Risk Assessment of Gas Pipeline using Risk based Inpection and

Fault Tree Analysis

M. Oky Zuhdi Alwan Lubis, Achmad Widodo, Gunawan Dwi Haryadi

Department of Mechanical Engineering, Universitas Diponegoro, Semarang, Indonesia

Keywords: Gas Pipeline, Assesment, Fault Tree Analysis

Abstract: During the operational period on the gas pipeline network there are many potential damage that can result in

pipeline failure. The pipeline operators need to perform risk analysis by identifying the damage,

determining probability parameters, the consequences of pipeline failures and performing risk calculations

so as to know the pipeline network risk profile and the impact for the people, the environment, assets, and

reputation of the company. More effective inspections can reduce the risk level by reducing the frequency of

future failures, through corrective and preventive action. In general, the purpose of this method is to screen

all equipment in an operating unit of a facility to identify areas of high risk, calculate the risk value of all

equipment in the operating unit of the product calculation of probability of failure and consequence of

failure, determine the priority of equipment requiring inspection based on the calculation of risk, develop an

appropriate and effective inspection program and manage the risk due to failure of an equipment and

determine the mitigation method to reduce the risk. This study aims to conduct risk assessment that can be

used further to minimize the failure that occurs in gas pipeline. The method used is risk-based inspection

(RBI) to plan risk-based inspections by comparing probabilities and consequences, arranged in a risk matrix

to obtain the level of risk. And the root cause of failure is investigated by using fault tree analysis (FTA)

method which to identify the causes of failure in depth, identify weaknesses in a system, assess and propose

for reliability or security, to identify the impact of human error, prioritize failure contributors, to identify

effective upgrades to the system, to gauge the probability of failure and to optimize the test and maintenance

so that the prevention solution can be found. Potential risks that cause the failure are congenital defects, less

routine maintenance, operating frequency, easy to dust, material age, difficult to reach the places and less

reliable operators. So the cause of the damage is human, equipment maintenance and environment.

1 INTRODUCTION

PT X is a gas transporter company which is a

consortium between a state-owned company and a

foreign company in operating distribution pipes in

DKI Jakarta area. The pipeline drains gas for

domestic industry needs. The onshore pipeline for

the domestic industry began operations in 1988. The

pipe which has a diameter of 16" is an API 5L-X52

pipe with a certain thickness that is adjusted to the

ROW (Right of Way) location class. During 14

years of the operational period there were many

potential damages which could result the failure of

pipeline. One of the pipe failure that occurred at the

end of 2010, the pipe has broken. A pipe rupture

occurs in one of the pipe segments located in Riau

area which results the supply of gas to an oil

company stopped. This incident became great

attention of the Indonesian government, because

with the rupture pipeline the national oil supply was

stalled which resulted in huge losses to the state,

pipeline operators company, or gas users.

The repair process that was carried out due to

the failure of pipeline caused the operation of the

pipeline and gas supply to consumers stopped for

several days. This has become the main concern of

management and the government to further improve

the integrity of the pipeline in pipeline operation. In

addition to the cessation of gas supply to customers,

failure in the gas pipeline transportation system,

both onshore and offshore, results in several risks

that endanger humans and the surrounding

environment in the event of a leak or explosion.

These failures can be caused by several factors,

including damage to the lining of the pipeline

(coating), duct pipe (denting), leakage (leaking),

Lubis, M., Widodo, A. and Haryadi, G.

Risk Assessment of Gas Pipeline using Risk based Inpection and Fault Tree Analysis.

DOI: 10.5220/0009006100430047

In Proceedings of the 7th Engineering International Conference on Education, Concept and Application on Green Technology (EIC 2018), pages 43-47

ISBN: 978-989-758-411-4

ruptured pipelines, or due to external interference

(third party activity) which can lead to pipe failure.

With that background, the application of risk

management and data / information management

that is applied in Risk Based Inspection (RBI) is

expected to be used as a system in developing

efficient and effective strategies in the operation of

pipelines to transport natural gas to customers.

Several studies and discussions have been

conducted to discuss risk management both in the

pipeline, platform and on systems that generally

have a high operational risk for gas companies.

Regarding the risk calculation method has been

discussed which presents an integrated quantitative

risk analysis method in the gas pipeline network

(Han Z.Y & Weng W.G, 2010). The method consists

of probability assessment, consequence analysis, and

accident risk evaluation. In addition comparative

risk assessments are carried out using qualitative and

quantitative methods. In the qualitative method,

index selection is based on statistical analysis of the

database of accidents that have occurred with the

calculation of weight according to the theory of

reliability engineering and the gray correlation

theory (Han Z.Y & Weng W.G, 2011) While the

quantitative risk assessment method, the possibility,

and consequences of different accidents are analyzed

and integrated.

