LPG carrier cargo pipeline & tank inspection/ test procedure
Tank inspections requirement
Cargo tanks are to be inspected internally during every dry-docking and in circumstances where a particular tank is required to be gas freed for repairs. All other tanks, including ballast and void spaces must be internally inspected on a 12-month cycle to establish the condition of steelwork, pipework, fittings and coatings of anodes, as applicable.
In order to assist in this process and ensure a uniform and objective framework of reporting, the publication “condition Evaluation & Maintenance of Tanker Structures” is to be referred to before commencing an inspection. In addition, pocket-sized copies of the LR publication “Tank Coatings Condition Guide” will also be provided onboard.
Defects must be reported as early as possible to allow repairs to be budgeted and scheduled. Wherever possible, the report is to be supported with photographic evidence. However, only cameras that are intrinsically safe are to be used. Where there is doubt as to the suitability of the camera, the management office is to be advised.
Particular attention is to be paid to examine and remove any debris which may be left inside the cargo tanks after a repair period. Such debris may cause damage to filters, pumps and valves on both ship and shore installations. Any water accumulated should also be removed in order to avoid the formation of hydrates.
It is appreciated that due to certain ship designs and/or trading patterns that the six-month cycle may not be practical. In such cases, a suitable inspection cycle must be agreed to, in association with the fleet cell and followed. Such an agreement must be documented.
Cargo pipeline inspection / test procedure
Cargo pipelines are to be inspected and tested on a regular basis with any defects immediately reported to the management office. The condition of pipelines on semi-refrigerated LPG carriers is often difficult to ascertain due to the presence of insulation material, however, the following procedures should be followed:-
Checks During Loading / Discharging
At least once in every 12 months period, ship staff should undertake a thorough visual examination of the cargo and process pipelines, valves (including pressure relief valves and drainage arrangements), piping anchor supports, fittings, liquid/vapour hoses and expansion bellows. Furthermore, a pressure test should be carried out after a cargo change over, particularly if the cargo system has been broken to alter tank segregation.
A pressure test to a minimum of the designed maximum working pressure for the pipeline is to be carried out. The preferred medium for this test is cargo, as opposed to nitrogen, due to the quantity of pressurising medium required on larger vessels. The system should be checked for leaks and if there are any deficiencies noted, the management office is to be advised immediately. If a leak is suspected, the insulation must be removed in the immediate area of the suspected leak.
Prior to carrying out this test, the settings for the line pressure safety valves are to be ascertained. During the test, it is important that the maximum pressure does not exceed 85% of the safety valve activation pressure.
The inspection and testing routine should be entered into the PMS onboard and records maintained up-to-date.
Test Procedure in Dry-dock
During period of dry-docking, all cargo and process piping systems, including valves, actuators and compensators, should be opened for examination as deemed necessary by the Class surveyor, to ascertain the condition of the pipes. A recognised shore-based company is to be employed to carry out this close-up inspection as insulation may need to be removed and subsequently replaced.
Normally, if any doubt exists regarding the integrity of the piping, based upon visual examination, , where deemed necessary by the Class Surveyor, a pressure test to 1.25 times MARVS (Maximum Allowable Relief Valve Setting) for the pipeline is carried out on the suspected section of pipe. After reassembly and any repairs, the complete piping system is to be tested to a minimum of the designated working pressure and checks made for leaks.
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