Untuk menguji kekuatan (strength), keutuhan (integrity) dan ketidakbocoran sambungan-sambungan dari suatu sistem perpipaan yang sudah kita rancang bangun (designed and installed) perlulah dilakukan pressure test/pressure leak test sebelum sistem perpipaan masuk ke dalam system.

Atau mengutip kalimat dari buku “Piping Handbook”, sixth edition (Mohinder L. Nayyar), chapter B4 – Stress Analysis of Piping Systems by C. Basavaraju & William Saifung Sun, yang mengatakan bahwa to assure the integrity and leak tightness of a piping system is required pressure test be performed prior to placing the piping system in service. Sedangkan mengutip dari ASME B31.8 – Gas Transmission and Distribution Piping Systems, 2010 edtion, bahwa pressure test is to validate integrity of piping system (pipes and equipments) and detect construction defects and defective materials.

Pressure leak test dilakukan tentunya setelah sistem perpipaan sudah melewati yang namanya visual check dan NDT (non destructive test – tes tanpa merusak). Pressure leak test sendiri adalah test dengan merusak atau DT (destructive test). Sedangkan NDT hanyalah memeriksa kualitas beberapa/semua sambungan pipa, misalnya dengan memakai metoda liquid penetrant test, magnetic particle test, ultrasonic test, radiography test, dll.

Untuk sistem perpipaan ada banyak standar internasional yang dipakai untuk melakukan pressure leak test, namun untuk pembahasan kali ini akan sedikit dibahas persyaratan-persyaratan pressure leak test dari standar-standar internasional yang sering digunakan di suatu plant.

 

ASME B31.3 – PROCESS PIPING

Persyaratan-persyaratan yang diberikan oleh ASME B31.3 – Process Piping, 2010 edition (para. 345):

  • Where the owner considers a hydrostatic leak test impracticable, either a pneumatic leak test or a combined hydrostatic-pneumatic test may be substituted, recognizing the hazard of energy stored in compressed gas.
  • Where the owner considers both hydrostatic and pneumatic leak testing impracticable, the alternative specified in para. 345.9 may be used if both of the following conditions apply:

(1) A hydrostatic test would damage linings or internal insulation, or contaminate a process which would be hazardous, corrosive, or inoperative in the presence of moisture, or would present the danger of brittle fracture due to low metal temperature during the test

(2) Or would present the danger of brittle fracture due to low metal temperature during the test

  • Where the unless specified in the engineering design, lines open to the atmosphere, such as vents or drains downstream of the last shutoff valve, need not be leak tested.
  • (Para9.1) Welds, including those used in the manufacture of welded pipe and fittings, which have not been subjected to hydrostatic or pneumatic leak tests in accordance with this code, shall be examined as follows:

(1) Circumferential, longitudinal, and spiral groove welds shall be 100% radiograph examined or 100% ultrasonically examined

(2) All welds, including structural attachment welds, not covered in (a) above, shall be examined using the liquid penetrant method or, for magnetic materials, the magnetic particle method.

  • (Test fluid)

(1) The fluid shall be water unless there is the possibility of damage due to freezing or to adverse effects of water on the piping or the process. In that case another suitable nontoxic liquid may be used. If the liquid is flammable, its

flash point shall be at least 49°C (120°F), and consideration shall be given to the test environment.

(2) The gas used as test fluid, if not air, shall be nonflammable and nontoxic.

  • (Test pressure)
    • Hydrostatic leak test shall be not less than 1.5 x MAWP (design pressure)
    • Pneumatic leak test shall be not less than 1.1 x MAWP (design pressure)
  • A leak test shall be maintained for at least 10 min, and all joints and connections shall be examined for leaks.
  • (Temporary pipe supports)

Piping designed for vapor or gas shall be provided with additional temporary supports, if necessary, to support the weight of test liquid.

  • (Piping with vessel as a system)

(1) Where the test pressure of piping attached to a vessel is the same as or less than the test pressure for the vessel, the piping may be tested with the vessel at the piping test pressure.

(2) Where the test pressure of the piping exceeds the vessel test pressure, and it is not considered practicable to isolate the piping from the vessel, the piping and the vessel may be tested together at the vessel test pressure, provided the owner approves and the vessel test pressure is not less than 77% of the piping test pressure calculated in accordance with para. 345.4.2(b).