The importance of pipelines that operate and

integrated well, a special strategy is needed so that

the pipeline network can operate properly and

safely. Risk analysis conducted in the RBI and also

the FTA discussed in this thesis is expected to help

pipe operators in determining the right method so

that the pipeline can operate properly and safely

through inspection, maintenance, and repair

activities (repairs if needed) which is carried out

regularly in accordance with certain rules and time

periods based on risk analysis (Tan Zhaoyang, Li

Jianfeng, Wu Zongzhi, 2011). In order for more

optimal implementation, it is necessary to integrate

well between the operating area of the pipe segment

with one another, whether from data, information, or

implementation schedule based on proper risk

priority analysis. The application of RBI and also

FTA can provide reliability and maintainability to

pipeline operations through proper inspection

strategies and maintenance procedures that can

minimize risks and provide added value and profit to

the pipe operator both in terms of availability and

pipe productivity..

This research was conducted to analyze the

risks in the gas pipeline. The field study was

conducted in one of the gas companies by collecting

data, measuring wall thickness on the gas pipeline

API 5L X-52 using a T-Gauge V, where the

measuring instrument has been calibrated. Data of

damage that has occurred previously was also

collected as supporting data. Preparing measurement

objects where there are 2 gas pipeline objects, GG

Macan - Citraland – Batas DKI line with a length of

7514 meters. Gas pipeline measurements are carried

out at the time of dismantling. Then the

measurement results data is collected, making a risk

assessment by calculating the probability of damage

and consequences of damage, identifying the cause

of the damage, then determining the appropriate

inspection step based on the results of the

calculation of the risk. The RBI method used in this

study is semi-quantitative based on the risk matrix.

And also the FTA method to find out the root cause

of the damage in detail. Once that is obtained, an

analysis process is carried out to get a careful

inspection plan recommendation.

2 METHODOLOGY

Pipeline Risk Management is one of the systems

used to regulate the strategy of a pipeline network

system by looking at the potential risks that exist so

that the pipeline system can still flow fluid to

customers according to the specified capacity

nomination (Kent M.W, 2004). Every pipeline

operator or company that has a pipeline does not

want a work accident (zero incident target) as long

as the pipeline operates. Conducting pipeline

integrity management by looking at potential risks is

the main objective and all pipeline operators. This

method continues to be developed sustainably by

and for pipe operators by providing the necessary

information and then implementing it in an

integrated manner through practical programs that

have proven effective in the oil and gas industry.

The practical program is conditioned and applies to

all pipelines both onshore and offshore, depending

on the information data available. This method has

been refined into 5 steps, and their detailed

explanation is given below.

Step 1: Hazard Identification. Pipe integrity is

mechanically determined by the type and size of

defects / defects or the presence of anomalies in the

pipe. Understanding the mechanism and behavior of

defects is very important to make the right plan to

reduce the level of pipe failure and improve the

safety of pipeline operations.

Step 2: Fault Tree Analysis. This method is

carried out with a top down approach, which begins

EIC 2018 - The 7th Engineering International Conference (EIC), Engineering International Conference on Education, Concept and

Application on Green Technology

with the failure or loss assumption of the top event

then details the causes of a top event until a root

cause failure (B. Vesely, 2002). FTA is a technique

to identify failures of a system. FTA is function

oriented or better known as "top down approach"

because this analysis starts from the top level and

passes it down. FTA is a technique for connecting

several series of events that produce another event

(Sunaryo, M. Aditya Hamka, 2017).

Step 3: Risk Analysis. The risk is the probability

of an event that can cause loss or failure or potential

failure. Whereas in general the danger is described

as a characteristic and a group that will cause

potential losses (Tan Zhaoyang, Li Jianfeng, Wu

Zongzhi, 2011) It is very important to make a

difference between danger and risk, because

basically risks can change without changing danger.

So the point is that risk can be reduced by

identifying and minimizing existing risks.

Step 4: Risk Based Inspection. Risk Based

Inspection is a method that uses levels risk as a basis

for prioritizing and regulating an inspection activity.

The potential advantage of this RBI method is that it

can increase the operating time and work of a

process facility where at the same time there is an

increase or at least maintenance at the same level of

risk (American Petroleum Institute, 2000) . The

purpose is to determine the possibility of an incident

occurring the probability and the impact of the

consequence also to identify defects or defects that

can cause large-scale accidents before they occur.

Step 5: Corrosion Rate Determination. Calcula-

tion of corrosion rate for pipes using API 570, the

formula for determining the corrosion rate is

determined by Eq. 1.

Corrosion rate =













(1)

Where : 



= thickness at current inspection

(inch)





= thickness on previous inspections

(inch)

The data needed to calculate the corrosion rate is

the thickness measured at previous inspections, the

thickness measured at the current inspection, and

age inspection (K. Elaya Perumal, 2014). This

corrosion rate serves to determine the remaining life

of pipe. The remaining life can be interpreted as the

tolerance of equipment to the type damage. This

remaining life will determine the interval time for

next inspection. The formula of remaining life is

determined by Eq. 2.

