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Chapter 4

Inspection and Maintenance Work during Voyage

§ Inspection and maintenance work during voyage

Maintenance work should be carried out periodically during voyage in order to ensure safety.

1. Inspection and maintenance of vent riser (P.4-3 to P4-4) To enable the vent riser to safely release vapors from the cargo oil to the atmosphere, it is provided with safety equipment such as a flame screen that prevents entry of flame and equipment to extinguish fire that may occur due to a bolt of lightning. The vent riser should be inspected and maintained periodically to ensure that it is in a satisfactory condition.

2. Inspection and maintenance of breather valve (P.4-5 to P.4-11) The breather valve is a safety valve of the tank. It is used in the vent riser and in independent vents. The breather valve may become stuck when impurities included in the vapors adhere to it. In such cases, it may not be able to maintain its designed performance. It should be inspected and maintained periodically so that it works satisfactorily at all times.

3. Inspection and maintenance of P/V breaker (P.4-12 to P.4-14) The P/V breaker is a safety device installed to prevent damage to the tank. The level of fresh water or the level of mixture of fresh water and antifreeze solution sealed in the breaker should be adjusted at all times to the proper value so that the P/V breaker activates correctly at the set pressure. The sight glass should also be maintained properly so that accurate readings can be taken.

4. Inspection and maintenance of hydraulically operated valves and hydraulic system

(P.4-15 to P.4-25) The valve is an important equipment in a tanker so much so that it may be considered the "life" of the tanker. If a valve does not work, neither loading nor discharging can be performed. Accordingly, the functional test of valves should be carried out and the operation of valves should be confirmed before entry into port.

5. Measurement procedure, inspection and maintenance of gas detectors (P.4-26 to P.4-29) The most important function of the gas detector is to prevent explosion and combustion and thereby ensure safety of life. The detector to be used and its measurement range should be appropriately selected according to the gas to be measured and the environment at the location of the gas. The detector is an important equipment related to the safety of life and the safety of the ship. Its handling operation should be thoroughly studied and it should be inspected and maintained so that it can be used at any time.


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6. Functional test of bilge alarm (P.4-30) The functional test of bilge alarm in the pump room should be carried out at an appropriate period before entering the loading port/discharging port. The results of the test should be recorded.

7. Functional test of high high level alarm (P.4-31 to P.4-32) The functional test of high high level alarm for preventing overflow of cargo tank should be carried out at an appropriate period before entering the loading port, and the results of the test should be recorded.

8. Leak test of sea chest valve (P.4-33 to P4-34) The leak test of sea chest valve should be carried out for preventing oil spills. The results of the test should be recorded.


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1. Inspection and maintenance of vent riser

Click here to view video – 085.mp4

1.1 General The vent riser is provided with the accessory equipment mentioned below so that dangerous vapors generated from cargo oil can be released safely to the atmosphere based on the prescribed arrangement/height.

1) Drain valve 2) Maintenance hole 3) Flame screen (made of wire gauze) 4) Breather valve

1.2 Inspection and maintenance of breather valve and maintenance hole

A drain valve and maintenance hole are provided at the lower part of the vent riser. Open the drain valve and drain out the contents every voyage. Sometimes, oil is mixed in the drain, therefore, the drain should be collected in buckets. Sometimes, rust may also accumulate at the bottom of the vent riser. Once every two to three voyages, the maintenance hole should be opened up, inspected and cleaned its inside.

1.3 Inspection and maintenance of fire extinguishing equipment The vent riser has a portable carbon dioxide fire extinguisher for fighting fires. A connection for carbon dioxide fire extinguishing hose is provided at the lower part of the vent riser. This connection should be inspected and maintained.

1.4 Inspection and maintenance of flame screen (made of wire gauze) A flame screen is fitted on the upper part of the vent riser for preventing entry of flame from the outside and as a measure against a bolt of lightning. If the flame screen becomes clogged with rust or soot, the tank pressure may not be released properly during loading operation and hinder the cargo handling operation. Thus, the condition of the flame screen should be checked and its maintenance should be carried out during each voyage. If rust or soot is found to have accumulated on the flame screen, it can also be concluded that soot or rust has been generated in the IGS, the IGS line or inside the tank.

1.4.1 Maintenance period The flame screen of the vent riser should be removed during each voyage, cleaned, inspected and if necessary, repaired. Generally, to ensure safety during the work, this work is performed during the outward voyage when the tank pressure is steady.

1.4.2 Replacement work The mesh size of the wire gauze is very fine (a 30-mesh (overlapped if 20-mesh) should be fitted according to Class NK Rules) and it is liable to be clogged and damaged easily. After cleaning the screen, it should be inspected, and if necessary, the flame screen should be renewed. Generally, spare flame screens are available on board which can be used to replace defective screens, thereby ensuring prompt response and safety of work. The precautions mentioned below should be taken during the replacement work.

1) Release of gas to the atmosphere during the replacement work is prohibited. 2) The tank pressure and the trend of change in this pressure should be studied and safety verified by

checking for the presence of gas leaks. 3) Spare parts and hoisting rope should be kept ready. 4) The prescribed procedure for high altitude work should be strictly observed to. 5) One group consisting of at least two persons should perform the work.

http://www.nyk-training.com/vlccstarship/videoplayer.jsp?file=085.wmv


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6) Before cleaning the flame screen, the presence of foreign matter such as soot or rust should be checked.

1.4.3 Installed location The main installed locations of the flame screens in hazardous areas on the deck are as listed below.

