Main engine exhaust valve
Sub Topics:
Hydraulic valve actuator
Exhaust valve assembly
Air spring Cylinder of the Exhaust valve
Valve Rotation
Hydraulic sheathed Pipe
Construction and Working
Hydraulic valve actuator:
(a) Exhaust valves actuated by means of a Push Rod and Rocker Arm Unit face a problem of absence of true axial force on valve stem during operation. The operation results in excess wear between the valve stem and its bushing because of the side thrust exerted by pushrod on the valve stem during the opening.
(b) Hydraulic actuator overcomes the above problem. A piston is fitted on the top of the valve stem inside a hydraulic cylinder, Piston operates by means of an actuator pump unit through high pressure sheathed pipe,
(c) A pair of piston rings, provides sealing in the open-bottomed hydraulic cylinder. An oil bleed valve located at the top of the hydraulic cylinder allows a controlled amount of oil to pass to the air cylinder located below the hydraulic cylinder for lubrication.
(d) The camshaft driven actuator pump delivers oil to the valve to open so that on the download stroke oil returns to the actuator pump cylinder as there is no delivery valve in the pump discharge line that allows the valve to close under the action of the closing mechanism.
(e) A relief valve is located at the top of the pump cylinder.
(f) A makeup oil connection is located just above the top of the pump piston to ensure full oil discharge during downward stroke.
(g) A puncture valve on the actuator pump may be actuated to release some pressure to delay exhaust valve opening when starting the engine in Astern direction to ensure full starting air effect.
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Valve Assembly:
(a) Cage type valves comprise the water-cooled body, detachable seat, valve, spring unit and valve drive.
(b) The single valve is located in the centre of the cylinder cover and connected to it by means of four or more studs and hydraulically tightened nuts. The valve cage form a gas-tight seal with a cylinder cover with mild steel or soft iron ring.
(c) Valve cage is made of cast iron as it is not subjected to mechanical/thermal loading.
(d) Detachable seat of molybdenum steel is able to resist thermal/corrosive environment and can easily be machined.
(e) Seat area generally incorporates an insert of stellite material (hard alloy) is expensive but has good corrosion and damage resistance at high temperature.
(f) Valve spindle guide (bush) of bronze fitted in the valve body.
(g) Spindle can be made up of the following combinations:
-Austenitic material with stellite facing on the seat and a coated stem [chrome coated (phasing out due to environmental reasons) or cermet].
- Two-part Austenitic stem as above but with a Nimonic head and no insert on the seat [Nimonic -Nickel-based alloy are wear and corrosion resistance at high temperature].
-A one-piece Nimonic valve with no stellite insert.
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Air Spring Cylinder:
Some positive force is needed to ensure the valve closes after the rocker or hydraulic opening force is removed.
(a) Coil springs strength had to be sufficient to ensure that the rocker push rod follower remained in contact with its cam at all times to avoid impact damage. coil springs are subjected to fatigue failure. Cause rubbing wears at the contact face at the valve body and spring cover. Provide a frictional contact between the valve body and valve steam which prevents valve rotation.
(b) Air Spring: A piston is fitted to the valve stem below the hydraulic cylinder and this piston reciprocates in a cylinder compressing the air in the cylinder when the valve opens. This compressed air acts on the piston to close the valve when the upcoming hydraulic force is removed. Air leakage from the cylinder is made up by using an air supply at a pressure of 5 bar through a non-return valve.
(c) The area of the piston is calculated to ensure the correct closing force. The space above the piston is vented to ensure no opposing force.
(d) Lubrication of the cylinder wall by controlled leakage of hydraulic oil from the hydraulic cylinder.
(e) Sealing air to the gland contains oil mist in order to limit wear at the seal and valve stem.
(f) At the top of the casing, a spring-loaded check rod passes through a bush and has contact with the groove in the air piston. It indicates valve opening and also valve rotation as it is re-seats.
Valve Rotation:
(a) When residual fuel is burned it produces a number of damaging products including Vanadium pentaoxide slag which is corrosive and solidified, can cause damage to the valve face and seat. If the valve is allowed to rotate slightly as it closes a light grinding effect is produced at the faces and these deposits are removed.
(b) By valve rotation local overheating is avoided (which may be because of a defective fuel injector).
(c) A Rotocap device is not practical for a large low-speed engine as it produces a set angle of rotation when the valve is opening.
(d) The "Spinning Rotation" effect is brought by the action of exhaust gas on vanes or spinners fitted on the valve spindle. When the exhaust valve opens the escaping exhaust gas acts on the spinners produces rotation if no frictional contract exists. If coil springs are used, so replaced by "Air Spring".
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Hydraulic Sheathed Pipe:
Leakage from the high-pressure pipe can result in a hydraulic oil fire because of spray on the Exhaust Manifold. The Safeguard to the above is that the HP pipe is surrounded by a braided steel pipe with a narrow gap.
Failure of the HP pipe will result in the defective operation of the exhaust valve with poor cylinder performance. Leaking oil drains through a small hole in the actuator pump body into the cam box.
Overhauling
(A) State the circumstances owing to which it may be necessary to renew an exhaust valve.
- Service life of the exhaust has been completed. Using the valves above the service life as prescribed by the manufacturer will result in loss of strength of valve material and ultimately result in fatigue failure of the material.
