Pipeline Gas Detection

8/8/2019 Pipeline Gas Detection

1/12

Rangkuman Diskusi Mailing List Migas Indonesia BulanNovember 2006

Pipeline Gas Detection

Anpan

Saya mau tanya dimana saya bisa menghubungi Company yangberpengalaman untuk mendeteksi Pipa yang bocor di Onshore atauOffshore. Kalau boleh dengan alamat detailnya agar saya bisa langsungcontact mereka.Salam dan terima kasih,

Nugroho Wibisono

Pak Anpan,

Kalau dikumpeni kami ada perangkat lunak yg memang dipasang khusus untukmendeteksi kebocoran pipa yg perhitungannya didasarkan pada prinsip massbalance dan pressure balance. Hasil kalkulasi perangkat lunak dan hasil pengukurandilapangan dibandingkan, jika deviasinya terlalu besar, maka sudah patut untukdicurigai. Keakurasiannya cukup tinggi dan juga sudah terbukti dilapangan. Jadi tidakperlu cari perusahaan yg khusus nyariin kebocorannya terletak dimana karenaaktivitas pencarian ini saja sudah makan waktu, belum lagi penanganankebocorannya, harus mobilisasi tim lain lagi yg sudah harus siap dengan diver, ROV-nya beserta peralatan yang sesuai dengan sebab kebocorannya (kalau yg terakhir ini

bukan urusan saya, jadi saya ga terlalu ngerti juga sih hehe).Mengomentari pak Roeddy, sepertinya tidak se-piece of cake itu di offshore.Kalau pipeline anda ratusan kilometer disubsea, sepertinya tidak akan mudah juganyari bocornya kalau pakai perahu ya. Pipeline sepanjang itu kalau lagi kempes2nyakarena bocor juga tidak akan cepat pulih jumlah linepack-nya meskipun sudahdigenjot produksi gas ratusan mmscfd. Beda urusannya kalau yg dibicarakan pakRoeddy itu ternyata untuk pipeline yg di intra field yg panjangnya mungkin hanyapuluhan kilometer atau bahkan dibawah 10 km.

Mungkin itu dulu dari saya, silahkan dikoreksi kalau ada kesalahan.Thanks.

roeddy setiawan

Dear Pak Anpan,Wah wah serious banget ini info nya, anyway kalau di onshore yang buried ini repotsekali banyak issue.a. gas yang bocor umumnya travel ke least resistant path, misalnya actual leak nyadi Km 01, tapi bisa dia keluar di Km02. karena gas nya keluar menyusuri pipa dankebetulan di km02 ada rekahan jadi dia keluar disitu padahal kan jauh dr tempatbocor, begitu digali ngak ketemu.b. liability company ke lingkungan nya besar banget


2/12

Umumnya perusahaan gas di amrik secara periodik melakukan integrity test,berdasarkan data dari pipa tersebut (hasil overline survey, hasil IP, corrosionmonitoring, kembang kempis nya pipa saat operasi) dr sini mereka akan membuatassesment apakah pipa di derating atau di keep seperti semula.balik ke pertayaan bapak, terus terang saya belum pernah tahu ada company yanghusus nyarikan kebocoran buat kita. yang biasa kita lakukan dr saat design adalah

memasang "mass meter" di sender and receiver. lalu kita bikinkan base line yangacceptable, ini berdasarkan neraca massa yang transient, differences antarasending and receiving harus ada di range tertentu (kira kira cocok dg dv/dt dr teory).saya dengar sekarang OLGA punya software yang namanya predict tapi terus terangsaya tidak tahu hasilnya.tapi kalau memang ada dugaan kuat bocor, saya kira di kasih odorant saja terusanak buah anda di suruh survey overline pake chromathograph alami ini, at least,mereka akan menemukan kira kira tempatnya. cara lain yang biasa dipakai adalahmemakai tubing dan small manual drill, di bor sampai kedalaman timbunan pipa,terus dihisap dg vakuum pump dan di umpankan ke gas monitor atau HPcromatograph yang portable.kalau di offshore piece of cake. dari map side scan survey, anda tinggal overline

survey saja pakai perahu, nanti ketemu. sudah ketemu kira kira nya baru jump diveruntuk memastikan, drop buoy. tinggal kasih ke construction buat pasang clamp.kalau ngak ketemu company yang nyariin kebocoran, anda bisa contact pt setiawan(he he joking) pak.