1) Vent riser 2) Independent vent (Flame screens are not installed in high velocity exhaust vents since these vents satisfy the rule requirement for preventing entry of flames.) 3) Air vents in ballast tanks and fuel tanks 4) Exhaust fan in pump room 5) Ullage hole 6) P/V breaker

* Difference between flame arrestor and flame screen

The differences between a flame arrestor and a flame screen, as well as the equipment used on board the ship should be thoroughly understood. A flame screen is generally provided in vents of most crude oil tankers. The differences between a flame arrestor and a flame screen are as given below.

1) Flame arrestor A flame arrestor is a permeable matrix made of heat resistant material such as metal or ceramics that never heated up until ignition temperature of the combustible gas on the other side of the arrestor. 2) Flame screen A flame screen is a removable or fixed device made of one or more corrosion-resistant wire gauze screens with very fine mesh that prevents sparks entering from tank openings or vent openings, or protects the passage of flames in short-time through these openings.


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2. Inspection and maintenance of breather valve 2.1 General

The breather valve is a safety valve installed to protect damage to cargo tank from excessive positive or negative pressure in the tank that arises due to external conditions such as air temperature or seawater temperature during a voyage. Thus, the breather valve is constructed such that it cannot cope with the discharged gas capacity during loading. Also, the breather valve has a manually operated lever that can be set only at two positions: "Open" and "Auto." Its construction is regulated by classification society rules and it cannot be closed positively. In some tankers, independent vents are not provided with breather valves but are provided with high velocity exhaust vents (that discharge vapors at a velocity of 30 m/sec or more and disperse them to the atmosphere). If these vents have a capacity less than the permissible venting capacity (1.25 times the loading rate), then they can be used during the cargo handling operation. This system is called the independent venting system and is used generally in products/chemical tankers where contamination by vapors is not permitted.

2.2 Installed location

Breather valves are installed at the locations mentioned below. 1) In vent pipes attached to each tank (independent vents) 2) Vent riser 3) Vent branch pipe (bypass line of IG branch valve)

2.3 Inspection and maintenance of breather valve for independent vent

2.3.1 Construction (weight type) Two gravity valves namely pressure valve and vacuum valve are installed. When the positive pressure in the tank becomes excessive, the pressure valve activates and releases vapors to the atmosphere. Conversely, when the negative pressure in the tank becomes excessive, the vacuum valve activates, allows outside air to enter the tank and maintains constant pressure in the tank. A flame screen is installed in the intake port of the vacuum valve to prevent entry of flames. (See Fig. N-4-1.)


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Fig. N-4-1 Breather valve for independent vent


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2.3.2 Pressure setting The standard pressure settings are 16 kPa/-5kPa (about 1,600 mmA1/-500 mmAq). (The ship's pressure settings should be adhered to.)

2.3.3 Inspection and functional test

1) The sticking of the pressure valve and the vacuum valve can be confirmed by appropriately operating the round handle at the upper part or the lever handle at the lower part of the breather valve unit. This test helps prevent defective operation of the breather valve due to sticking. (There are various types including the type in which the valve can be directly lifted by the tip of the finger, a screw type and a push-down type)

2) In principle, the test at the pressure setting should not be carried out with the breather valve in the fitted condition. After the opening up and maintenance of the valve, the functional and leak tests should be carried out at the positive pressure setting using the test kit (see Fig. N-4-2) prepared by the ship. The negative pressure tests can be carried out only when the ship is dry-docked because eductor equipment is necessary for creating a vacuum.

3) If a small leak occurs it can be stopped by operating the round handle or the lever handle several times.


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Fig. N-4-2 Test Kit for Independent Breather valve

2.3.4 Opening up and maintenance of the breather valve


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One round of opening up and maintenance operations of the breather valve every six months is recommended. (at least within a year). A double hull ship generally has 17 tanks, which means maintenance of 4 to 5 tanks should be planned per voyage. Spare parts should be efficiently utilized and should be sequentially replaced during the maintenance (about 30 minutes are required for replacement). The removed breather valve should be opened up, the soot and rust removed and the valve seat should be inspected for scratches and other damage by penetration checks. If scratches are detected, then the contact surfaces should be faced. The condition of the flame screen should also be inspected simultaneously. If the screen is clogged or corroded, it should be replaced. Gaskets should be renewed whenever possible. The internal parts of the breather valve are extremely susceptible to corrosion. The inner surface of the valve should be coated with tar epoxy paint and measures to prevent corrosion should be adopted. Details of the spare parts and the replacement procedure are given below.

1) Check the tank pressure. Adjust the tank pressure beforehand so that the gas required for adjusting

the tank pressure is not released during the work. 2) Fully open the IG branch valves of tanks other than tanks in which the independent vents are to be

replaced. 3) Open the vent riser valve gradually until it is fully open and release the tank pressure.

4) When the tank pressure has been relieved, remove the breather valve. 5) Fit the spare part and fully close the vent riser valve. 6) Gradually open the IG branch valve of each tank, then pressurize the tank which is replaced the

breather valve. 7) Confirm that there is no leak in the independent vent that has just been replaced. Leaks can be

identified easily by using soap solution during the leak test.

2.3.5 Maintenance period Generally, when the ship sails out from discharging port in the Far East/Persian Gulf or Red Sea trade, the tank pressure tends to rise. Maintenance can be carried out at this stage. During the homeward voyage, replacement is scheduled on the day for topping up.

2.4 Inspection and maintenance of breather valve for common vent riser

2.4.1 Construction (piston type) With a combination of one valve and a piston, the breather valve has two functions: release to the atmosphere and air intake. When the pressure in the tank is excessive, the piston rises, opens the valve and releases the vapors to the atmosphere. When the pressure in the tank becomes negative, only the valve opens because of the difference in pressure. The outside air is drawn in and the tank pressure is maintained constant. The main feature of the piston type arrangement is that it is compact since there is only one valve and the release capacity is large. (See Fig. N-4-3.)