- Excessive burnt, corrosion, erosion, pitting on the face of the valve, cracks on the valve, bend spindle and loss of trueness of spindle will require the valve to be renewed.
- Excessive loss of material at the valve face because of excessive grinding of the valve face.
- Excessive loss of material of spindle due to worn out spindle. This will increase the clearance between guide and spindle. And thus required renewal of the valve.
- Check the following clearances during overhauling of the valve and compare them with the manufacturers recommended limits. If the measured values are beyond the limits the valve should be replaced.
(i) The area between 460 mm and 620 mm, measure from the top of the spindle at four diametrically opposite points on the circumference of the valve spindle with a Vernier calliper.
(ii) Measure the gap between the spindle template and seating of the spindle with a feeler gauge at each point indicated on the templates as notches.
- Excessive burnt, corrosion, erosion, pitting on the face of the valve, cracks on the valve, bend spindle and loss of trueness of spindle will require the valve to be renewed.
- Excessive loss of material at the valve face because of excessive grinding of the valve face.
- Excessive loss of material of spindle due to worn out spindle. This will increase the clearance between guide and spindle. And thus required renewal of the valve.
- Check the following clearances during overhauling of the valve and compare them with the manufacturers recommended limits. If the measured values are beyond the limits the valve should be replaced.
(i) The area between 460 mm and 620 mm, measure from the top of the spindle at four diametrically opposite points on the circumference of the valve spindle with a Vernier calliper.
(ii) Measure the gap between the spindle template and seating of the spindle with a feeler gauge at each point indicated on the templates as notches.
(B) Explain how the exhaust valve is removed and fitted back.
- Stop the main engine
- Block the staring mechanism.
- Shut off the air supply.
- Engage turning Gear.
- Shut off cooling water.
- Shut off the fuel supply.
- Shut off lube oil circulation after 30 minutes.
- Inform bridge.
- Check the maintenance manual for the proper tools and keep them ready
- Check for all the required spare available, keep ready all the o-rings and seal ring spares.
1. Drain the cooling water from the exhaust valve after closing the inlet and outlet valve. Close air supply to the exhaust valve. Dismount high-pressure pipe for the hydraulic valve actuator. Dismount oil return pipe from the exhaust valve. Dismount the cooling water inlet and outlet pipes. Dismount the exhaust pipe ballow.
2. To dismantling the hydraulic nuts, remove the protective caps and use the hydraulic jack and loose the nuts and remove.
3. Before lifting the exhaust valve check that all the connections are removed, attach the crane to the eyebolt at the top of the exhaust valve. Carefully lift the valve and ensure it is clear off the other engine components. Land the exhaust valve on a wooden plate on the platform. Carefully clean the valve bore on the head & recondition the seating and sealing surface of the bore if required. Keep the bore covered and ensure nothing should fall in.
4. Now the overhauling of the exhaust valve can be carried out as per the manufacturer's guidelines. Spindle, seat, guide, air cylinder are calibrated and recorded for reference. Any unusual wear is to be checked with the previous readings. All the components are cleaned, O-rings and sealing rings are renewed.
5. After overhauling and drop-down testing the exhaust valve it is to be fitted back on the cylinder cover. Check inside from the head bore that it is clear. Ensure the seat and sealing surface is properly cleaned.
6. Close the valve with compressed air, lubricate the sealing rings with vaseline and threads of studs with anti-seizure paste. position the valve as per the markings. Mount and tight the hydraulic nut as per the makers prescribed pressure. Mount the pipe connections.
7. Open the cooling water supply and vent the system. open the air supply and check the sealing between the bottom piece and the valve housing.
8. Prepare the engine and inform the bridge for readiness.
- Block the staring mechanism.
- Shut off the air supply.
- Engage turning Gear.
- Shut off cooling water.
- Shut off the fuel supply.
- Shut off lube oil circulation after 30 minutes.
- Inform bridge.
- Check the maintenance manual for the proper tools and keep them ready
- Check for all the required spare available, keep ready all the o-rings and seal ring spares.
1. Drain the cooling water from the exhaust valve after closing the inlet and outlet valve. Close air supply to the exhaust valve. Dismount high-pressure pipe for the hydraulic valve actuator. Dismount oil return pipe from the exhaust valve. Dismount the cooling water inlet and outlet pipes. Dismount the exhaust pipe ballow.
2. To dismantling the hydraulic nuts, remove the protective caps and use the hydraulic jack and loose the nuts and remove.
3. Before lifting the exhaust valve check that all the connections are removed, attach the crane to the eyebolt at the top of the exhaust valve. Carefully lift the valve and ensure it is clear off the other engine components. Land the exhaust valve on a wooden plate on the platform. Carefully clean the valve bore on the head & recondition the seating and sealing surface of the bore if required. Keep the bore covered and ensure nothing should fall in.
4. Now the overhauling of the exhaust valve can be carried out as per the manufacturer's guidelines. Spindle, seat, guide, air cylinder are calibrated and recorded for reference. Any unusual wear is to be checked with the previous readings. All the components are cleaned, O-rings and sealing rings are renewed.