roeddy setiawan

Dear Pak Nugroho,

interesting pak perangkat lunak yang terpasang ditempat anda. bisa di share pakbagai mana alat tersebut bisa menentukan titik lokasi kebocoran berdasarkanmaterial ballance, kalau bisa di attach via pak Budhi theoritical basis nya biar kitasemua bisa belajar sekaligus study kasus dimana kebocoran ketemu berdasarkan

perangkat lunak tersebut. ini kan make our life easy

Kalau jaman dulu, yang saya kerjakan umumnya di pressurize, jump diver atau ROVcuman lihat buble. ngak ketemu di kasih dyes plus ROV, ngak Ketemu ROV nyadikasih sensor yang pick up acustic signature dr pipeline. terahir kalau ngak ketemuterus di kasih short life radioactive tracer, sambil di run rov dg sensor nya. biasanyasebelum ke tracer sudah ketemu. proses iterative ini bisa lama mana sambil dipendelikin pak superintendent, pak operation mgr, sampai pak VP, its not niceexperience ha ha ha (joking)

Dicky

Pak Roeddy,Barusan saya ikut presentasi software "pipeline studio', punyanya energy solutions.Saya kurang memahaminya krn saya bukan orang proses.Sepertinya software ini punya kemampuan untuk menganalisa leak di pipeline.Bisa steady state analysis (offline) dan transient analysis (online)

Kalo gak salah, pgn dah make cukup lama (cmiiw).

Bisa dilihat di: http://www.energy-solutions.com

roeddy setiawan
http://www.energy-solutions.com/http://www.energy-solutions.com/


3/12

Dear Pak Dicky,

Wah sayang saya ngak bisa ikutan lihat presentasi mereka, memang kalaumenetukan pipanya bocor pakai neraca material biasa kita tahu.

misalnya kalau di offline kan didekati dengan neraca material steady state, jumlahmasa setiap saat yang dipipa (dm/dt) , tidak ada mass in, tapi ada mass out, jadipenurunan tekanan sebanding dengan kebocoran. untuk online in prinsip sama jugatapi saya kira proses nya transient.

tetapi untuk menetukan coordinat dimana lokasi kebocorannya, sehingga kita bisadatang ke lokasi yang ditentukan untuk melakukan remedial work. saya engak tahubasic theoritical nya . kalau ada rekan millis yang tahu please share.

Budhi, Swastioko (Singgar Mulia)

LEAK DETECTION TECHNIQUES

GENERALLeak detection techniques are based on either continuous or intermittentmeasurements of specific parameters. Intermittent leak detection methods are oftenable to detect smaller leak rates compared with continuous leak detectiontechniques.Some continuous techniques can only detect transient pipeline conditions during theonset of a leak, and will not be able to identify the presence of a leak at a later time.

For some intermittent techniques fluid transportation through the pipeline needs tobe interrupted. Using intermittent techniques, the detection time of a leak will becompletely dependent on the frequency of inspection.

Techniques for detection of leaks in liquid lines offer better performance than thosefor gas pipelines, which in turn are better than those for two-phase pipelines.

The conflicting balance of sensitivity to leaks and false alarms will determine thesensitivity setting of the leak detection system. Large leaks can normally be detectedmore rapidly than small ones. To maintain the user's confidence in the system,avoiding false alarms should have a higher priority than attempting to shorten theleak detection time or reducing the minimum detectable leak rate.

The performance of pipeline leak detection techniques is dependent on fluid type,operating pressure including fluctuations, batch or continuous operation, pipelinelength and size, metering accuracy, etc.

To decide which technique to adopt depends on a detailed case by case evaluation. Ifthe consequences of a leak are considered significant then the more sophisticatedtechniques of leak detection are required. It may be necessary to deploy more thanone leak detection technique in order to achieve the overall leak detectionperformance that is required.