The vent riser valve should be kept fully open until the replacement work is completed.


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Fig. N-4-3 Breather valve for common breather valve


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2.4.2 Pressure setting The standard pressure settings are 14 kPa/-5kPa (about 1,600 mmA1/-500 mmAq). (The ship's pressure settings should be adhered to.)

2.4.3 Functional test

1) Checks should be carried out each voyage to detect whether the valve is stuck. This can be verified by appropriately operating the lever handle on the outside of the valve body.

2) The test of the positive pressure setting at which the valve activates should be carried out when the tank pressure rises during the loading voyage. However, the main role of the breather valve is its function as a safety valve. Other than the test of pressure setting at which the valve activates, the breather valve should not be activated by opening up the vent riser valve manually. This is to prevent the occurrence of abnormalities such as damage to the breather valve or malfunction caused by influence of foreign matters . The functional test during the ballast voyage is not generally carried out because it takes long time to stop breathing upon activate the valve so that the vapor capacity of cargo tank is huge amount.

In practice, the functional test should not be performed by lowering the pressure in the tank to a negative value. 3) If the tank pressure rises during the homeward voyage, which is the loading voyage, and is allowed

to remain as is, the valve activates and releases pressure (starts acting) at about 14 kPa (about 1,400 mmAq) and stops when the pressure reaches 7 to 9 kPa (about 700 mmAq to 900 mmAq).

4) If a small leak occurs from the valve it can be stopped by operating the lever handle several times.

2.4.4 Opening up and maintenance In principle, the breather valve is removed during dry-docking work, inspected and maintained. However, as part of intermediate maintenance, it should be opened up, the soot and rust removed and the valve seat should be inspected for scratches and other damage by penetration checks. If scratches are detected, then the contact surfaces should be faced. If scratches or deterioration on the diaphragm is observed, it should be replaced by a spare diaphragm. Generally, a breather valve is not supplied as spares. Therefore the breather valve cannot be replaced by a spare one. In this case, a blind plate should be inserted in the flange during maintenance and the tank pressure should be controlled appropriately.

2.4.5 Maintenance period Other than an emergency such as a leak in the breather valve, the maintenance of this valve should preferably be carried out during the outward voyage (during ballast voyage) when the tank pressure is comparatively steady.


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3. Inspection and maintenance of P/V breaker


3.1 General (see Fig. N-4-4) The P/V breaker is a safety device installed in addition to the breather valve for preventing damage to the cargo tank. The pressure settings of the P/V breaker are slightly higher than that of the breather valve. They are 18 kPa /-7 kPa (about 1,800 mmAq/-799 mmAq). The breaker activates when the negative or positive pressure in the tank becomes excessively high because of defective activation of the breather valve or clogging of the flame screen. To ensure that the safety device activate correctly, the level of fresh water sealed in the P/V breaker or the level of the mixture of antifreeze solution and fresh water should be checked and adjusted to the required level. The sight glass should be cleaned and the scale should be marked distinctly during the maintenance so that accurate pressure (water level) readings can be taken.

3.2 Water level inspection

3.2.1 Inspection procedure If the water level of the P/V breaker is not correct, the breaker may activate at unexpected tank pressures. The water level should be inspected according to the procedure described below.

1) Check the tank pressure. The time required for inspecting the water level is about 1 hour, therefore,

adjust the tank pressure beforehand so that the gas required for adjusting the tank pressure is not released during the work.

2) Fully open the IG branch valve of each tank. 3) Fully open the vent riser valve, release the IG main line pressure and make the pressure in the P/V

breaker equal to the atmospheric pressure.

4) Read the water level from the reference point (zero point) corresponding to the specific gravity of

the liquid sealed in the P/V breaker and adjust the level. Generally, water is replenished for adjusting the level (fresh water or a mixture of fresh water and antifreeze solution).

5) After adjusting the water level, fully close the vent riser valve. 6) Gradually open the IG branch valve of each tank until it is fully open. 7) Read the water level and tally the reading with the readings indicated by the tank pressure indicator

in the CCR and bridge.

3.2.2 Confirming the results of the inspection If the results of the inspection show that the water level is not correct for the reference point corresponding to the specific gravity of the liquid, then further adjustments are necessary. In summer, the seal water vaporizes rapidly and in one voyage the change in the water level may be as much as 1 kPa (about 100 mmAq). Thus, extreme care is required in summer.

The vent riser valve should be kept fully open until the water level adjustment of the P/V breaker is completed.



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Fig. N-4-4 P/V Breaker


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3.3 Water level adjustments Consider the points below when adjusting the water level.

3.3.1 Reference point (zero point) The reference point corresponding to the specific gravity of the sealed liquid is as given below.

1) Specific gravity 1.00, fresh water 2) Specific gravity 1.037, fresh water 70%, antifreeze solution (ethylene glycol) 30% 3) Specific gravity 1.05, fresh water 60%, antifreeze solution 40%

3.3.2 Freezing temperature (antifreeze solution: ethylene glycol)

1) Specific gravity 1.037, fresh water 70%, antifreeze solution 30%, freezing temperature: -16°C 2) Specific gravity 1.05, fresh water 60%, antifreeze solution 40%, freezing temperature: -25°C

3.3.3 Volume at reference point and mixing of antifreeze solution

1) The volume at each reference point should be calculated. Calculate the volume from documents provided by the shipbuilder or remove the solution from the P/V breaker and actually measure it. 2) From the volume at the reference point, determine the respective quantities in the mixture.