 

ASME B31.1 – POWER PIPING

Persyaratan-persyaratan yang diberikan oleh ASME B31.1 – Power Piping, 2002 edition (para. 345) hampir sama dengan yang diberikan oleh ASME B31.3 – Process Piping, 2010 edition, bedanya hanyalah di test pressure untuk pneumatuic test (para. 137.5.5), yaitu bunyi sbb:

  • (Required Pneumatic Test Pressure).

The pneumatic test pressure shall be not less than 1.2 nor more than 1.5 times the design pressure of the piping system. The test pressure shall not exceed the maximum allowable test pressure of any non-isolated component, such as vessels, pumps, or valves, in the system.

 

ASME B31.4 – LIQUIDS PIPELINE TRANSPORTATION

Persyaratan-persyaratan yang diberikan oleh ASME B31.4 – Liquids Pipeline Transportation, 2009 edition (para. 437.4):

– Portions of piping systems to be operated at a hoop stress of more than 20% of the specified minimum yield strength of the pipe shall be subjected at any point to a hydrostatic proof test equivalent to not less than 1.25 times the internal design pressure at that point for not less than 4 hr. When lines are tested at pressures that develop a hoop stress, based on nominal wall thickness, in excess of 90% of the specified minimum yield strength of the pipe, special care shall be used to prevent overstrain of the pipe.

– API RP 1110 may be used for guidance for the hydrostatic test.

– The hydrostatic test shall be conducted with water, except liquid petroleum that does not vaporize rapidly may be used

– If the testing medium in the system will be subject to thermal expansion during the test, provisions shall be made for relief of excess pressure. Effects of temperature changes shall be taken into account when interpretations are made of recorded test pressures.

– After completion of the hydrostatic test, it is important in cold weather that the lines, valves, and fittings be drained completely of any water to avoid damage due to freezing.

– Carbon dioxide pipelines, valves, and fittings shall be dewatered and dried prior to placing in service to prevent the possibility of forming a corrosive compound from carbon dioxide and water.

 

ASME B31.8 – GAS TRANSMISSION AND DISTRIBUTION PIPING SYSTEMS

Persyaratan-persyaratan yang diberikan oleh ASME B31.8 – Gas Transmission and Distribution Piping Systems, 2010 edition adalah sesuai dengan table 841.3.2-1:

 

ASME B31.8

Agar agan-agan tidak bingung apa itu kelas lokasi (location class) pada standar ASME B31.8, tabel dibawah ini akan menjelaskan batasan-batasan untuk setiap kelas lokasi:

ASME class

Dari kelas lokasi (location class) ini tentunya akan membedakan kriteria desain setiap lokasi yang dilewati oleh suatu pipeline dan juga besaran masing-masing pressure test-nya.

 

Pertimbangan selanjutnya dalam pemilihan pressure leak test, apakah akan menggunakan hydrostatic leak test atau pneumatic leak test adalah sbb:

  1. Service fluids

Pada umumnya, apabila servis fluidanya adalah fluida bertekanan (compressible fluid) seperti instrument air, hydraulic system, nitrogen system, natural gas piping disarankan menggunakan pneumatic leak test untuk mencegah servis fluida terkontaminasi dengan air setelah put in system, hal yang sama dianjurkan juga untuk fuel oil.

  1. Test pressure

Dengan alasan safety, beberapa plant menganjurkan untuk tekanan tinggi tertentu tidak menggunakan pneumatic leak test tapi hydrostatic leak test untuk mencegah dampak yang diakibatkan oleh compressible fluid bila terjadi kebocoran pipa. Untuk menghindari adanya kontaminasi air maka selajutnya akan dilakukan pengeringan (drying) dengan compressed air.

  1. Pipe materials

Umumnya plastic pipes seperti HDPE, PVC, FRP, dll tidak dianjurkan menggunakan pneumatic leak test karena sifat fluidanya yang mampu tekan (compressible fluids).

 

The followings are hydrostatic leak test sequences (but not limited to):

  • Install flanges and blind flanges at the end of pipeline to be hydrostatic test
  • Install fill-up water line (supposed closed to existing water pump) and also install small bore connection line for LPD (low point drain), HPV (high point vent) and instruments hook-up
  • Killed punch list along the pipeline prior to hydrostatic test
  • Fill up water along the pipeline by water pump, venting valve opened to ensure no air trap along the pipeline
  • Warning sign along the hydro-tested pipeline (as restricted area during activities), to prevent any personals closed to the hydro-tested pipeline area.
  • Ensure hydrostatic equipments and tools (dead weight tester – DWT, pressure gauge, temperature gauge, pressure recorder, temperature recorder, pressure pump) already calibrated and inspected.
  • Perform hydrostatic leak test, and if any pressure drop do checking to know more positions of any leakages along the pipeline and do repair.
  • Record pressure, temperature, etc… And if hydrostatic leak test OK do reporting!