Leak detection systems are categorised into the following groups according to theirinherent principle of leak detection:

1. Balancing of pipeline mass input versus output


4/12

2. Pressure and/or flow analysis3. Monitoring of characteristic signals generated by a leak4. Off-line leak detection

A summary of the capabilities and application of the various leak detectiontechniques is given in Table 1.

1. BALANCING OF MASS INPUT VERSUS OUTPUTThis category of leak detection systems relies on the fact that in a leak-free pipelinethe fluid mass flow into the pipeline equals the flow out. Using this mass balanceprinciple the flow-in and flow-out measurements are continuously monitored for anyvariations over a time interval. Volume flow readings should either be corrected fordensity or pressure and temperature variations to reference mass flows. To eliminatethe effect of flow variations during normal operation, the flow readings should beaveraged (totalised) over discrete time periods.

The uncorrected mass balance method can be applied only under steady stateoperations as it does not allow for changes in the pipeline inventory, i.e. line packvariation. Its accuracy depends largely on the accuracy of the flowmeters and on thesteadiness of operations.

In addition to the inlet and outlet flow measurements, the corrected mass balancemethod uses a correction factor for any changes in the pipeline inventory. Pressureand, if necessary, temperature measurements at intervals along the pipeline areused for calculating the correction factor. The capability for detecting small leaksdepends upon the number and accuracy of measurements along the length of thepipeline.

An alternative method is dynamic simulation, which is a model-assisted balancemethod. A real time computer model calculates the inventory of the pipeline and theline pack variations of the pipeline under steady-state and transient operatingconditions. It will correct not only for pressure and temperature effects but also forchanges in fluid properties, such as where different batches of fluids are present inthe pipeline at the same time. A difference between the mass balance predicted bythe model and that actually measured indicates the presence of a leak. Also,unexpected flow and/or pressure trends are used as indicators of the occurrence of aleak.

The dynamic simulation method is similar to the corrected mass balance system. Themain difference is that the dynamic simulation method calculates the pipelineinventory whereas the corrected mass balance method interpolates between themeasurements along the pipeline. The latter is usually considered to be less accuratebecause of the inherent accumulation of measurement errors.

The sensitivity of these methods is generally good. Their disadvantage is that theyhave limited capabilities for locating the leak.

Shell Research (KSLA) have developed a statistical pipeline leak detection (SPLD)system. The system does not need complicated modelling of the pipeline inventory, itcontinuously calculates the statistical probabilities of a leak based on fluid flow andpressure measured at the inlet and outlet of a pipeline. Depending on the control andoperation of a pipeline, the statistical technique is used to identify changes in therelationship between the pipeline pressure and flow which always occur when thereis a leak. The SPLD system works as a statistical filter, which is applied to a pipelineinput/output balance and which decides between a leak-free and a leak-present


5/12

hypothesis. Major advantages of this system are its simplicity and robustnesscompared with other software based techniques. The SPLD system can run on a PC,and is capable of discriminating between fluctuations due to operational variations ofthe pipeline and the actual occurrence of a leak; it is thus very reliable for leakdetection. The SPLD system can only give an indication of the leak location. The SPLDsystem has been commercialised since October 1991. The statistical filter of the

SPLD system can also be combined with a commercially available dynamic simulationmethod, which makes the latter even more reliable. This combined statistical anddynamic simulation leak detection system is at present the most sophisticated leakdetection system available.

2. PRESSURE AND/OR FLOW ANALYSISThe operation of a pipeline can be characterised by the flow of the fluid and thepressure gradient along the pipeline. Pressure drop and flow along a pipeline arerelated to the flow resistance of the pipeline. A leak will alter the pressure dropprofile of a pipeline and therefore affect the 'normal' pressure and flow relationships.Detection of such alterations can be used to indicate the occurrence of a leak.

If a large leak occurs, particularly in the upstream part of a pipeline, the inletpressure will drop. Observation of a lower than expected inlet pressure indicates thepresence of a leak. Detection of low pressure is usually connected to an automaticshut-down system. To avoid false alarms the system is usually set such that onlymajor leaks can be detected.