3) Display the reference point (mixing ratio) used at an easily visible location on the P/V breaker.

3.4 Maintenance

3.4.1 Maintenance period Several hours may be required for cleaning and maintenance of internal parts of the P/V breaker depending on the work to be done. From the aspects of safety, this work should be implemented during the outward voyage as far as possible. However, this work can also be performed during the homeward loading voyage. In such case, the tank pressure should be monitored carefully during the work.

Example: TAKASUZU (Built by MHI in the year 2000) Specific gravity: 1.037, volume at reference point: 289.3 L, fresh water: 202.51 L, antifreeze solution: 86.79 L Specific gravity: 1.05, volume at reference point: 286.8 L, fresh water: 172.08 L, antifreeze solution: 114.72 L


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4. Inspection and maintenance of hydraulically operated valves and hydraulic system


4.1 Functional test of hydraulic valves

4.1.1 Implementation period The functional test should be carried out at an appropriate period before entering the loading port or the discharging port. However, tests of tank valves should be not being carried out during the loading voyage to avoid contamination of the cargo oil. Accordingly, only valves that pose no risk of cargo oil contamination should be tested during the loading voyage. Valves in lines that are expected to be filled with oil for disposal of remaining oil should be tested before the ballast voyage.

4.1.2 Test procedure Implement the test procedure described below according to the record sheets for testing hydraulic valves (prepared at each voyage to suit the valve arrangement). (See Fig. N-4-5.)

1) Start the hydraulic pump for operating the valve. (Check the oil level in the storage tank.) 2) Station an adequate number of crew in the CCR, valve control room and local valve stand on the

deck. (A group of two persons for checking the closing/opening of valve and for valve operations.) 3) After confirming the valve number, measure the time required to open/shut (fully open fully

closed) the valve by a flow meter type valve position indicator or valve position transmitter using a stop watch.

4) The test on valves remotely operated (excluding opening valves) from the CCR console should be performed while communicating with the personnel on site using transceivers.

5) Solenoid valves and hydraulic pipes should be checked for abnormal noise and leaks. 6) If an abnormality is detected in the open/shut time of the valves, the cause should be investigated

and the open/shut speed should be adjusted by the method described below.



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Fig. N-4-5 Example of record sheet for testing hydraulic valves


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4.2 Adjusting the open/shut speed of valves

4.2.1 Setting standards The manufacturer's recommendation of time settings for each valve should be followed when performing the adjustments. Generally, the standard time for 1-inch diameter valves is about 2 seconds. However, the minimum time should be taken as 10 seconds even for small diameter valves. To reduce pressure surge in gate valves, adjustments should be made such that the valve closing time becomes 60 or more seconds, where possible. For details of the standards, refer to the "Standards for open/shut speed of hydraulic butterfly valves" (Fig. N-4-6).

4.2.2 Adjustment method The operation of the butterfly valve deteriorates with the passage of time due to changes in flow rate in the hydraulic circuit, inclusion of air and heating or cooling of outside air (change in viscosity of operating oil). Therefore, the valve open/shut speed needs to be adjusted. The adjustment method is given below.

1) The open/shut speed of the valve is adjusted by adjusting the flow rate by the opening of the needle valve (flow control valve) provided at the locations given below. (See Fig. N-4-7.)

(1) Manually operated 4-way valve (2) Pilot operated 4-way valve (3) Solenoid valve

2) The needle valve can be fully closed by loosening the lock nut and rotating the needle valve in the clockwise direction. The flow rate becomes "zero" and the hydraulically drive valve stops. If the valve is rotated in the counterclockwise direction, the flow rate increases and the open/shut speed increases.

3) After adjusting the speed setting, always tighten the lock nut and lock the valve.


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Standards for open/shut speed of hydraulic butterfly valves

Valve Diameter

MM Inch

Standard speed（sec） Allowable range（sec） Remarks

80 3 10 8 – 12 100 4 10 8 – 12 150 6 10 8 – 12 200 8 12 10 – 16 250 10 15 13 – 20 300 12 18 16 – 24 350 14 21 18 – 28 400 16 24 22 – 32 450 18 27 24 – 36 500 20 30 27 – 40 550 22 33 30 – 44 600 24 36 33 – 48 650 26 39 35 – 52 700 28 42 38 – 56 750 30 45 41 – 60 800 32 48 43 – 64

1)Above is shown standard speed of ordinary butterfly valve operation but it is excepted that if it is specified in design drawing of the valve.

2)For ballast pump delivery valve, do not set speed less than 20 second If the diameter Is less than 300mm. 3)Do not set speed of delivery valve for tank cleaning main line less than 60 second. 4)Do not set speed of manifold gate valve less than 60 second.

Fig. N-4-6 Standards for open/shut speed of hydraulic butterfly valves


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Fig. N-4-7 Needle valve (Flow control valve)


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4.3 Replacement of seat ring of butterfly valve (See Fig. N-4-8)

If the valve seat ring is damaged and leakage occurs, safety measures such as gas freeing should be adopted and the seat ring should be replaced according to the procedure given below. Before starting the replacement work, always confirm that a spare seat ring is available. Also, study the piping arrangement thoroughly, and start the work only after setting the pressure of the tank connected to the piping to zero.

1) Completely seal the remote controlled valve and display a warning so that it is not operated by mistake during the replacement work. Confirm that the valve is closed.

2) Close the hydraulic main valve and relieve pressure in the hydraulic piping. (If necessary, close the needle valve also.)

3) Remove the hydraulic piping connected to the actuator. Cover the removed hydraulic piping so that no dust or other foreign matter enters it.