Remaining life =









(2)

Where : 



= thickness at current inspection

(inch)





= minimum thickness that should

be owned by the pipe

Step 6: Calculation of ar/t. Ar/t calculation

(damage factor parameter) functions in determining

factors thinning damage. Determination of ar/t is

obtained from time (a), corrosion rate (r), and also

thickness (t). This calculation is equivalent to the

fraction of the wall loss due to thinning. The formula

for a /t calculation is determined using the Eq. 3.s

ar/t =











3 RESULTS AND DISCUSSION

All data taken from PT. PGAS Solution in Jakarta.

PT. PGAS Solution provides limited data due to

classified confidential data from a company, so

Figure 1: Risk Based Inspection Process.

Risk Assessment of Gas Pipeline using Risk based Inpection and Fault Tree Analysis

based on the data obtained can use an analysis in the

form of semi-quantitative analysis. The type of

inspection carried out during inspection is in the

form of visual inspection. This visual inspection is

an external inspection that is inspecting from outside

of the pipeline. Because the results are in the form of

thickness data, this inspection uses a measuring

instrument, the T-Gauge V which is used to measure

the thickness of gas pipeline. Results of comparison

of each sample can be seen in Fig. 2 and Fig. 3.

Figure 2: WT vs Corrosion Allowance

Figure 3: WT vs Year Inpection.

The inspection interval carried out is every 300

meters where in each measurement 4 measurement

points are carried out every 90 degrees. Based on the

pipe installation process in 1998 with a pipe

thickness of 0.5, in 2018 showed a different average

pipe thickness. The average pipe thickness is 0.413.

The thickness of the pipe tends to decrease due to

thinning due to corrosion or commonly called

damage mechanism and also the thinning of material

FTA aims to identify the causes of failure in

depth, identify weaknesses in a system, assess and

propose for reliability or security, to identify the

impact of human error, prioritize failure

contributors, to identify effective upgrades to the

system, to gauge the probability of failure and to

optimize the test and maintenance. Failures that have

the highest risk level are analyzed to identify the

root causes of the problem based on the activity and

causes of other aspects that may be involved

Figure 5: Risk Matrix Analysis.

The analysis aims to reduce the possibility of a

risk where useful for controlling risk and minimizing

costs for controlling costs issued because of the risk

that might occur in the future. For effective

inspection and efficiently the inspection should be

based on the level of risk of the equipment.

0.05

0.1

0.15

300

900

1500

2100

2700

3300

3900

4500

5100

5700

6300

6900

7514

G‐ C‐ B

WTvsCorrosionAllowance

CorrosionAllowance(in) WT

0.448

0.446

0.438

0.426

0.413

0.38

0.4

0.42

0.44

0.46

2014 2015 2016 2017 2018

G‐ C‐ B

WTFinalvsInspection

WTFinal

Figure 4: Fault Tree Analysis.

EIC 2018 - The 7th Engineering International Conference (EIC), Engineering International Conference on Education, Concept and

Application on Green Technology

Based on the specified risk rating and also the

calculation of the remaining life an equipment can

be prepared an inspection plan. Frequency of an

inspection carried out no longer than half the

remaining period of use of the device. This matter

because if a piece of equipment has reached the

remaining half of its life, then the device has needed

more intensive attention and further analysis to

decide whether the equipment can still be used in the

operating system or not.

The effectiveness of each inspection carried out

within the time specified is characteristics for each

damage mechanism. The highest amount of

effectiveness will be used to determine the damage

factor. If several inspections are carried out and have

value low effectiveness over a specified time period.

An effective method is by referring to the visual

inspection and the addition of an analysis using an

ultrasonic device to measure the thickness of the

pipeline.

To determine the right inspection method is to

see the mechanism of damage that occurs. In this

analysis, the damage in the form of thinning, namely

thinning of the wall thickness due to localized

corrosion.

Some methods that can be used are visual

examination, ultrasonic straight beam, eddy current,

flux leakage, radiography and dimensional

measurement. These methods are the most effective

method used for this type of thinning damage. Not

all of the above methods are used in their

application, this involves costs if all methods are

used.

4 CONCLUSION

Gas pipelines are one of the most potentially high-

risk job sites that can cause workplace accidents to

minimize the possibility of damage occurring using

the RBI method and the Fault Tree Analysis method.

RBI to plan risk-based inspections by comparing

probabilities and consequences, arranged in a risk

matrix to obtain the level of risk. And the root cause

of failure is investigated by using FTA failure

analysis diagram method.

Potential risks that cause the failure of congenital

defects, less routine maintenance, operating

frequency, easy to dust, material age, difficult to

reach places and less reliable operators. Hazard

identification was used to identify the hazards that

have highest risk level, and FTA was used to search

for the root causes of those hazards

ACKNOWLEGMENT

The author would like to express the gratitude for

the management of PGAS Solution for their kind

contributions in providing invaluable data and

information, and for granting permission to conduct

survey and site visits, so that the study could be

carried out successfully. This study was supported

by Department of Mechanical Engineering,

Diponegoro Unversity.

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Risk Assessment of Gas Pipeline using Risk based Inpection and Fault Tree Analysis