Why is so important to pressure test the vessel’s bunker lines?

Vessel’s bunker line pressure test is a procedure of the outmost importance which cannot be emphasizes enough, although is ignored and avoided by many engineers sometimes due lack of time, lack of knowledge or fear that something would go wrong during test. Is very important to remember that the whole purpose of this periodical test is exactly to find if something is wrong with the fuel oil bunkering system and to take all necessary actions to remediate the faults and defects within.

Chief Engineer is responsible for performing the pressure test of the bunker line on an annual basis when each transfer pipe onboard a vessel must be tested under static liquid pressure, at least 1.5 times the maximum allowable working pressure (MAWP). Special attention should be paid to flange joints, valve gland packing, pump seals etc.

Hydrostatic test is a test conducted by filling a space with a liquid to a specified head. Unless another liquid is approved, the hydrostatic test consists of filling a space with either fresh or sea-water, whichever is appropriate for the space being tested. This kind of test is usually performed during vessel’s periodical special survey (dry docking) using fresh water, but sometimes needs to be done also onboard.

Bunker line hydrostatic test performed in dry dock

MAWP is considered to be the design relief valve pressure setting of the relief valve on the bunker transfer pump. In the absence of the relief valve the MAWP should be taken to be 5.0 kg/cm2.

Bunker line tested @5 kg/cm2

In order to perform the test onboard the following should be taken into consideration:

  • A “Permit to Work” should be issued and a “Risk Assessment” must be carried out.
  • Before conducting the test, all scuppers should be sealed and adequate oil spill equipment should kept ready on deck.
  • The test should be performed for a period of 10 minutes under a constant hydrostatic load.
  • The pressure rating for pipe line material should not be exceeded. This pressure can be found and verified into the vessel’s bunker plan and/or piping diagram.
  • During testing onboard bunker transfer pump may be employed for the test. If the transfer pump is a positive-displacement type, it may be stopped when the required test pressure is reached as it should not permit backflow, therefore valves before and after pump should be closed after desired pressure has been reached. If a centrifugal pump is used for testing, constant running is required to ensure the necessary pressure is maintained.
  • The test should be conducted while underway at sea at least 200 nm from shore during day light.
  • Similar test procedure applies for fuel oil and lube oil bunker lines.
  • After the test, the date and test pressure should be stenciled on the pipe lines and deck at prominent locations.
  • The stencil should be: ”Hydro Test Date: xx/xx/xxxx Pressure: xx kg/cm2.

The actual testing procedure should comprises of the following steps:

  • Minimum pressure test must be 4 kg/cm2.
  • The bunker line relief valve if fitted must be removed and a blank with a drain valve must be fitted. As an alternative, the relief valve set pressure can be increased and test the bunker line pressure to a value at least 1.5 times, the normal operating set pressure of the relief valve. In the absence of the relief valve the MAWP should be taken to be 5.0 kg/cm2.
  • At the bunker station, fit a flange, fitted with pressure gauge and a connection for a suitable hand pump. The connection should be fitted with a gauge/cock for pressure monitoring. You must ensure that the gauge is verified and calibrated.
  • A communication between engine room and deck must be established and personnel must be arranged to monitor for any leaks on deck and engine room.
  • Use the transfer pump to fill bunker lines up to the manifold. Purge the lines via valves/cocks on manifold.
  • After the line is filled with oil, the pump valves and system valves must be closed. A hydraulic hand pump can be connected to the manifold to build up the pressure or same can be done with the transfer pump but caution must be taken in order not to damage the pump.
  • Maintain the pressure for 10 minutes and check the entire system for leaks.
Failure bunker line on deck during annual pressure test
  • After completion of test drain the pressure into the overflow tank through the relief valve connection or by slowly opening the valve to an empty bunker tank.

It is very important to remember that it is not allowed to test the system by air and by doing so it will makes the test worthless and void. If vessel intend to bunker in United States, it must provide the written records of the date and result of the most recent hydrostatic test and inspection of the bunker lines/transfer system as required by 33 Code of Federal Regulations (CFR) 156.170.

The Coast Guard recognizes that achieving the test pressure of 1.5 times MAWP for annual bunkering test on vessels is often impractical while vessel are in service or outside shipyards where special equipment may not be available. Therefore, the Coast Guard will continue to accept alternatives as described below:

  • Compliance with the requirement is economically or physically impractical
  • The vessel operator submits a written request for the alternative at least 30 days before operations under the alternative proposed, unless the Captain of the Port authorizes a shorter time.
  • The alternative provides an equivalent level of safety and protection from pollution by oil or hazardous material, which is documented in the request.

The US Coast Guard allows for acceptance of alternative test pressure of not less than 100% MAWP for annual bunker test, provided that a 150% MAWP test of the piping is conducted at least twice in any five years period. It is envisioned that the 150% MAWP test will be conducted during vessel’s drydock periods at the discretion of the owners or operators.

In conclusion, periodical test of bunker lines are very important and it must be done diligently and be a part of vessel’s periodical safety checks. Although is a Chief Engineer responsibility, every engineer must be familiar with the legal and testing procedure requirements as they are involved into the daily vessel’s operation and bunkering process. As I said, it can be emphasized enough the importance of performing the test, as failure to do so can lead to serious consequences for the vessel and crew.

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