4) Remove the valve unit using hoisting equipment such as wire and chain blocks. However, if an appropriate eye plate for hoisting the valve is not available in the vicinity, be sure to assemble a adequate scaffolding (or a tripod) and then remove the valve.

5) If the flange fitted to the valve unit cannot be removed, fit an eye bolt to the pipe flange on one side, pull the valve in the opposite direction using a chain block or other means to create a clearance between the flanges, and then try to remove the valve. (If a hydraulic jack is available, then it can be used.)

6) Remove the seat ring bolts and then remove the seat ring. (After removing the seat ring bolts, strike the rear side with the hammer shank lightly ensuring that no scratches are caused. This action will displace the seat ring so that it can be easily removed.)

7) Clean the contact surface of the seat ring. (Clean using petrol.) 8) Fit the new seat ring and check its seating condition. 9) Hoist it again, place between the flanges and re-seat it. 10) Tighten the bolts and secure the flange to the valve unit. 11) Tighten the bolts at diagonal locations temporarily first and then fully tighten them. 12) Fit the hydraulic piping, bleed out the air in the piping and then carry out the functional test of the

valve.


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Fig. N-4-8 Seat ring replacement work


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4.4 Bleeding out air from the hydraulic piping

4.4.1 Inspection If the air in the hydraulic piping has not been bled out adequately, abnormal noise generally occurs during operation of solenoid valve. The phenomena mentioned below may occur in the flowmeter type valve position indicator and the valve position transmitter. In these cases, air bleeding work is necessary.

1) The pointer instantaneously swings out when the valve is operated. 2) The pointer does not swing smoothly when the valve is operating 3) Regardless of whether the valve is fully open or fully closed, the lamp in the valve position

indicator on the CCR console does not stop flickering.

4.4.2 Air bleed procedure Connect the hydraulic hand pump to the self-sealing coupling in the hydraulic unit (solenoid valve, etc.) from which air is to be bled. On the other hand, air purge and pressure release valve unit is to be connected to the self-sealing coupling (plug type) of the actuator on the valve side. Connect a plastic hose to the plug of the air bleed valve and keep an oil receiving can or drum ready. Open the air bleed valve on the return side of the hydraulic actuator while repeatedly opening/closing the valve using the hydraulic air pump and bleed out the air in the hydraulic piping. If air is included in the hydraulic piping, milky white operating oil can be observed coming out of the air bleed valve. Open and close the valve repeatedly until air is bled out completely and transparent operating oil comes out of the air bleed valve.

* Air purge and pressure release valve unit

As shown in Fig. N-4-9, the air purge and pressure draw valve unit consists of an air purge valve assembled on the threaded part of the socket-type self-sealing coupling, and is stored in the spares box.


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①Self seal coupling（Socket Type）

②Air purge valve

“This unit is stored in a spare parts box”

Fig. N-4-9 Air purge and pressure release valve unit


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4.5 Inspecting the operating oil

4.5.1 Inspecting the oil quantity and replenishing oil Inspect the quantity of oil in the storage tank periodically and at the start of each hydraulic pump operation. If the oil level has dropped abnormally, there is probably a leak from the hydraulic line or from the hydraulic equipment. Find the leakage location as quickly as possible and adopt measures to prevent leaks by repairs or by other means. If the operating oil has been drained out for carrying out repairs or inspection work, replenish operating oil up to the required level. However, the oil level in the storage tank varies when the system is in operation and when it is at a stop. When replenishing the oil, especially in summer, take adequate care against overflow.

4.5.2 Inspection of strainer and cleaning of storage tank The operating oil of the hydraulic valve is used for opening/closing the valve. If foreign matter gets mixed up with this oil, abnormalities may occur such as clogging of the orifice or constraints on the free movement of the spool of the solenoid valve. Thus, the strainer should be inspected and the storage tank for the operating oil should be cleaned. Water may also accumulate in the storage tank due to changes in the outside temperature. This water should be removed through the drain cock periodically.

4.5.3 Analysis of properties by shore testing organization Water or moisture is the cause of mold or corrosion, which can clog the system's strainers. Or, the operating oil may deteriorate excessively. Once a year the operating oil should be sent to a shore testing organization for analysis of its properties. A sample of about 1 liter of oil should be taken from the sump tank or from the air bleed of the actuator in a special container and sent to the organization for analysis.

* Removal of foreign matter in a newly built ship

Before filling operating oil in a newly built ship, the hydraulic lines and the systems are blown with nitrogen gas for removing impurities and water. This work is performed in the presence of the manufacturer. If the foreign matter is not completely blown away, various kinds of problems could occur.

4.6 Inspection of accumulator

4.6.1 N2 gas charge pressure setting The accumulator is charged with N2 gas for maintaining the operating pressure in the hydraulic circuit, using the compressibility of gaseous body. The minimum pressure of the hydraulic circuit of 80% ± 2 kg/cm2 is considered to be the appropriate initial N2 gas charge pressure setting. At operating pressures of 7.8 MPa (80 kg/cm2) to 8.8 MPa (90 kg/cm2), the pressure of nitrogen gas charged in the accumulator is 6.9 MPa (70 kg/cm2), and at operating pressures of 4.9 MPa (50 kg/cm2) to 5.9 MPa (60 kg/cm2), the corresponding pressure is about 3.9 MPa (40 kg/cm2).

4.6.2 Inspection Inspection should be carried out periodically (once every six months) to confirm that the charging pressure lies in the prescribed range of pressures. If the pressure has dropped, the gas should be adequately replenished from a spare N2 gas container.

