A must before starting any maintenance job.

v      As a thumb rule permission must be granted from relevant authorities as appropriate. A risk assessment must be carried out and a permit to work obtained. Additional relevant permits must be obtained if required (Enclosed space entry, Hot work permit, working aloft, etc). The work process must be conducted as per the “CODE OF SAFE WORKING PRACTICE” and the maker’s instruction.

v      During toolbox meetings, team members must be briefed regarding their job responsibilities. Proper tools and PPE must be used. Spares availability and lifting gears must be checked in advance. Only a qualified person must handle lifting tools. Remote control of the turning gear & overhead lifting gear must be handled by the person who is directly performing the job or a person who is closely monitoring the in charge.

 

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Tools, Parts and Materials (For Engine Cadets)

Reference: NYK CADET TRAINING NOTES

Bedplate of a Large Two Stroke Marine Engine

Bedplate:

A bedplate is the lowermost portion of a marine engine (2 and 4 stroke), which supports the engine structure and is also one of the most loaded constructional parts of the engine. For large engines, the bedplate is fabricated in parts with flat bottom type construction having high surface finish.

Construction of Bedplate:

The bedplate acts as the main strength member, maintains correct alignment and supports the weight of the components. it must be capable of withstanding the fluctuating forces created during operation and transmit them to the ships structure. In addition it may also collect lubricating oil.

In slow speed engine design, it consists of a deep longitudinal box section with stiffening in the form of members and webs.
Transverse members are fitted between each throw of the crankshaft. These support the main bearing saddles and Tie -rod connection. They are attached to the structure by substantial butt welds.To reduce the engine height the sump of the bedplate may be sunken allowing it to fitted into a recess in the ships structure.
Plate and weld preparation is required with welds of the double butt type if possible. Regular internal inspection of the parts especially the transverse girder is required for fatigue cracking. Tie bolts should be checked for tightness.

The advent of the small bore slow speed has seen the use of single side bedplates. A box section is then created by using a box section crankcase structure rather than the more traditional A-frame.This has the advantages of reducing width as well as weight and increasing the amount of fabrication so reducing assembly times.

Due to the weight penalty, the use of cast iron is generally limited to smaller units where fabrication becomes impractical. However, cast iron has internal resilience allowing it to dampen down vibrations, this has led to its usage on some medium speed installations, especially passenger carriers, where noise and vibration suppression is important.

The most highly loaded pat of a bedplate is the transverse girder. Classification societies require that residual stress is removed after construction.
The transverse girder acts as a simple beam with the forces of combustion acting on the piston passing down through the bearing. The forces acting on the head are passed through the Tie rods.

It can be seen that to reduce the bending moment the tie rods have to be brought closer to the crankshaft. The limit to this is the securing arrangement required for the main bearing keep. One method is to use two instead of one bolts which can be made of smaller diameter. Sulzer use an alternative and very successful method in the form of jacking bolts. These jack against the bottom of the A-frame.

The important functions of bedplate are:

1. To support the static load of stationary engine frame and blocks
2. To support the dynamic load of the running gear
3. To support the crankshaft and hold it in perfect alignment
4. To distribute the static and dynamic load generated by running engine onto the ship structure
5. To collect the crankcase lube oil and transfer it to the sump tank from where the lube oil pump can take suction
6. To fasten the engine to the tank top transmitting propeller thrust to the hull structure
7. To contribute to the hull strength of the ship at engine room bottom structure

Checks to be Carried on the Bedplate:

It is important to keep a regular check on the bedplate as it’s the foundation of the marine engine. The inspection of bedplate is also included in the planned management system of engine.

Following checks to be carried on the bedplate during inspection:

Cracks: Cracks is the most common problem that occurs on the bedplate structure. Following areas to be carefully checked for cracks:
Welding portion which joins the transverse girders to the longitudinal girders
Under the bearing pockets where cracks can emerge to be radial or follow the line of the pocket which holds the bearing
Radially at tie bolt and frame bolt holes
Around lightening holes provided in the bedplates and girders
At the base of main bearing keeps



Faulty welding: It is to be checked on newly delivered engine or if any welding repairs are carried out in the recent past


Faulty casting – It is to be checked on newly delivered engine with casting construction


Corrosion: As the bedplate is the bottom structure fitted in the bilge section of the engine room, it comes in contact with various fluids such as oil, water etc. and therefore is prone to corrosion. A close check should be made for identifying corrosion.