5. After overhauling and drop-down testing the exhaust valve it is to be fitted back on the cylinder cover. Check inside from the head bore that it is clear. Ensure the seat and sealing surface is properly cleaned.
6. Close the valve with compressed air, lubricate the sealing rings with vaseline and threads of studs with anti-seizure paste. position the valve as per the markings. Mount and tight the hydraulic nut as per the makers prescribed pressure. Mount the pipe connections.
7. Open the cooling water supply and vent the system. open the air supply and check the sealing between the bottom piece and the valve housing.
8. Prepare the engine and inform the bridge for readiness.
(c) State the important checks to be made on the engine before and after fitting the exhaust valve.
Before fitting:-
1. Lift up the valve with the engine room crane (Whereby the valve may open) so that drop-down checks can be performed. Connect compressed air to the air cylinder to close the valve: Check with the feeler gauge that there is a clearance between the outer parts of the seating faces of the valve housing and spindle.
2. After shutting off the compressed air supply and releasing the air through the non-return valve on the control unit, the exhaust valve should open. Repeat it a couple of times.
3. Leave the valve closed and shut off the compressed air. If the exhaust valve opens within 15 minutes, check for air leakages around the air spring.
4. Before mounting the valve on the engine, connect the 7 bar working air to the air cylinder to keep the exhaust valve closed during the mounting process. 2. After shutting off the compressed air supply and releasing the air through the non-return valve on the control unit, the exhaust valve should open. Repeat it a couple of times.
3. Leave the valve closed and shut off the compressed air. If the exhaust valve opens within 15 minutes, check for air leakages around the air spring.
5. Mount a new O-ring on the bottom piece and on the bottom of the exhaust valve. Lubricate the O-rings with Vaseline and the threads of the studs with anti-seizure paste.
6. Position the valve in the cylinder cover bore, guiding it in accordance with the exhaust flanges and the guide pin on the exhaust side of the exhaust valve.
Checks after fitting:-
1. Check all the connections are made properly, cooling water is vented, no water leakage is to be found. sealing between the bottom piece and valve housing is checked by opening the air supply.
2. Indicator is engaged on the top of the exhaust valve and the valve is always closed by supplying spring air before opening the hydraulic oil for the actuator.
3. Hydraulic oil to be supplied to the actuator and the system is purged. Connections to be checked for any leakage.
4. Engine to be tried out on air and operation of the valve to be observed with the motion of indicator.
5. unit performance to be taken during the next voyage, recorded and compared.
Overhauling Procedure:
- To overhaul the exhaust valve, place the valve on a wooden platform.
- Loosen the nuts to remove the safety strap and the oil cylinder.
- Discard the O-ring from the air cylinder.
- Remove the four screws from the flange on top of the air piston.
- Take out the flange. Release the safety valve from the air cylinder for the air to escape below the piston.
- Use a tin hammer to loosen the conical locking ring from the air piston. Remove the air piston.
- Lift the valve housing clear off the spindle. Take out the air cylinder. Clean it and check the running surface for wear or possible scores. Measure the diameter of the air cylinder at four points diametrically opposite, using an inside micrometre.
- Remove the screws and dismount the flange of the stuffing box. Remove and discard the O-rings. Inspect the bushing in the spindle guide, for wear. Measure the inside diameter of the air cylinder using an inside micrometre.
- Unscrew and remove the lock screw which holds the bottom piece. Lift the valve housing approximately ten millimetres.
- Take out the valve seat using the tin hammer. Lift the valve housing and place it on a couple of wooden planks. Discard the O-ring from the groove onto the valve seat.
- Loosen the nuts to remove the safety strap and the oil cylinder.
- Discard the O-ring from the air cylinder.
- Remove the four screws from the flange on top of the air piston.
- Take out the flange. Release the safety valve from the air cylinder for the air to escape below the piston.
- Use a tin hammer to loosen the conical locking ring from the air piston. Remove the air piston.
- Lift the valve housing clear off the spindle. Take out the air cylinder. Clean it and check the running surface for wear or possible scores. Measure the diameter of the air cylinder at four points diametrically opposite, using an inside micrometre.
- Remove the screws and dismount the flange of the stuffing box. Remove and discard the O-rings. Inspect the bushing in the spindle guide, for wear. Measure the inside diameter of the air cylinder using an inside micrometre.
- Unscrew and remove the lock screw which holds the bottom piece. Lift the valve housing approximately ten millimetres.
- Take out the valve seat using the tin hammer. Lift the valve housing and place it on a couple of wooden planks. Discard the O-ring from the groove onto the valve seat.
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| Main Engine Exhaust Valve calibration |
Inspect the seating of the bottom piece for damage with a template for damage. Measure the clearance G3 between the template and O-ring groove, using a feeling gauge. Measure the clearance G2 between the template and the valve seat, using a feeling gauge. Take and record the measurements at four diametrically opposite points on the circumference of the valve spindle. Clean the contact faces on the spindle. Measure the gap between the spindle template and the seating of the spindle. Check the burn off F1 of the valve spindle at each of the points A, B, C, D and E. The notches in the spindle template indicate the points.
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| Main Engine Exhaust Valve Spindle calibration |
Check the spindle stem for wear in the area between 460 mm and 620 mm. Measure from the top of the spindle. Take and record the measurements at four diametrically opposite points on the circumference of the valve spindle.