4.6.3 Measures when the N2 gas charging pressure drops Problems may arise such as the operating pressure of the hydraulic circuit may not be maintained if the N2 gas charging pressure drops or the bladder in the accumulator is ruptured. This abnormality can be detected since the hydraulic pump repeatedly loads/unloads around the designated pressure even when the valve is not operated. As a measure against this problem, the nitrogen gas should be charged or the bladder in the accumulator should be renewed. This action is also observed when the predetermined pressure for loading/unloading is abnormal.


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4.7 Inspection of hydraulic hand pump

4.7.1 Construction The hydraulic hand pump consists of the main unit and two rubber hoses. The main unit has a hand-operated piston pump on top of a small oil tank, a relief valve, pressure gauge and two self-sealing couplings.

4.7.2 Functional check Since this pump will always be used in an emergency, the items mentioned below should be checked before each voyage and before entering the port and the pump operation should be confirmed.

1) Confirm that the operating oil in the reservoir is filled to the reference oil level. If not, replenish

operating oil. 2) Operate the hand pump, and confirm that the oil pressure rises and the relief valve activates at 90

kg/cm2. 3) The pressure setting of the relief valve can be set arbitrarily to some extent. If the opening/closing

of the valve is difficult at 90 kg/cm2, you may turn the adjustment handle of the relief valve in the clockwise direction, raise the relief pressure setting and set a higher pressure. However, note that the hand pump is designed to withstand a pressure of 105 kg/cm2.

4) The hand pump on the upper deck is generally provided with a trolley for transporting the pump. The rotating parts of the trolley should be oiled so that they do not become rusty.

(Refer to "3.7 Failure of hydraulic valve and hydraulic system" on P3-31 of the "Discharging Section.")


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5. Measurement procedure, inspection and maintenance of gas detector Click here to view video – 100.mp4

5.1 Detectors provided on tankers Detectors provided on tankers are generally of two kinds: portable gas detectors and fixed gas detectors.

1) Portable gas detectors a) Catalytic combustion type combustible gas detector b) Thermionic detector type combustible gas detector c) Optical interferometric type combustible gas detector d) H2S gas detector e) Chemical type gas detector (Kitagawa type detector, Drager type detector, etc.) f) Oxygen concentration detector g) Infrared (non-dispersive type) detector

h) Personal gas watch & oxygen monitor

2) Fixed gas detectors Fixed type combustible gas detecting equipment (catalytic combustion type, infrared type)

5.2 Condition during gas measurement

5.2.1 Inert condition During normal voyages of tankers, an inert condition is maintained in the cargo tanks. Inert condition refers to the condition in which the oxygen concentration of the entire environment within the tank is below 8% by volume. The IGS should be adjusted such that the inert gas supplied by it is less than 5% by volume.

5.2.2 Non-inert condition Non-inert condition may be interpreted as the two conditions below.

1) The entire cargo tank or a part thereof has been gas freed for dry-docking, repairs or other

inspections, and the oxygen concentration of the said tank is 21% by volume. 2) The oxygen concentration within the cargo tank is greater than 8% by volume.

5.3 Gases measured In crude oil tankers, there are no spaces that are replaced by special gases generally. Thus the gases to be measured are mainly hydrocarbon gases, hydrogen sulfide, carbon monoxide and oxygen.

5.3.1 Measurement of oxygen concentration Oxygen concentration is generally measured and confirmed as given below.

1) Confirm the inert condition in the cargo tank at discharging/loading port. (less than 8% by volume) 2) Confirm the oxygen concentration in the cargo tank before crude oil washing. (less than 8% by

volume) 3) Confirm the oxygen concentration before entering enclosed spaces. (21% by volume) 4) Measure the concentration of supplied inert gas. (less than 5% by volume) 5) Confirm the oxygen concentration before entering the CO2 bottle room. (21% by volume) 6) Confirm the oxygen concentration in tank when the gas freeing work. (21% by volume) 7) Confirm the oxygen concentration in the cargo tank when the ship is dry-docked. (21% by volume)

5.3.2 Measurement of hydrocarbon gases Depending on the condition of the hydrocarbon gases, they are to be measured and confirmed as described below.



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1) Measurement of hydrocarbon gases in the inert condition (% by volume) Gas purging by inert gas before airing as a measure to prevent explosion and combustion. (below 2% by volume). To prevent the mixture of gases in the cargo tank from reaching the combustible range during the gas freeing work, gas purging should be carried out using inert gas before airing using fresh air and the concentration of hydrocarbon gases should be brought down below 2% by volume. 2) Measure the concentration of hydrocarbon gases (% LEL) in atmosphere at an oxygen

concentration of 21% by volume. a) Measure the concentration of hydrocarbon gases before internal inspection of tank. (below 2%

LEL) However, if the inspection in the tank for less than 1 hour, a value below 5 % LEL is acceptable.

b) Measure the concentration of hydrocarbon gases before entering the pump room. (below 1 % LEL)

c) Measure the concentration of hydrocarbon gases before entering the ballast tank. Confirm that the concentration of hydrocarbon gases is zero. d) Confirm that the concentration of hydrocarbon gases is zero before entering enclosed spaces. e) Confirm that the concentration of hydrocarbon gases is zero before entering accommodation

spaces.

