This is mainly due to the supervision escaping, with unauthorized construction of third party, which causes damage on the pipes.As third party constructions mostly happen in the economically active regions, consequences are relatively serious.

Analysis Result Comparisons
Investigation and referring to foreign related failure statistics can provide good experience for domestic pipeline operators, while figuring out their own management level for continuous improvement.
3.1.Failure Frequencies.Compared with the failure frequencies (5 years' moving average) at home and abroad in the past 10 years, the value of PNGPC's oil pipelines is higher than that of the US, while that of PNGPC's gas pipeline is roughly at the same level compared to the US and slightly lower than the European (see Figures 15 and 16).

FatalitiesFigure 5 :
Figure 5: Failure consequences in the US reported by PHMSA.

Table 1 :
Mediums included in the statistical data.

Table 2 :
Causes and sub-cause categried by PHMSA.Locating Practices not Sufficient, One-call Notification Practices not Sufficient, One-call Notification Center Error, . . .Previous Damage due to Excavation Activity One-call Notification Practices not Sufficient, Previous Damage, . . .
galvanic corrosion, while internal corrosion is mainly of microbiological corrosion.
(1) Illegal Tap.With the enhancement of legislation, failure of this cause has a significant downward trend.(2)Manufacturing Defect.The majority of failures belonging to this cause are due to spiral weld defects, which is