A leak will result in an increase in flow upstream and a decrease in flow downstreamof the leak. As a result of this the pressure gradient will increase upstream anddecrease downstream of the leak. The occurrence of a discontinuity in the pressuregradient, which is calculated from the pressure readings along the pipeline, is anindication of a large leak. The rate of change of pressure and flow readings can alsobe monitored and used to detect sudden changes which indicate the occurrence of aleak.

The combined pressure decrease/flow increase method uses the fact that a leak in anoperational pipeline will cause an increase in the flow and a decrease in the pressureupstream of the leak. The simultaneous occurrence of both is an indication of a leak.

3. MONITORING OF CHARACTERISTIC SIGNALS GENERATED BY A LEAKA suddenly occurring leak will cause a sudden pressure drop at the leak location inthe pipeline. This sudden pressure drop will create a pressure wave travelling atsonic velocity both upstream and downstream from the leak. Detection of thispressure wave is an indication of the occurrence of a leak. The response time of thisnegative pressure wave technique is very short because it responds to waves thattravel at sonic velocities (in crude oil, approximately 1000 m/s). When the wave isdetected both upstream and downstream of the leak, the location of the leak may becalculated from the time difference of detection by the nearest sensors on either sideof the leak location. The system will only respond to an instantaneously occurring

leak of measurable size. In practice the sensitivity can be poor because the alarmthresholds are often set high to avoid false alarms triggered by pressure transientsgenerated by upstream or downstream processing plant or other noise producinginstallations, such as pump or compressor stations.

A system which is less sensitive to pipeline noise than the negative pressure wavesystem uses dual transducers which filter out noise signals. The system is madedirectional, i.e. it detects signals originating from either the upstream or thedownstream direction of the pipeline. This is achieved by installing the two


6/12

transducers at an appropriate distance from each other and using an electronicsignal subtracting system.

Leak detection based on negative pressure wave techniques will only detect theinitiation of a leak and not its presence. If the pressure wave created at the momentof leak initiation is not detected, the leak will not be noticed.

Liquid escaping under pressure through a small opening produces supersonic noise.An ultrasonic leak detection pig, which is equipped with hydrophones and datarecording, can detect and locate the presence of a leak. A very small leak, down to10 l/hr, can be detected and fairly accurately located with this technique. Beingintermittently operated, the response time will depend on the frequency of runningthe ultrasonic leak detection pig.

A hydrocarbon-permeable tube (sniffer tube) can be laid in close proximity along thepipeline. Small leaks of hydrocarbons from the pipeline which have permeated intothe tube will be detected when the tube is periodically purged into a gas analyser.

Hydrocarbon-sensing cables can be laid along the pipeline. Electrical properties ofthe cable change when hydrocarbons come in contact with the cable. Contact withwater does not affect the properties of the cable.

A prototype system for the measurement of methane in sea water has beendeveloped. The device, which is mounted on a ROV, extracts dissolved gas from acontinuous flow of water and determines the methane content using infraredabsorption techniques.

Remote sensing of hydrocarbon emissions, e.g. using an infrared technique from anaircraft is becoming commercially available. Particularly for gas and multi-phasepipelines, this offers a powerful alternative to ground based patrolling techniques.

4. OFF-LINE LEAK DETECTIONIntelligent pigs have been developed for detection and location of leaks in a pipelineusing flow direction recognition in a blocked-in pressurised pipeline. This bi-directional pig has an opening through the body with a sensitive flow meter and atransmitter. By locating the pig at various points along the line and using above-ground interpretation of the flow measurements through the pig, the leak caneventually be located. Locating the leak, however, is time consuming and the lineshould be equipped with pumping or pressurising facilities at both ends. This systemis of interest for pipelines larger than 8 inches in diameter when a small leak hasbeen detected but its location is unknown.

An alternative to the above technique for pipelines smaller than 8 inches is a bi-directional pig equipped with a differential pressure transducer and a transmitter.When located in the pipeline the pig measures the pressure drop on either side. Theleak will be on the side at which the pressure drops more rapidly.