5.3.3 Measurement of hydrogen sulfide (H2S; ppm) Measure and confirm the concentration of H2S as given below.

1) Measure the concentration of H2S before entering the cargo tank. (less than 10 ppm) (0 ppm) 2) Measure the concentration of H2S before entering the pump room. (less than 10 ppm) (0 ppm) 3) If the concentration of hydrocarbon gases has been measured in the ballast tank, and if necessary,

the concentration of H2S should be measured. 4) If hydrocarbon gases are expected to have entered into enclosed spaces, or if the concentration of

hydrocarbon gases have been measured, measure the concentration of H2S. 5) If the ballast tanks and enclosed spaces have been aired, measure the concentration of H2S at two

locations of the exhaust ports. 6) Measure the concentration in the work spaces when the arm/hose is connected or disconnected in

the manifold.

7) Measure the concentration of carbon monoxide (below 50 ppm)

5.4 Gas measurement procedure

5.4.1 Measurement procedure in the inert condition The measurement is mainly performed during the gas freeing work of the cargo tank. A typical example of measurement is during the HC gas purging (target value: less than 2% by volume) before airing. This is a measure to prevent explosion/combustion.

1) Measure the oxygen concentration in the tank. 2) During a normal voyage the oxygen concentration in the tank is less than 8% by volume, therefore

gas concentration cannot be measured at %LEL range. 3) For measurement in terms of %LEL, the oxygen concentration should necessarily be greater than

13% by volume. Accordingly, for gas measurement in the cargo tank during a normal voyage, the measurement should be in % by volume. However, in an infrared system, measurement is possible in %LEL even in the inert condition. 4) For measurement in % by volume, the heat conduction system and the infrared system may be

used. 5) The measurement in % by volume is mainly performed during the gas freeing work of the cargo

tank. A typical example of measurement is during the HC gas purging (target value: less than 2% by volume) before airing. This is a measure to prevent explosion/combustion.

Even if the concentration of oxygen is more than 21% by volume, separate precautions need to be taken against toxic


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6) The orange-colored tube is used in the measurements in terms of the volume scale.

5.4.2 Measurement procedure in the non-inert condition The main objective is inspection before gas freeing work and entry into ballast tank and enclosed spaces. This is to ensure safety of life.

1) Measure the oxygen concentration in the tank. 2) The results of the measurement should indicate an oxygen concentration in the tank of 21% by

volume. 3) The concentration of hydrocarbon gases in the tank can be measured in terms of %LEL. 4) Catalytic combustion type combustible gas detector can be used as the gas detector. 5) Measure the low concentration toxic gases. This includes mainly H2S and carbon monoxide. 6) Measure the H2S concentration using the H2S gas detector. When entering the cargo tank and the pump room, carry the watch type portable H2S and oxygen concentration detector. (Watch Type gas monitor: GAS WATCH HX-GW (H2S/O2) RIKEN KEIKI CO.,LTD.) 7) In tankers where inert gases are used to maintain inactive condition in tank to prevent

explosion/combustion , precautions against carbon monoxide are necessary. 8) For measurement of carbon monoxide, a chemical type gas detector may be used. Detectors generally used are Kitagawa-type detectors and Drager-type detectors.

9) The main objective of measurement in the non-inert condition is inspection before gas freeing work

and entry into ballast tank and enclosed spaces. This is to ensure safety of life. 10) The green-colored tube is used in measurements in terms of the LEL scale.

5.4.3 Proper use of sampling tube The sampling tube for portable gas detector is made of a material that adsorbs very little gas. However, if it is not used properly, it may hinder zero adjustments and indicator accuracy. Combustible gases may stick to the inside surface of tubes used in highly concentrated combustible gas, and correct values cannot be measured in low-concentration combustible gases, therefore, the tubes are distinguished by color and used.

1) The orange-colored tube is used in measurements in terms of the volume scale. 2) The green-colored tube is used in measurements in terms of the LEL scale.

5.5 Inspection and maintenance of gas detectors Efforts should be made to inspect and maintain items relevant to gas detectors after referring to the detailed instruction manuals of the manufacturer, and to obtain accurate measurement values.

5.5.1 Hydrocarbon gases (Riken portable HC meter "NP-237H)

1) Before using the device, confirm that there is not damage to the measuring unit, particularly no

cracks on the meter window and that the pointer of the meter indicates zero. 2) Check points of filter tube with flow monitor a) Are there any cracks have an influence to gas suction?

Chemical type gas detectors use chemical detector tubes specific to the gas to be detected. It should be noted that detector tubes have an effective lifetime.

* Gases and spaces in which fixed type gas detectors are used The fixed type gas detector can be used for 24-hour monitoring of gases. a) Measurement of concentration of hydrocarbon gases in the pump room b) Measurement of concentration of hydrocarbon gases in the ballast tank c) Measurement of concentration of hydrocarbon gases in the accommodation spaces d) Measurement of oxygen concentration in the pump room and ballast tank


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b) Is the internal cotton wool filter dirty? c) Have drops of water accumulated? d) Are the caps with nipples at both ends loose?

3) Check points of gas sampling tube (30 m) a) Is the tube bent? Is it twisted? Is the hole blocked? b) Is the snap-on coupling for connecting the tube end to the main unit fitted properly to the tube?

4) After changing over the selector switch to 100% by volume or 20% by volume, draw in fresh air from the atmosphere for about 10 minutes.

5) After changing over the selector switch to 100% LEL or 20% LEL, draw in fresh air from the atmosphere for about 5 minutes.

6) Two minutes after locking the gas sampling tube at the position to be measured, read the indication on the meter scale corresponding to the measurement range of the selector switch.

7) For measurements in %LEL, the oxygen concentration should necessarily be greater than 13% by volume.

8) Replace the cotton wool in the air filter before the measurement. 9) Adjust the gas sensitivity (span) once in every two months.

5.5.2 Oxygen meter (Riken OX-226/OX-227) 1) If the meter is to be used at a location with a very different environmental temperature, wait until

the meter gets adequately acclimatized to that temperature (about 10 minutes) and then re-adjust the span.