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| Main Engine Exhaust Valve seat calibration |
Check before mounting:
Before mounting an overhauled exhaust valve in the engine, it is recommended that the valve be checked and prepared as follows:
1. Lift up the valve with the engine room crane (Whereby the valve may open).
2. Connect compressed air to the air cylinder to close the valve: Check that a 1.0 mm feeler gauge can be inserted about 15 mm into gap G3, to ensure that there is a clearance between the outer parts of the seating faces of the valve housing and spindle. After shutting off the compressed air supply and releasing the air through the non-return valve on the control unit, the exhaust valve should open. Use a small screwdriver to press the ball into the non-return valve, and cover it with a rag to catch the oil drops. After doing this a couple of times, leave the valve closed and shut off the compressed air. If the exhaust valve opens within 15 minutes, check for air leakages around the air spring.
Check Air piston sealing (air coming out of drain oil hole). Stem sealing (air coming out along spindle stem in exhaust gas duct). Non-return valve for air spring.
3. Before mounting the valve on the engine, connect the 7 bar working air to the air cylinder to keep the exhaust valve closed during the mounting process. Mount a new O-ring on the bottom piece and on the bottom of the exhaust valve. Lubricate the O-rings with Vaseline and the threads of the studs with anti-seizure paste. Position the valve in the cylinder cover bore, guiding it in accordance with the exhaust flanges and the guide pin on the exhaust side of the exhaust valve.
4. Mount the nuts and the hydraulic jacks. Raise the pressure to the value indicated to relieve the system of pressure, remove the hydraulic jacks and high-pressure hoses, and fit the protective caps.
5. Connect the intermediate pipe to the flange at the exhaust valve, mount and tighten the screws. Attach the insulation jacket. Mount the cooling water outlet pipe on the exhaust valve.
6. Mount the high-pressure pipe and the return oil pipe. Open the lube oil supply and the cooling water supply to the exhaust valve. Disconnect the compressed air and connect the normal air supply. The air supply to the exhaust valve must always be connected before turning on the oil supply to the exhaust valve actuator.
7. Check the tightness of the sealing ring between the bottom piece and the exhaust valve housing.
Troubleshooting
Exhaust valve damage due to a bad fuel:
Damage has occurred to the main engine exhaust valves and the fuel supplied at a particular port is suspected.
If it is considered indeed it is a great mistake on the part of the ship's staff. So many other salient points are involved with the composition physical and chemical properties. If the fuel is off-specification the presence of various components and endangers the operation of the machinery.
The fuel was supplied on the basis of type (distillate or residual ) and viscosity (CST) but never mentioned the percentage of Sulphur (low or high), density (kg/meter-cube at measuring temperature in degree cel) and other soluble and insoluble components. It is a great lapse from the supplier too if by mistake the ship's staff mention the grade and type of fuel only. But it is the duty of the supplier to provide all specifications of the fuel oil. Considering this the supplier is also is a great fault by not furnishing the laboratory analysis report, hence the real scenario. As the fuel price is going up, all the companies trying to reduce the running cost, by using low-grade fuels. But if the actual composition is known protective measures can be taken before using the fuel. By using the fuel received at the last port, the exhaust valves of the main propulsion engine are damaged. The exhaust valve in the combustion engine experiences a very complex contact situation of frequent impact, involving micro sliding, high and varying temperature, complex exhaust gas chemistry and possible particulates. In addition, the tribological situation in the exhaust valve system may become even worse due to the presence of some corrosive and chemically active elements. The lack of protective failure is expected to result in increased wear of the contacts surfaces. The fuel oils that are used to run the main propulsion engine also adversely affect the engine parts due to naturally occurring elements present in the F.O. if not burnt efficiently. Corrosion is the primary concern on engine parts when it comes to burning off fuel oil. The corrosion may be categorised into two types 1. cold corrosion and 2. hot corrosion.
Hot corrosion- It occurs due to the presence of vanadium (V) and sodium (Na) in the fuel oil, which affects the exhaust valve and exhaust passage. vanadium is a naturally occurring element in marine fuel oil insoluble form, which means it can not be separated by filtering or through a centrifuge.
Vanadium and sodium combine at an elevated temperature, which takes a crucial role in hot corrosion. The availability of abundant oxygen in the combustion chamber, during the burning of fuel results in the oxidation of V to form VO (oxide) and VO2 (dioxide). During temperature drop, neither further combustion process VO further undergoes an oxidation process to form V2O5 (pentoxide). V2O5, has a low melting point and becomes sticky semi-liquid in nature and adhere to the surfaces they come into contact with. Sodium in the fuel reacts with the water vapour, during combustion to generate NaOH. This in turn combines with SO2, to form sodium sulphate (Na2SO4). Na2SO4 condenses at a temperature below 890°C and will adhere to the surface where already V2O5 is present these resultant deposits block the gas passage and corrode metal surface if the ratio of V: Na =3:1 the resulting complex melting point is at its lowest which is about 350-400° C and there is an increased like the hood of deposit formation. Fuels with high V and Na will increase the temperature for deposit formation in the exhaust passage. At high temperature(>650 deg cel)ash deposit can accelerate corrosion of metal and fouling of exhaust passage.
