managing risk and integrity of aging gas transmission pipeline · pdf filepipeline technology...

Pipeline Technology Conference 2007

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MANAGING RISK AND INTEGRITY OF AGING GAS TRANSMISSION PIPELINE

Arie Wisianto, Gas Transmission Dept PT PERTAMINA EP, Java Region

Abstract Extensive qualitative & quantitative risk assessment and followed by integrity assessment (ECDA, ICDA, SCCDA, mechanical integrity, geohazard study) have currently been performed on West Java Gas Pipeline- Indonesia. Almost 780 Km length of pipeline becomes a backbone that is transmitting natural gas collected from many resources in northern part of Western Java to Jabotabek until Cilegon heavy industry areas. Result from the assessment shows that under existing working pressure around 20 Ksc, the aging pipeline (25 years of age) generally still has a very high reliability and mechanical integrity. It is expected to have a long remaining life time (> 30 years). However the right of way is constantly facing third party damage threats since it consist of various populations, densities along pipeline routes associated with illegal occupation practices caused by recent heavy urbanization. To mitigate the risk and to manage the pipeline integrity associated with this potential third party damage, various practical solutions and recommendations are proposed so that the pipeline can safely be operated. Keywords: risk assessment, ECDA, ICDA, SCCDA, geohazard Introduction Gas Transmission Department (TG) is part of PT PERTAMINA EP Java Region, Its task dealing with gas transmission business in Java island (today operate gas transmission in West Java & East Java). Particularly in this paper we only discuss west Java gas pipeline network (figure 1). This business has been done since 1975 and today TG manage gas pipeline network around 13,588 In Km with various pipeline diameter from 4” – 32”, most of pipeline ( 69%) have more than 25 year of age ( figure 2). Currently TG transport natural gas around 480 MMSCFD to their customer in West Java, Banten and DKI province, operating pressure is varies from 175 psig - 420 psig. With existence of UU No. 22 concerning Oil and Gas year 2001, gas transmission and distribution business growth rapidly and it changes the nature of competition from natural monopoly into open market. For the agenda of fulfilling stake holder satisfaction, achieving high reliability of pipeline network is priority, but also doing expenses trade off in order to pursue optimum cost. How


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to do this activity into structured manner, easy to be controlled and well documented is through Pipeline Integrity Management (PIM) Program. Besides, TG EP Java Region also implements quality management system and environment management system, ISO 9001 and ISO 14000 certificates have been awarded. For the efficiency purpose PIM must be integrated into ISO 9001. PIM has been done based on ASME B31.8-S - 2001 as primary reference, and relevant technical references was utilized to support for example NACE, FIRE, ASME, DNV, CSA, ISO. Using PIM we can develop pipeline inspection, maintenance and repair (IMR) program as integrated and structured manner, in sequence and well documented. Pipeline Integrity Management Program PIM is a continuous improvement activity and must be supported by top management commitment, must be socialized and must be documented. PIM must be controlled from time to time because it is a life cycle process. Partner Selection Process TG want PIM program give added value to convince customer trust, therefore a high reputation and capability of contractor is required to assist our PIM program. TG requisite contractor shall have international successful experience of conducting PIM with regard of onshore pipeline, offshore pipeline and piping at station/plant. At the prequalification stage we got 11 participants but only 3 company pass technical and administration stage, TG develop high standard of criteria and specification because today PIM is a business commodity, many company who work related with pipeline usually offer PIM services but with different scope and definition. It is very important contractor who will perform PIM has capability and expertise inline with our requirement. Potential Threats and Data Gathering The first step of performing PIM is identifying potential threat and data gathering. ASME B 31.8-S categorizes pipeline potential threats into: - time dependent group - stable group - time independent group. Data gathering to be done with emphasize to data which have relationship with categories as mentioned above, some problems have been found when searching and collecting data for example data is stored into separate locations, missing data and unread data, data not complete, data managed by other department, communication gap or misunderstanding between team, data is not up to date, most data are come from hard copy and need extra time to read. Especially for offshore pipeline 24" from L Parigi – Cilamaya, only a view data can be obtained, so that engineering judgment and assumption must be done.