2) When measuring the oxygen concentration in inert gas, if the concentration of carbon dioxide is greater than 15%, the life of the sensor may decrease.

The concentration of carbon dioxide can be measured with chemical type gas detector (Kitagawa type, Drager type, etc.) 3) The life of a sensor is about 1 year. If the phenomena mentioned below are observed, the sensor

needs to be replaced. a) Even after turning the span adjustment knob, the concentration cannot be adjusted to 21%. b) If the meter indication is unsteady.

4) The filter should be inspected once a month. It should be replaced if dirty.

5.5.3 H2S monitor (Riken HS-82) 1) Calibrate the gas sensitivity once in 2 to 3 months. Perform the calibration of gas sensitivity using a

gas calibration kit specially provided with the monitor. 2) After calibration, if the indication does not match the calibrated gas concentration value, replace the

sensor. 3) The constant potential electrolysis method is used by the monitor. If the battery voltage is

inadequate and the battery is left as-is without charging, then about 15 hours of wait time are necessary after replacing with a new battery.

4) If a gas calibration kit is not available, request the manufacturer for the same.

5.5.4 Chemical type gas detectors (Drager-type) 1) Perform the air tightness test for 1 minute using the unopened Drager-type detector. 2) It should be noted that detectors have an effective lifetime. 3) Use detectors that are appropriate for the gas to be measured.

(1) For % by volume measurements, use standard gas (orange-colored label). (2) For % LEL measurements, use standard gas (green-colored label).


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6. Functional test of bilge alarm


6.1 Implementation period The functional test should be carried out (1 to 3 days before) before entering the loading/discharging port. Generally, this test is performed simultaneously with the line pressure test or the operational test of the valve.

6.2 Procedure for implementing the functional test Bilge sensors of two kinds are mainly used: float-type and electrode-type sensors (there may be ships that use pressure-detecting sensors also). The procedure for implementing the alarm test may differ slightly depending on the kind of sensor used. Here, the procedure for float-type and electrode-type sensor is described.

6.2.1 Float-type bilge sensor Generally two float-type bilge sensors are installed in the pump room. The alarm test can be carried out without using any testing equipment. The float merely has to be lifted to perform the test. Personnel should be stationed in the pump room and the CCR during the test.

6.2.2 Electrode-type bilge sensor Generally one electrode-type bilge sensor is installed in the pump room. The test is performed by bringing the sensor in contact with water filled in a bucket. Compared to the float-type sensor, the test requires some additional work. Personnel should be stationed in the pump room and the CCR during the test.



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7. Functional test of high high level alarm


7.1 Implementation period The functional test of high-high level alarm installed in the cargo tank should be performed before the ship enters the loading port. The results of the test should be recorded.

7.2 Procedure for implementing the functional test

7.2.1 Independent high high level alarm As shown in Fig. N-4-10, the float can be lifted by pulling up the test rod on site and the activation of the alarm can be checked in the CCR.

7.2.2 Alarm on the tank level gauge Generally, the test of the alarm on the tank level gauge is performed using the changes in level of the tank during loading/discharging. The ullage level of the tank at the instant when high level and low level alarm sounds is recorded after confirming that the alarm works correctly.

7.3 Setting values The high high level alarm is also called the overflow alarm. It consists of a magnetic float-type alarm sensor installed at an independent position separate from the high level alarm attached to the tank level gauge. The alarm setting values are as given below.

1) High high level alarm: 98% of the total capacity of tank 2) High level alarm attached to tank level gauge: 95% of the total capacity of tank



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①Take out cap nut by spanner.

②Pull up test rod inside fully

③Float is move up as shown above ③, then activate alarm.

Fig. N-4-10 Procedure for implementing the functional test of high high level alarm


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8. Sea chest valve leak test


8.1 Implementation period The leak test should be performed before the ship reaches the loading/discharging port. It is recommended that the test using air pressure be carried out in sea areas with calm water conditions either at anchorage or when the ship is drifting.

8.2 Test procedure

8.2.1 Leak confirmation method (shell side) Leaks in the sea chest valve can be judged by opening/closing the drain valve installed between the sea chest valve (shell side) and the blind plate. If a pressure gauge has been permanently installed, the leak can be detected from the changes in pressure indicated by the gauge.

8.2.2 Test by air pressure The test should be carried out once per voyage at a pressure not exceeding 0.34 MPa (about 3.5 kg/cm2). The implementation procedure is as given below. (See Fig. N-4-11.)

1) Review the piping system and install fittings "A" and "B" if connections do not already exist.

Fitting B should be on the bottom of the pipe at the lowest point between the sea valve and block valve 2 to allow for draining.

2) Close the sea chest valve and the block valve 2. 3) Drain water from section of pipe between the sea chest valve and block valve 2. 4) Close the inboard sea valve (block valve 1). 5) Pressurize pipe to approximately 0.34 MPa. 6) Monitor the pressure drop over 15 minutes. 7) If the pressure drops, check alongside the ship for bubbles of air escaping through the sea chest

valve. Also check at test fitting B for leakage, If necessary using a balloon over the fitting to test for slow leaks.

8) If the inboard and outboard sea valves are tight, block valve 2 may be tested by opening the inboard sea valve and closing the test fitting B. The line should be re-pressurized to about 0.34 MPa and the pressure drop observed over 15 minutes.

Note: Care must be taken that the pipe system is not over pressurise during the test. This can be done by utilizing a pressure limiting device on the air inlet set for no more than 0.34 MPa.



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Fig. N-4-11 Procedure for implementing sea chest valve test

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