The second engineer, at first should be issued a letter of protest and compel the supplier to provide the laboratory analysis report. Should make them responsible and liable for any future consequences or damage to the engine parts, as they have failed to provide the particulars of the fuel oil as a statuary requirement by the marine law
.
A. Apart from fuel specification, describe how you, as Second Engineer, should have assisted the owners’ case when receiving the suspect fuel.
A second engineer must emphasise the following points
1.1 MARPOL Annex VI contains requirements that apply to fuel oil used onboard ships. Regulation 14 sets limits on the sulphur content of fuel oil used on board ships, both within designated SOX emission control areas (regulation 14.4) and globally (regulation 14.1). Regulation 18.3 contains requirements that fuel oil delivered to and used onboard ships should not jeopardize the safety of ships or adversely affect the performance of machinery. Regulation 4.2.1.1 of SOLAS II-2 stipulates that except as otherwise permitted, no fuel oil with a flashpoint of less than 60°C shall be used.
1.2 Fuel oil purchasers are responsible for correctly specifying the fuel oil which is to be supplied. It is the responsibility of the supplier to deliver fuel oil that is compliant with the agreed specification and statutory limits.
1.3 These best practices are intended to assist fuel oil suppliers to ensure the quality of fuel oils delivered to ships that are compliant with the agreed specification and statutory limits.
1.4 When developing their procedures, fuel oil suppliers should also consider the guidance provided by existing industry practices and standards, for example, those published by the International Organization for Standardization (ISO).
1.5 This guidance does not apply to the supply of low flashpoint fuels such as LNG, LPG or methyl/ethyl alcohols, nor to pure bio-fuels.
b. Using fuel specifications. Make sure that the specification is communicated to the bunker supplier and properly set out in the charter party.
D. Suggest, with reasons, why particular mention should be made of certain elements that might not be included in the fuel standard.
following are the elements found in the fuel which are unavoidable, they do not contribute to the combustion process but are harmful to the engine and its components. additionally, to remove them extra arrangements are required to make such as purifier, clarifier etc. also they reduce the maintenance period for the engines and made the ship operation costly.
(a) Ash content
(b) vanadium and sodium
(c) calcium content
(d) sulfur content
(e) water content
Additional information regarding bunkering:-
Bunkers and bunkering could give rise to varying disputes between parties to a charter party or bunker supply contract. Disputes relating to bunkers could broadly be divided into three categories: quality disputes, disputes regarding quantity and problems as a result of the bunker supplier’s insolvency.
The quality of fuel may also be a source of concern in terms of compliance with MARPOL Annex VI and stricter sulphur-content regulation.
A dispute on the quality of bunkers may involve the ship-owners, charterer, bunker supplier and/or a possible intermediary, such as a bunker broker.
The quality of bunkers is an important issue for both the ship-owner and the charterer in order to ensure a smooth operation of the ship. In case the bunkers delivered on board are not within specification or otherwise unsuitable for the engine, this may result in severe damage to the vessel. This might in turn lead to delays and substantial consequential losses. Furthermore, arrangements may have to be made to de-bunker, which may be associated with large costs and could also mean deviations from the planned route.
Disputes between Owners and Charterers Under a time charter it is normally the charterer’s obligation to provide and pay for bunkers within a certain specification, which is normally set out in the charter party. However, under e.g. English law the obligation of the charterer goes beyond that: the stemmed bunkers also have to be reasonably fit for the particular vessel’s engines. This naturally implies that the charterer has been made aware of any particular characteristics or requirements of the engine. The ship-owners should thus make sure that the fuel specification is properly and clearly set out in the charter party, by referring to international bunker specification standards and stating special requirements of the engines. It should be noted that the most recent international fuel specifications allow for i.e. higher contents of cat fines than the recommendations of many engine makers. The legal situation under Nordic law is probably similar to the one in England. The requirement as to fitness for purpose may also be expressly included in the bunker clause in the charter party, which is usually the case. The shipowner however bears a heavy burden of proving that the stemmed bunkers were in fact off-spec and that there is a causal link between the poor quality of the bunkers and the machinery damage. Provided the ship-owner is able to lift the burden of proof, the liability imposed on the charterer may be substantial.
Disputes between the bunker purchaser and supplier: - The party responsible for providing for the vessel’s bunkers, either the ship-owners himself or a charterer, enters into a contract for the supply of bunkers on-board. It should be noted that the bunker purchaser’s contracting party is often not the actual fuel supplier. This may give rise to complex legal situations and attempts by the bunker seller to shove the responsibility onto the actual supplier. The bunker supplier usually uses its own standard terms and conditions of sale, which are favourable to the supplier and may be difficult for the buyer to renegotiate. The bunker purchaser should therefore be aware of short-time bars for the notification of a claim (sometimes as short as 7 days after delivery) and limitation of liability clauses contained in the supply contract. The prospects of negotiating amendments to the contract will depend on the buyer’s bargaining position. The bunker supplier has a duty to deliver bunkers within the specified grade of marine fuel and it is therefore important that the bunker order contains an appropriate description of the fuel to be supplied. The selection of a bunker supplier is usually a commercial decision of the shipowner but should be a balancing of quality and price aspects.