 

Hal-hal yang harus di record (minimum requirements) ketika melakukan pressure leak test adalah sebagai berikut (ASME B31.3 – Process Piping, 2010 edition, para.345.2.7):

(a) Date of test

(b) Identification of piping system tested

(c) Test fluid

(d) Test pressure

(e) Certification of results by examiner

 

Terakhir yang tak kalah pentingnya, karena sesuai dengan regulasi pemerintah melalui Department of Mines and Energy of the Republic Indonesia, Director General of Oil and Gas, The Director General of Oil and gas Decree Nor: 84.K/38/DJM/1998, bahwa pipa penyalur/distribusi (pipeline) haruslah diinspeksi langsung dan kemudian disertifikasi untuk memperoleh Sertifikat Kelayakan Penggunaan Peralatan (SKPP) dari perwakilan pemerintah yang terkait, maka sebelum dilakukan hydrostatic leak test, wajiblah untuk mengundang perwakilan pemerintah yang terkait untuk hadir di dalam pelaksaaannya serta tentunya melengkapi semua dokumen-dokumen yang diperlukan untuk sertifikasi tersebut (sesuai dengan yang disebutkan di dalam The Director General of Oil and gas Decree Nor: 84.K/38/DJM/1998) yaitu seperti berikut (tapi tidak terbatas pada):

  • Pipeline design detail (fluid service, specific gravity, MAOP, MAWP, operating temperature, design temperature, etc)
  • Calculation (pipe diameter, pipe wall thickness, pipe supports calculation, testing pressure calculation, etc)
  • Specification of material used (mill certificates)
  • WPS/PQR, welder certificate, etc
  • NDT records
  • SOP of pressure leak test
  • Completeness of testing equipments and tools (calibration is mandatory)
  • Pressure test record (for geothermal steam distribution pipeline, minimum holding times of pressure leak test is 2 hours)

 

Punten kang! karena sesuai dengan judulnya maka berikut akan ditampilkan proses eksekusi pekerjaan hydrostatic leak test sesuai dengan ASME B31.3 – Process Piping, dimana kebetulan plant memakai standar tersebut untuk melakukan pekerjaan ini.

01

Picture 01: 36” pipeline to be hydrostatic leak tested

 

02

Picture 02: Install flanges and blind flanges to break out hydrostatic line from exiting line, to prevent any damage of new valves and disruption to online pipeline

 

03

Picture 03: Additional temporary pipe support (see right side) for hydrostatic leak test

 

04

Picture 04: Warning sign during hydrostatic leak test

 

05

Picture 05: Fill-up water pump

 

06

Picture 06: Pressure water pump

 

07

Picture 07: Pressure recorder (ITT Barton chart) and dead weight tester (DWT)

 

08

Picture 08: Hydrostatic leak test activities

 

09

Picture 09: Hydrostatic leak test activities is being witnessed by government representative and inspection’s third party

 

10. Hydrostatic leak test diagram

Picture 10: Hydrostatic leak test diagram

 

 

Catatan penting saat eksekusi:

  • Range tekanan pada Pressure Gauge (PG) yang akan digunakan adalah 1.5 ÷ 4 MAWP (design pressure)
  • DWT (dead weight tester) kudu wajib, karena lebih valid dalam me-record pengukuran tekanan dibandingkan record tekanan dari Barton chart maupun PG-1 (high point) dan PG-2 (low point), ini dikarenakan perubahan cuaca yang tidak stabil (fluctuation) selama test berlangsung.
  • Ketika ada valves yang harus terkoneksi saat berlangsungnya test, misalnya valves pada CDP (condensate drain pot), valves tersebut jangan di fully closed karena akan merusak stem of valve akibat tekanan hydrotest, tapi cukup dikasih plug atau blind flanges pada ujungnya.

 

 

Dan berikut lampiran “Hydrotest Calculation” sebagai data pendukung untuk eksekusi pekerjaan ini, semoga membantu:

Hydrostatic Leak Test Calculation