The pressure in a blocked-in pressurised pipeline will drop when there is a leak. For astatic pressure leak test the pipeline, or a section of it, is pressurised with thetransported hydrocarbon fluid to the MAOP. If pressurising to a higher level isrequired the leak test shall be done with water for safety and environmental reasons.After pressurising, the block valves are closed and the pressure and temperature aremonitored for a specified period of time (24 hour minimum). A differential staticpressure test can be carried out if block valves are equipped with differentialpressure transducers. A difference in the rate of pressure drop in two adjacent


7/12

sections that cannot be explained by temperature effects, inaccuracy of readings orvalve leakage is an indication of a leak.

There are uncertainties about the advantages and disadvantages of pressure testingexisting pipelines for condition monitoring purposes at pressures higher than theMAOP. Pressure testing above the MAOP is primarily done for strength testing in

order to avoid a pipeline rupture. The advantage of pressure testing at highpressures for leak detection is that an existing leak is detected more easily. Also,long defects which have almost broken the surface can be opened, resulting in a leakwhich is also detected. The disadvantage is the risk that existing defects might beenlarged and/or activated to grow, possibly leading to failures during normal pipelineoperations following the pressure test.

A tracer can be added to the pressurising fluid for detection of small leaks. The leakis detected by patrolling the pipeline with a detector which is sensitive to the traceror by visual observation of a visible tracer.

Sound which is generated when liquid is forced through a small opening duringpressure testing can be detected by acoustic monitoring. For pipelines transportinghard liquids, leak detection by an acoustic reflectometry method is feasible. Thetechnique is based on the phenomenon that a pressure wave travelling through apipeline is reflected at the position of a leak, due to a local change of acousticproperties. For lines which are used intermittently this technique can be used duringdowntime when the level of disturbing noise is low.

TABLE 1 SUMMARY OF THE CAPABILITIES AND APPLICATION OF LEAK DETECTIONTECHNIQUES

leak detection methodleak typemode of operationresponse timeleak location capabilityremarks

low pressuregas: full bore ruptures liquid: major leaksanyseconds to minutesOffshore: None

Onshore: Between block valves if pressure readings availablecommonly used, high thresholds to avoid false alarms

pressure decrease / flow increase

gas: major leak liquid: large leakssteady stateseconds to minutesOffshore: None

Onshore: Between block valves if pressure readings available

pressure gradient along the pipeline


8/12

gas: major leaks liquid: large leakssteady stateminutesbetween block valves if pressure readings availableonshore only

negative pressure wavegas: large leaks liquid: medium leakssteady stateseconds to minuteswithin 1 kmdetects only the onset of a leak

wave alertgas: medium to large leaks liquid: small to medium leakssteady and transient stateseconds to minuteswithin 1 km, depending on transducer spacingdetects only the onset of a leak

mass balancemedium to large leakssteady stateminutes to hoursnone

corrected mass balancesmall to medium leakssteady and transient stateminutes to hoursOffshore: None

Onshore: Between block valves

dynamic simulationsmall leakssteady and transient stateminutes to hoursat best within 10% of pipeline length

statistical leak detectionsmall leakssteady and transient state

minutes to hoursindication onlylow probability of false alarm

ultrasonic leak detection pigliquids: small leaks (typical 50 l/h)intermittentdepends on pigging frequencywithin 100 m


9/12

hard liquids onlyacoustic reflectometryliquids: large leaks (on-line), small to medium leaks (shut-down)steady statedepends on monitoring frequency

within 1 kmhard liquids onlydifferential static pressure testsmall leaks (hard liquids), medium leaks(soft liquids), large leaks for gasduring shut downhours to daysnone, between block valvescapabilities depends on length and temperature effects

sniffer tube, hydrocarbon sensing-cablesall fluids, including multiphase: small leaksanyhourswithin 100mshort lines only

Leak rate categories used in Table 1:

Full bore rupture: 100% of flow

Major leak:50-100% of flow

Large leak:25-50% of flow

Medium leak:5-25% of flow

Small leak:1-5% of flow

Nugroho Wibisono

Pak Roeddy,

Kurang lebih prinsip kerja dari perangkat lunak yg ada dikumpeni saya itu sepertipada artikel pak Budhi. Memang selain indikasi dari perangkat lunak, kita jugamemonitor kondisi pressure pada pipeline secara manual. Cuma tetap saja, kalaubocornya halus, lama juga ketahuannya pak, kalau pipeline-nya pendek sih kayaknyabisa lebih cepet ketahuan. Hal lain yang harus diwaspadai juga kualitas dari datayang diterima oleh perangkat lunak tersebut. Biasa lah, garbage-in garbage-out,terima data jelek, hancur lah hasilnya.Semoga membantu.


10/12

roeddy setiawan

Dear pak Weby,

Terimakasih atas info nya. Yang saya belum faham. dari software tersebut, bagai

mana menentukan lokasi kebocorannya, say di koordinat km 10.2 misalnya.karena kalau dari data material ballance, pressure calculation dan theory mechanicdr fluid flow. dengan hanya punya data kedua ujung pipa sepertinya hanyamenentukan yes pipa nya bocor, tapi letaknya dimana tetap saja harus pakeinvestigative tooll, misalnya ultrasonic pig dikombinasi dengan magnetic marker.saya tertarik sekali kalau pak webi bisa menjelaskan lebih detail kalau memungkinkan.

"Swastioko, Budhi"

Kebetulan saya baru saja meng-upload dokumen Pipeline Leak Detection Study(1514 KB) yang dilakukan oleh Bechtel. Dokumen tersebut dapat didownload dari

URL http://www.migas-indonesia.com/index.php?module=download&act=go&id=14.Pagi ini saya lihat sudah 37 orang yang mendownloadnya. Isinya bagus lho karename-review semua teknologi pendeteksian kebocoran pada pipeline, diantaranya :

> 1. Mass Balance> 2. Rate of Change> 3. Pressure Point Analysis> 4. Wave Alert> 5. SCADA-based Systems> 6. Acoustic Emission Systems> 7. Chemical Based Systems> 8. Temperature Profile> 9. Fibre Optic Sensing Technologies

> 10. Neural Networks> 11. Radioactive Tracings> 12. Intelligent Pigging> 13. Miscellaneous MethodsMasing-masing metoda mempunyai keuntungan dan kerugian.

Budhi S.

First of all, mohon buntut email dihapus dulu sebelum me-reply, save bandwidth !.Kelihatannya Pak Rudy masih penasaran terus dengan bagaimana cara kerjanyadalam menentukan letak kebocoran.Dulu saya pernah mengevaluasi satu produk, dan ternyata tekniknya dengan

menggunakan Pressure Point Analysis.Dan untuk menambah akurasi pendeteksian kebocoran, perlu juga ditambahkanflowmeter dengan metoda Mass Balance.Dan hebatnya, caranya cukup simple yaitu dengan memasang Pressure Transmitterdi kedua ujung pipa. Tentu ada batasan panjang pipeline agar tidak menimbulkanfalse error, rasanya sih 30 km.

Teorinya simple yaitu dengan mendeteksi adanya shock wave yang merambatsepanjang pipa dari titik kebocoran.


11/12

Yang kompleks adalah algorithma pendeteksian, nah ini yang disimpan rapih olehmereka, tidak bisa diketahui oleh umum. Menurut keterangan penjual, perludilakukan tuning yang lama selama instalasi untuk mengeliminasi false alarm.

Kalau mau tahu lebih detail, ada suatu study yang dilakukan oleh Bechtel (lihat arsipmilis dibawah pada tanggal 20 feb 2004).

Sayang dokumen hasil scanning ini berukuran sekitar 1.5 MB, jadi tidak bisa masukmilis.Silahkan anda download di situs Migas Indonesia Online, mudah-mudahan belumdihapus oleh administrator.Kalau sudah dihapus, bisa saya kirimkan via japri ke anda.