If a dispute as to bunker quality arises, the outcome of the dispute will usually be in the favour of the party being able to present the strongest evidence. It is, therefore, crucial to collect sufficient proof of the bunker contents and the incident. Bunker samples are usually drawn in connection with the bunkering and the ship-owners needs to ensure that the samples are representative of the entire delivery. By following the sampling procedures issued by the major fuel quality testing services of Veritas Petroleum Services (VPS) or Lloyd’s FOBAS, bunker purchasers can obtain representative samples which are accepted and signed by the supplier’s representative. It may well be that these are the only reliable samples, as the bunkers may then be mixed with bunkers previously supplied. It is important that the samples are properly sealed and labelled. In case the samples have been taken from the bunker barge and the ship-owners have not been invited to the sampling, a protest should be issued and sample labels should be signed “For receipt only”. One bunker sample should always be retained on board. Useful documentation in a bunker quality dispute may be ship’s logbooks, oil record book, maintenance records, bunker tank contents records, consumption records, bunker receipts, photographs of damaged parts, survey reports, correspondence etc.
Insurance cover:-
For ship-owners, the standard Hull & Machinery (H&M) insurance will cover damage caused to the ship engines by bad bunkers. The damage to hull (DTH) element included in Charterers’ Liability Insurance will cover the charterer’s liability to owners for damage to the vessel as a consequence of the charterer supplying unsuitable bunkers to the ship. Charterers Liability Insurance also offers coverage for the charterer’s liability for extra bunker handling costs due to defective, contaminated or unfit bunkers.
How to avoid damage due to bad bunkers: Fuel Management.
There is a range of commercial, operational and contractual aspects that may be taken into consideration when trying to prevent bad bunker damage from occurring. The checklist below also serves as a summary of this circular.
1. Fuel purchasing
a. Selection of fuel specification. Ensure that the fuel is suitable for the vessel’s engine and in compliance with engine makers’ guidelines and environmental legislation.
b. Using fuel specifications. Make sure that the specification is communicated to the bunker supplier and properly set out in the charter party.
c. Be selective when choosing bunker suppliers.
If it is considered indeed it is a great mistake on the part of the ship's staff. So many other salient points are involved with the composition physical and chemical properties. If the fuel is off-specification the presence of various components and endangers the operation of the machinery.
The fuel was supplied on the basis of type (distillate or residual ) and viscosity (CST) but never mentioned the percentage of Sulphur (low or high), density (kg/meter-cube at measuring temperature in degree cel) and other soluble and insoluble components. It is a great lapse from the supplier too if by mistake the ship's staff mention the grade and type of fuel only. But it is the duty of the supplier to provide all specifications of the fuel oil. Considering this the supplier is also is a great fault by not furnishing the laboratory analysis report, hence the real scenario. As the fuel price is going up, all the companies trying to reduce the running cost, by using low-grade fuels. But if the actual composition is known protective measures can be taken before using the fuel. By using the fuel received at the last port, the exhaust valves of the main propulsion engine are damaged. The exhaust valve in the combustion engine experiences a very complex contact situation of frequent impact, involving micro sliding, high and varying temperature, complex exhaust gas chemistry and possible particulates. In addition, the tribological situation in the exhaust valve system may become even worse due to the presence of some corrosive and chemically active elements. The lack of protective failure is expected to result in increased wear of the contacts surfaces. The fuel oils that are used to run the main propulsion engine also adversely affect the engine parts due to naturally occurring elements present in the F.O. if not burnt efficiently. Corrosion is the primary concern on engine parts when it comes to burning off fuel oil. The corrosion may be categorised into two types 1. cold corrosion and 2. hot corrosion.
Hot corrosion- It occurs due to the presence of vanadium (V) and sodium (Na) in the fuel oil, which affects the exhaust valve and exhaust passage. vanadium is a naturally occurring element in marine fuel oil insoluble form, which means it can not be separated by filtering or through a centrifuge.
Vanadium and sodium combine at an elevated temperature, which takes a crucial role in hot corrosion. The availability of abundant oxygen in the combustion chamber, during the burning of fuel results in the oxidation of V to form VO (oxide) and VO2 (dioxide). During temperature drop, neither further combustion process VO further undergoes an oxidation process to form V2O5 (pentoxide). V2O5, has a low melting point and becomes sticky semi-liquid in nature and adhere to the surfaces they come into contact with. Sodium in the fuel reacts with the water vapour, during combustion to generate NaOH. This in turn combines with SO2, to form sodium sulphate (Na2SO4). Na2SO4 condenses at a temperature below 890°C and will adhere to the surface where already V2O5 is present these resultant deposits block the gas passage and corrode metal surface if the ratio of V: Na =3:1 the resulting complex melting point is at its lowest which is about 350-400° C and there is an increased like the hood of deposit formation. Fuels with high V and Na will increase the temperature for deposit formation in the exhaust passage. At high temperature(>650 deg cel)ash deposit can accelerate corrosion of metal and fouling of exhaust passage.
The second engineer, at first should be issued a letter of protest and compel the supplier to provide the laboratory analysis report. Should make them responsible and liable for any future consequences or damage to the engine parts, as they have failed to provide the particulars of the fuel oil as a statuary requirement by the marine law
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A. Apart from fuel specification, describe how you, as Second Engineer, should have assisted the owners’ case when receiving the suspect fuel.