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Risk Assessment For the screening and risk mapping in order to develop priority/risk ranking of inspection, maintenance & repair (IMR), a qualitative risk assessment was performed after data gathering stage. This stage then followed by performing quantitative risk assessment (QRA) in certain places where having higher relative risk score. By QRA we can assess deeper to see how far is the risk? Is it acceptable or not comparing with standard or regulation? using QRA we are not only talking about relative risk as we get in qualitative risk assessment stage but we also get a number which can be plotted into acceptable area (ALARP) and define where we are today also where will we go after. Qualitative risk assessment was employed using a method developed by Kent W Muhlbauer, this qualitative risk assessment was applied to onshore pipeline (from pig launcher – pig receiver) and its result as depicted on figure 3. Risk based inspection (RBI) method was applied to piping station at gas compressor station (SKG Mundu, SKG KHT, SKG Cilamaya, SKG Tegalgede and SKG Bitung), RBI was conducted pursuant to API RP 581 and API RP 580 and its result as depicted on figure 4. QRA technique based on probabilistic and reliability method, QRA result can be represented into F (annual frequency of event with N or more fatalities) /N (number of fatalities) curve for societal risk, for individual risk can be represented into contour map. Offshore pipeline from L Parigi to Cilamaya was conducted in the same way. Pipe segment of Bojongraong to Sukaraja which often leak was analyzed using reliability technique, Weibull distribution function is employed to calculate its reliability and remaining life. QRA recommended Bojongraong – Sukaraja segment from Km 1 – 2.5 must be replaced. An example of QRA can be seen in figure 5. In some places QRA recommended to assess more detail and integrity assessment must be done furthermore. Integrity Assessment Following risk assessment, an integrity assessment must be done at several locations, realization of those recommendations are taken as follows: - Perform external corrosion direct assessment (ECDA), internal corrosion

direct assessment (ICDA) and Stress Corrosion Cracking Direct assessment (SCCDA)

- Perform geohazard study at location which are suspected having soil movement and erosion possibilities.

- Perform mechanical integrity assessment of rail and road crossing where traffic load is growth rapidly at certain location.

Mechanical Integrity assessment of rail and road crossing objective is to ensure pipeline line protection still sustain with its function to protect pipeline from


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external dynamic load & fatigue. Result of assessment can be seen on tables 2, from tables 2 it can be concluded that all rail and road crossing still under acceptance criteria, but at KP 74 and 75 segment pipeline 24” Tegalgede – Bitung it is recommended to install concrete slab as additional protection. Geohazard Assessment From Risk assessment result it was identified some places have potency of failure because of soil movement and erosion, following this finding a geohazard assessment was conducted (geotectonic hazard & hydro technique hazard study. From 15 locations which are suspected having of geohazard potential all have high plasticity clay (CH) classification except at Kali Unyur which is classified as low plasticity ( CL), but both of them are sensitive to erosion. Undercut slope and sheet erosion potential were identified at Cibeet river, Lemah Abang, Cicauh, Km 62.3, Ciasem river, Sentul Balaraja and Pasir Bulang. It is recommended to install additional protection at location which is susceptible to erosion while at place having sheet erosion potential can be solve by bio engineering technique, an example of geohazard assessment can be seen on figure 6. Internal of Corrosion Direct Assessment (ICDA) ICDA is usually performed to estimate internal corrosion rate for non piggable pipeline / segment. But in this study we did it also for piggable pipeline, combining data from intelligent pig and ICDA will enhance internal corrosion growth rate prediction. Using hydraulic transient simulation software (OLGA2000) fluid flow characteristic along pipeline can be modeled, hence internal corrosion rate and its location can be predicted. Data from simulation then validated and calibrated using direct examination (bell hole), and then if ILI data available internal corrosion growth rate will be estimated, if ILI data not available only data from simulation and direct examination will be used, an example of ICDA result is depicted on table 3 and figure 7. External Corrosion Direct Assessment (ECDA) There are of three choices method of integrity assessment, those are ILI, Hydrostatic testing and ECDA. ECDA is utilized at location where coating fault occurred and external corrosion is found. Direct examination using bell hole is to be done at the location and then corrosion size and its depth is measured and also it is needed to check how good is cathodic protection run within its design. In general the whole pipeline still under good condition, cathodic protection is running properly but there is stray current effect at certain location in Depok because of electrical influence from Jakarta – Depok train. An example of ECDA can be seen on figure 8.


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Remaining Strength and MAOP After all aspects of threats have been assessed and it seems so far so good, hence from operational perspective it is important to know how safe is the pipeline? Is it safe to be operated under MAOP as designed? Remaining strength calculation based on ASME B31.G and RSTRENGHT has been employed. Remaining strength assessment shows that pipeline still can be operated within its design safely, at certain location remaining strength located between MAOP and MOP based on ASME B31.G but based on RSTRENGHT criteria still above MAOP. Figure 9 show that ASME B31.G is more conservative comparing with RSTRENGRH. Remaining life In order to predict remaining life time, some methods have been used, NACE formula of remaining life assessment is RL = C.Sm.T / GR (C= calibration factor, SM = failure pressure ratio – MAOP ratio, t = wall thickness, GR = growth arte), this formula is widely used. But in some places a calculation based on reliability / probabilistic is required, and the result is depicted on figure 10. The result of remaining strength calculation shows that all pipeline still has remaining life time more than 30 years, but at Bojongraong - Sukaraja segment ( pipe 10" x 7 Km, KM 1 – 2.5) has remaining life = 0 and its mean strongly recommended to perform replacement program immediately. Inspection, Maintenance, Repair (IMR) Plan Some recommendation was proposed for 5 years IMR plan, risk mitigation also recommended at some places where risk is relatively high and according QRA its score located in ALARP region. Table 4 is an example of IMR recommendation. Conclusion

1. Pipeline Integrity Management facilitates top management to control, monitor, set up plan and develop IMR plan comprehensively.