Tapi sesudahnya, anda mengirimkan kembali ke anggota milis yang membutuhkan.

roeddy setiawan

Dear Pak Budhi,

Terimakasih atas tambahan penjelasan nya, I got the point. saya kira shock wavemerambat ke dua arah, travel time nya berbeda, dari sini dihitung coordinate nya,lalu di cross check dengan material ballance.

somehow pendapat saya metoda ini hanya punya satu kali kesempatan saja yah pakBudhi ?, sekali meletus sudah tidak akan ada lagi yang kedua atau ketiga (karenashock wave nya hanya ada satu). tapi saya yakin company ini sudah punya data basemacam2 shock wave di alatnya, jadi tinggal mencocokan signature nya. tidakdikacau kan oleh shock wave dr pig yang baru di launching, atau pig yang stop andgo selama perjalanan.

Budhi, Swastioko (Singgar Mulia)

Yeah... You've got the point. Tapi bisa saja sih kalau kebocorannya bertambah besar,kan akan menimbulkan shock wave kembali. Makanya saya perhatikan, vendor

membutuhkan waktu yang lama untuk men-set up peralatan untuk disesuaikandengan operasional pipeline yang dimonitor.Mungkin untuk membuat database dari trend operasi sehari-hari.

Feeling saya sih, metoda PPA lebih baik dikombinasikan dengan metoda nyanglainnya. Nah beberapa teknologi yang ada itu sudah dikaji oleh Bechtel. Dokumenberukuran 1.5 MB ini sudah saya kirimkan ke anda via japri, jadi bagi anggota milisyang berminat, coba rayu Pak Rudi untuk mengirimkannya ke mailbox anda.

Nugroho Wibisono

Pak Roeddy,

Saya pikir untuk kebocoran pipeline adalah kasus per kasus. Untuk yg kasusmendeteksi shockwave karena ada bursting pada pipanya, ya mungkin hanya satukali saja kita punya kesempatan untuk mendeteksi kebocoran tsb, kalau lewat, yawassalam saja. Saya ragu, apakah ini dapat diaplikasikan pada pipeline yg sangatpanjang? Apakah gelombang kejut ini bukannya akan semakin teredam dengansemakin panjangnya medium perambatannya? Sehingga ketika sampai diujung pipa,si pressure transmitter-nya hanya mendeteksi energi yg kecil saja dari gelombangkejut, dan hal tsb bisa saja diartikan sebagai noise.


12/12

Supaya lebih tegar (robust), mustinya memang metode PPA (pressure point analysis)ini tidak berdiri sendiri dan dikonfirmasi oleh perhitungan lain, seperti mass balance.

Jadi penentu kebocoran tidak hanya berdasarkan variabel tekanan saja. Lebih baikrepot verifikasi diawal (sebelum mobilisasi tim lapangan ke lokasi kebocoran),daripada repot diakhir (dimarahin bos karena menghambur2kan duit ngirim timlapangan untuk nyari kebocoran bohongan hehehe).

Mengomentari lamanya waktu untuk set-up yg dipaparkan pak Budhi. Mungkinlamanya waktu ini untuk memverifikasi hasil kalkulasi oleh model yg sudahembedded didalam sistem buatan mereka dibandingkan dengan kondisi riilnya.Kemudian mereka bisa saja mengubah beberapa besaran didalamnya supaya cocokdengan kondisi lapangan dalam keadaan normalnya. Setahu saya, yang namanyapemodelan sistem (apalagi sistem fluida dinamik begini ya, gelap deh) selalu tidaksempurna dan selalu memerlukan penyesuaian dengan kondisi lapangan.

Begitu dulu yang bisa saya sampaikan. Semoga bermanfaat.

roeddy setiawan

Pak Nugroho,

Saya sependapat dengan anda. shock wave makin lama akan makin kecil di keduaujung nya. kalau source kebocorannya kecil seperti yang biasanya didapat daripitting agaknya sulit terdengar apa lagi kalau hanya "one shoot"

issue yang kedua yah memang benar, sudah declare emergency pipeline leak, tahunya false alarm wah bisa hilang bonus nya (kidding).

Pendapat pak Nugroho benar, saya kira yang terbaik harus komposit method, satusama lain saling melengkapi. antara accurate material ballance dengan methodeyang lain.

Documents

Pipeline Gas Detection