A second engineer must emphasise the following points
1.1 MARPOL Annex VI contains requirements that apply to fuel oil used onboard ships. Regulation 14 sets limits on the sulphur content of fuel oil used on board ships, both within designated SOX emission control areas (regulation 14.4) and globally (regulation 14.1). Regulation 18.3 contains requirements that fuel oil delivered to and used onboard ships should not jeopardize the safety of ships or adversely affect the performance of machinery. Regulation 4.2.1.1 of SOLAS II-2 stipulates that except as otherwise permitted, no fuel oil with a flashpoint of less than 60°C shall be used.
1.2 Fuel oil purchasers are responsible for correctly specifying the fuel oil which is to be supplied. It is the responsibility of the supplier to deliver fuel oil that is compliant with the agreed specification and statutory limits.
1.3 These best practices are intended to assist fuel oil suppliers to ensure the quality of fuel oils delivered to ships that are compliant with the agreed specification and statutory limits.
1.4 When developing their procedures, fuel oil suppliers should also consider the guidance provided by existing industry practices and standards, for example, those published by the International Organization for Standardization (ISO).
1.5 This guidance does not apply to the supply of low flashpoint fuels such as LNG, LPG or methyl/ethyl alcohols, nor to pure bio-fuels.
B. Describe the ISO fuel standard that is to be used when ordering bunker fuel.
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| Fuel Oil Properties |
C. Explain how the correct fuel standard is selected.
a. Selection of fuel specification. Ensure that the fuel is suitable for the vessel’s engine and in compliance with engine makers’ guidelines and environmental legislation.b. Using fuel specifications. Make sure that the specification is communicated to the bunker supplier and properly set out in the charter party.
D. Suggest, with reasons, why particular mention should be made of certain elements that might not be included in the fuel standard.
following are the elements found in the fuel which are unavoidable, they do not contribute to the combustion process but are harmful to the engine and its components. additionally, to remove them extra arrangements are required to make such as purifier, clarifier etc. also they reduce the maintenance period for the engines and made the ship operation costly.
(a) Ash content
(b) vanadium and sodium
(c) calcium content
(d) sulfur content
(e) water content
Additional information regarding bunkering:-
Bunkers and bunkering could give rise to varying disputes between parties to a charter party or bunker supply contract. Disputes relating to bunkers could broadly be divided into three categories: quality disputes, disputes regarding quantity and problems as a result of the bunker supplier’s insolvency.
The quality of fuel may also be a source of concern in terms of compliance with MARPOL Annex VI and stricter sulphur-content regulation.
A dispute on the quality of bunkers may involve the ship-owners, charterer, bunker supplier and/or a possible intermediary, such as a bunker broker.
The quality of bunkers is an important issue for both the ship-owner and the charterer in order to ensure a smooth operation of the ship. In case the bunkers delivered on board are not within specification or otherwise unsuitable for the engine, this may result in severe damage to the vessel. This might in turn lead to delays and substantial consequential losses. Furthermore, arrangements may have to be made to de-bunker, which may be associated with large costs and could also mean deviations from the planned route.
Disputes between Owners and Charterers Under a time charter it is normally the charterer’s obligation to provide and pay for bunkers within a certain specification, which is normally set out in the charter party. However, under e.g. English law the obligation of the charterer goes beyond that: the stemmed bunkers also have to be reasonably fit for the particular vessel’s engines. This naturally implies that the charterer has been made aware of any particular characteristics or requirements of the engine. The ship-owners should thus make sure that the fuel specification is properly and clearly set out in the charter party, by referring to international bunker specification standards and stating special requirements of the engines. It should be noted that the most recent international fuel specifications allow for i.e. higher contents of cat fines than the recommendations of many engine makers. The legal situation under Nordic law is probably similar to the one in England. The requirement as to fitness for purpose may also be expressly included in the bunker clause in the charter party, which is usually the case. The shipowner however bears a heavy burden of proving that the stemmed bunkers were in fact off-spec and that there is a causal link between the poor quality of the bunkers and the machinery damage. Provided the ship-owner is able to lift the burden of proof, the liability imposed on the charterer may be substantial.
Disputes between the bunker purchaser and supplier: - The party responsible for providing for the vessel’s bunkers, either the ship-owners himself or a charterer, enters into a contract for the supply of bunkers on-board. It should be noted that the bunker purchaser’s contracting party is often not the actual fuel supplier. This may give rise to complex legal situations and attempts by the bunker seller to shove the responsibility onto the actual supplier. The bunker supplier usually uses its own standard terms and conditions of sale, which are favourable to the supplier and may be difficult for the buyer to renegotiate. The bunker purchaser should therefore be aware of short-time bars for the notification of a claim (sometimes as short as 7 days after delivery) and limitation of liability clauses contained in the supply contract. The prospects of negotiating amendments to the contract will depend on the buyer’s bargaining position. The bunker supplier has a duty to deliver bunkers within the specified grade of marine fuel and it is therefore important that the bunker order contains an appropriate description of the fuel to be supplied. The selection of a bunker supplier is usually a commercial decision of the shipowner but should be a balancing of quality and price aspects.
