How to perform pressure test of FRAMO submersible Cargo Pump

If the purging routine has detected a cargo leakage (more than 2 litre / day), and the evaluation indicates that action must be taken, first thing you have to do is to identify the leakage. The best way is to pressure test the pump’s cofferdam.




Cargo Leakage

If a cargo leakage is detected the complete cargo pump’s cofferdam has to be pressure tested to identify the leak. The crew on some ships start to automatically change the pump’s cargo seal as soon as there is a cargo leakage - although the leak may be somewhere else. This is waste of time and money. So always identify where you have a leak first!

The cofferdam can be pressure tested by blinding off the purging medium relief valve by means of a rubber gasket. Dismantle the cofferdam’s riser pipe flange on the top cover plate and install a test flange with pressure gauge (see figure 1). Connect the purging medium to the test flange and increase the pressure to 3 bars. After approximately 5 minutes check all flanges around the cargo seal, riser pipe and all other connections for possible leakages. Use soapy water for better detecting of the possible leakage.

Note: If the cargo leakage is not possible to identify and the 3 bar pressure is stabilized for a long period of time during the pressure testing, it is still possible that the cargo seal in the pump is worn out and have to be changed. The reason could be that the 3 bars pressure in the cofferdam is pressing the upper lip (facing the cofferdam) around the pump shaft. Dismantle the cargo seal for control. If this is not the case and the cargo leakage is not possible to detect, you have to split the cargo pump and pressure test the main components separately.

Hydraulic Oil Leak

If the cargo pump has a hydraulic oil leak you normally have to split the pump to identify the leak. A hydraulic oil leak is very rare under normal conditions, but if a hydraulic oil leak does occur, there could be three reasons: a) Hydraulic oil seal - the life time is normally very high (>10.000 running hours). b) Crack in pipe stack - can occur if the cargo pump is vibrating heavily for some abnormal reasons. c) Corrosion attack in the seal ring grooves can occur after long service.


Good practices

Acid cargoes : After discharging and purging is finished, it may be an advantage to circulate fresh water through the cofferdam to remove all residues after a leakage.

Phenol, caustic soda etc. : A circulation of hot water through the cofferdam can avoid clogging.

Polymerising cargoes (TDI, MDI) : Fill cofferdam with dioctyl phthalate(DOP) to limit the risk of blocking the cofferdam.

Crystallizing cargoes (molasses, etc.) : Fill cofferdam with fresh water. The cofferdam may also be arranged with a small water circulation





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Other info pages

Draegar Chemical detector tubes use and reading correction guideline
These instruments, often referred to as Draeger tubes, normally function by drawing a sample of the atmosphere to be tested through a proprietary chemical reagent in a glass tube. The detecting reagent becomes progressively discoloured if a contaminant vapour is present in the sample. The length of the discoloration stain gives a measure of the concentration of the chemical vapour which can be read from the graduated scale printed on the tube. Detector tubes give an accurate indication of chemical vapour concentration, whatever the oxygen content of the mixture

Requirements of various grade chemical cargo heating
: The voyage orders will contain heating information, if heating is required. As a rule the final heating instructions are given by the Shipper in writing to the Master / Chief Officer in the port of loading. If those written instructions are not given, the master should request them and issue a Letter of Protest if they are not received at departure. In the latter case the management office should be immediately informed.


Recommended temperature monitoring equipments onboard
:Temperature sensors are fitted so that the temperature of the cargo can be monitored, especially where required by the IBC Code. It is important to know the cargo temperature in order to be able to calculate the weight of cargo on board, and because tanks or their coatings often have a maximum temperature limit. Many cargoes are temperature sensitive, and can be damaged by overheating or if permitted to solidify. Sensors may also be fitted to monitor the temperatures of the structure around the cargo system.

Cargo instruments
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Liquid level gauges
:The accuracy required of chemical carrier level gauges is high because of the nature and value of the cargo. To limit personnel exposure to chemicals or their vapours while cargo is being handled, or during carriage at sea, the IBC Code specifies three methods of gauging the level of a liquid in a tank - open, restricted or closed

Overflow control
:Certain cargoes require the designated tank to be fitted with a separate high level alarm to give warning before the tank becomes full. The alarm may be activated by either a float operating a switch device, a capacitive pressure transmitter, or an ultrasonic or radioactive source. The activation point is usually pre-set at 95% of tank capacity.

Oxygen analysers
:Oxygen analysers are normally used to determine the oxygen level in the atmosphere of an enclosed space: for instance, to check that a cargo tank can be considered fully inerted, or whether a compartment is safe for entry.

Vapour detection
:Ships carrying toxic or flammable products (or both) should be equipped with at least two instruments that are designed and calibrated for testing the gases of the products carried. If the instruments are not capable of testing for both toxic concentrations and flammable concentrations, then separate sets of instruments should be provided.

Alarm circuit
:An important feature of many modern measurement and control instruments is the ability to signal a particular situation. This can be a main operational alarm that gives an indication of a pre-set situation such as liquid level in a tank, or a malfunction alarm indicating a failure within a sensor's own operating mechanism. The designs and purposes of alarm and shutdown circuits vary widely, and their operating system may be pneumatic, hydraulic, electrical or electronic. Safe operation of plant and systems depends on the correct operation of these circuits and a knowledgeable reaction to them.

Gas freeing
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Reference publications

• Equipment Manufacturers Instruction Manuals
• MARPOL – 73/78 (latest consolidated edition)
• International Safety Guide for Oil Tankers and Terminals (ISGOTT)
• CFR 33 parts 125 to 199
• Ship to Ship Transfer Guide (Petroleum)
• MSDS for particular cargo carried
• Chemical Tank Cleaning Guide

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