2. PIM can present an answer qualitatively and quantitatively regarding its capability, reliability, particularly to the stake holder. Especially in this case of aging pipeline located around high population density.

3. In general, can be concluded that West Java main gas pipeline still safe to be operated within current condition, the average remaining life more than 30 years. But to ensure its reliability some risk mitigations still needed, and IMR as recommended must be followed accordingly.

4. Exception is made in case of Bojongraong - Sukaraja segment, it is recommended to perform replacement program immediately in Km 1 - 2.5.

5. lesson learned from experience shows that availability of complete data is very important to support PIM successful, because lack of data during PIM project an engineering judgment and assumption has been made, of


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course this situation reduce its accuracy but still acceptable as long as based on good engineering practice.

Acknowledgments The authors wish to thank the management of PT PERTAMINA EP for their permission to publish this paper, the authors are grateful to VP PERTAMINA EP Java Region and Manager of Gas Transmission Department for their support. References

1. Arie Wisianto, Satya A P “Evaluation of Risk Assessment Method, South Sumatera Gas Pipeline Case Study” Paper IPC2002-27004, ASME International Pipeline Conference, Alberta, Calgary 2002

2. Arie Wisianto, “Managing Integrity of Submarine Gas Pipeline Based On The Application of ASME B31.8-S” Paper IPC04-0413, ASME International Pipeline Conference, Alberta, Calgary 2004

3. Arie Wisianto, Harjana K “Strategi Implementasi Pipeline Integrity Management Untuk Jaringan Pipa Transmisi Gas Jawa Barat” Proceeding Indonesian Pipeline Technology 2004 Conference & Exhibition, Bandung January 2004

4. ASME B31.8-S, “Managing System Integrity of Gas Pipelines” ASME 2002 5. API 581,”Risk Based Inspection Base Resource Document”, API 2000 6. API RP 580, “Risk Based Inspection”, API 2002 7. PT Surveyor Indonesia, “Final Report Pipeline Integrity Management PT

PERTAMINA (PERSERO) DOH Jawa Bagian Barat’, March 2005


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Figure 1 Location Map

Figure 2 Pipeline age

Pipeline Age Distribution

0 - 5 yrs, 0, 0% 6 - 10 yrs, 1,317, 10%

11 - 15 yrs, 2,026, 15%

16 - 20 yrs, 468, 3%21 - 26 yrs, 415, 3%

27 - 30 yrs, 9,364, 69%

0 - 5 yrs 6 - 10 yrs 11 - 15 yrs 16 - 20 yrs 21 - 26 yrs 27 - 30 yrs

Diameter : 4",6",8",10",12",14",16"18",24",28",32"

Operating Pressure 175 - 420 psigTotal length 13,588 in-Km


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Figure 3 Qualitative Risk Assessment

Figure 4 Quantitative Risk Assessment

Figure 5 Risk based Inspection SKG Mundu


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Figure 6 Geohazard analysis (slope stability of Cileungsir river)

Figure 7 ICDA result

A transient hydraulic simulation by OLGA 2000 for ICDA

Contour

Inclination

Length (m)


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Figure 8 ECDA result

Figure 9 remaining strength assessment

Length Km


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Figure 10 Remaining life based on reliability method

Reliability vs Time Reliability

Time


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diameter Km point Relative

risk score

Integrity Assessment recommendation Remark

Cilamaya - KobakbiruKobakbiru 24" 36 38 3rd party damage -fatigue due to external loading at road crossing

37 38 3rd party damage -soil movement due to water erosion at Walahar

Kobakbiru - Serpong 24" 61 37 3rd party damage -soil movement due to water erosion at span bridge

67 27 3rd party damage

96 28.2 3rd party damage

99 25.1 3rd party damage corrosion


101 26.6 3rd party damage ROW fully accupied by illegal housing


103 27 3rd party damage

104 27.6 3rd party damage ROW fully accupied by illegal housing


106 25.6 3rd party damage corrosion -check mechanical integrity at rail crossing Depok

-check stray current possibility caused by train

118 24.9 3rd party damage corrosion

Serpong - Cilegon 24" 146 - 150 27 3rd party damage corrosion external corrosion at span bridge, coating fault

168 - 173 27 3rd party damage corrosion -check AC induced corrosion

191 26 3rd party damage corrosion High population density (at Pasar Rawuh)

Segment

SELECTED RELATIVE RISK RANKING (QUALITATIVE RISK ASSESSMENT)

Major Risk Contributor

Table 1

Table 2 Pipeline evaluation for external dynamic loading and potential failure


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Table 3 ICDA result

Table 4 IMR plan

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