If a dispute as to bunker quality arises, the outcome of the dispute will usually be in the favour of the party being able to present the strongest evidence. It is, therefore, crucial to collect sufficient proof of the bunker contents and the incident. Bunker samples are usually drawn in connection with the bunkering and the ship-owners needs to ensure that the samples are representative of the entire delivery. By following the sampling procedures issued by the major fuel quality testing services of Veritas Petroleum Services (VPS) or Lloyd’s FOBAS, bunker purchasers can obtain representative samples which are accepted and signed by the supplier’s representative. It may well be that these are the only reliable samples, as the bunkers may then be mixed with bunkers previously supplied. It is important that the samples are properly sealed and labelled. In case the samples have been taken from the bunker barge and the ship-owners have not been invited to the sampling, a protest should be issued and sample labels should be signed “For receipt only”. One bunker sample should always be retained on board. Useful documentation in a bunker quality dispute may be ship’s logbooks, oil record book, maintenance records, bunker tank contents records, consumption records, bunker receipts, photographs of damaged parts, survey reports, correspondence etc.
Insurance cover:-
For ship-owners, the standard Hull & Machinery (H&M) insurance will cover damage caused to the ship engines by bad bunkers. The damage to hull (DTH) element included in Charterers’ Liability Insurance will cover the charterer’s liability to owners for damage to the vessel as a consequence of the charterer supplying unsuitable bunkers to the ship. Charterers Liability Insurance also offers coverage for the charterer’s liability for extra bunker handling costs due to defective, contaminated or unfit bunkers.
How to avoid damage due to bad bunkers: Fuel Management.
There is a range of commercial, operational and contractual aspects that may be taken into consideration when trying to prevent bad bunker damage from occurring. The checklist below also serves as a summary of this circular.
1. Fuel purchasing
a. Selection of fuel specification. Ensure that the fuel is suitable for the vessel’s engine and in compliance with engine makers’ guidelines and environmental legislation.
b. Using fuel specifications. Make sure that the specification is communicated to the bunker supplier and properly set out in the charter party.
c. Be selective when choosing bunker suppliers.
d. Be aware of the fuel supplier’s terms and conditions of sale.
2. Fuel delivery
a. Shipboard preparations. Make sure that receiving bunker tanks are as empty as possible before delivery or at least avoid mixing 50/50 with new and old fuel. Check that the sampling device is clean and fully operational.
b. Sampling and documentation. Agree on sampling methods with the supplier in advance. Follow procedures issued by major fuel quality testing services of VPS and Lloyd’s. Establish onboard procedures for bunkering, sampling and testing and for reporting and documenting irregularities.
c. Testing. Consider taking predelivery samples from the barge tanks and investing in an onboard test kit. It is recommended that a continuous drip sample is drawn at the vessel’s fuel manifold throughout the entire bunker delivery. Avoid using the new bunkers until the analysis results have been received.
3. Fuel Analysis
a. Chose an experienced and independent laboratory for analysis of the bunker samples.
b. Use the testing services to identify problem fuels and collect evidence.
4. Off-spec or unsuitable bunkers on board
a. Have a contingency plan for the most serious and likely scenarios.
b. Are the stemmed bunkers still useable? Many fuels which deviate slightly from the specifications may be consumed onboard, provided that the crew is aware of the problem and takes the necessary measures. In case the bunkers may cause serious damage to the machinery, de-bunkering should be arranged.
c. In case the defective bunkers may cause or have already caused damage to the vessel, contact your H&M (ship-owners) and P&I insurer (time charterers).
d. Involve technical experts and possibly also legal experts as early as possible.
e. Put the bunker supplier and time charterer on notice for a possible claim for the losses and costs incurred.
2. Fuel delivery
a. Shipboard preparations. Make sure that receiving bunker tanks are as empty as possible before delivery or at least avoid mixing 50/50 with new and old fuel. Check that the sampling device is clean and fully operational.
b. Sampling and documentation. Agree on sampling methods with the supplier in advance. Follow procedures issued by major fuel quality testing services of VPS and Lloyd’s. Establish onboard procedures for bunkering, sampling and testing and for reporting and documenting irregularities.
c. Testing. Consider taking predelivery samples from the barge tanks and investing in an onboard test kit. It is recommended that a continuous drip sample is drawn at the vessel’s fuel manifold throughout the entire bunker delivery. Avoid using the new bunkers until the analysis results have been received.
3. Fuel Analysis
a. Chose an experienced and independent laboratory for analysis of the bunker samples.
b. Use the testing services to identify problem fuels and collect evidence.
4. Off-spec or unsuitable bunkers on board
a. Have a contingency plan for the most serious and likely scenarios.
b. Are the stemmed bunkers still useable? Many fuels which deviate slightly from the specifications may be consumed onboard, provided that the crew is aware of the problem and takes the necessary measures. In case the bunkers may cause serious damage to the machinery, de-bunkering should be arranged.
c. In case the defective bunkers may cause or have already caused damage to the vessel, contact your H&M (ship-owners) and P&I insurer (time charterers).
d. Involve technical experts and possibly also legal experts as early as possible.
e. Put the bunker supplier and time charterer on notice for a possible claim for the losses and costs incurred.
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Awesome, never seen an explanation with a clear diagram which depicts even the minor features.
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