Loose Frames: The bedplate is held together with A frame and entablature of the engine by means of tie rod. Check the tie rod is tightened and there is no loose portion between the frame and bedplate.
Faulty Holding Down Bolts: The holding down bolts keeps the bedplate in position with the bottom structure of the ship. Check for loose holding down bolts and tighten as per the manual if found loose. Also, check for shearing and fretting on the holding down bolts.


Oil leakages: The bedplate is also responsible to collect the lube oil and transfer it to engine sump. Check for any oil leakage from the bedplate or the joint between the bedplate and the frame.


Ship’s engineers are responsible to ensure that marine engine bedplate is inspected at regular intervals of time and all faults are identified and repaired at the earliest. Failing to do so will result in heavy vibrations, misalignment of crankshaft, and reduction in engine efficiency and failure of engine components.

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Reference:

www.marineinsight.com

Marine Engineers' World (Facebook)

www.marineengineering.org.uk

Bangladesh Marine Academy

Details About ""BEDPLATE""

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Simply:  a bed plate or frame, usually of steel or cast iron, upon which an engine or other machine rests and to which it is attached.

Briefly: The bed plate acts as the main strength member, maintains correct alignment and supports the weight of the components. It must be capable of withstanding the fluctuating forces created during operation and transmit them to the ships structure.

The bed plate acts as the main strength member, maintains correct alignment and supports the weight of the components. It must be capable of withstanding the fluctuating forces created during operation and transmit them to the ships structure. It must be rigid enough to support the weight of the rest of the engine, and maintain the crankshaft, which sits in the bearing housings in the transverse girders, in alignment. At the same time it must be flexible enough to hog and sag with the foundation plate to which it is attached and which forms part of the ships structure. (If the bed plate was too rigid, then as the hull flexed, the holding down bolts, which secure the engine into the ship would be likely to break, and there would be a danger of the bed plate cracking.)

Construction: Basically the bed plate consists of two longitudinal girders which run the length of the engine. Connecting these longitudinal girders are the transverse girders which are positioned  between each crankshaft throw, and either side of the thrust collar. Built into the transverse girders are the main bearing pockets for the crankshaft to run in.

It Consists of the following;-

Longitudinal Girder (Fabricated) – the longitudinal strength is obtained by making each side of the bed plate in a form of a girder

Transverse (Cross) Girder – in which the main bearing are housed gives the bed plates its transverse strength

Longitudinal girder

Longitudinal girder apart from giving longitudinal strength, maintains alignment by giving sufficient rigidity (inflexible) to withstand the hogging and sagging of the ship’s hull.(single and double)

Ø  It provides a stiff support for the attachment of transverse girders (double)

Ø  Longitudinal girders may be of single or double plate construction

Ø  The double plate form is more stiff but would not be simple as single plate construction

Ø  The access to the holding down bolts will more difficult.

Ø  The use of single plate form is more popular with modern engines employed box bedplates and similar construction columns

Transverse Or Cross Girder

Consists of deep plate between the longitudinal girders, connected to the same on both sides.

Transverse girder carries main bearing pocket.

Ø  Deep plate is necessary for sufficient stiffness and to withstand the firing load without bending

Ø  Inadequate stiffness will distort (bend) the bearing pocket which will ‘nip’ the main bearing. This would ultimately grip the crankshaft journal and cause white metal to ‘wipe’.

Ø  These girders also may be of single or double plate form

Ø  The double plate arrangement gives high strength and stiffness.

Ø  Hole have to be cut in the plate to allow access for welding and inspection. These hole can seriously weaken a double plate arrangement in a small engine

Ø  A tube may be welded through the girder hole to restore strength and stiffness

Ø  The attachment of transverse girders to the longitudinal girders may differ (depending upon the material used).In most cases, it is welded

Ø  Some cases it may be bolted if the girder is cast, this reduces repair difficulties, allows stress relieving of the transverse girder only (classification society requirement). This also reduces risk of distortions

Modern Bed Plate: The modern bed plate is constructed from fabricated longitudinal girders with cast steel transverse sections containing the bearing pockets and tie bolt holes welded into place. After manufacture, the bed plate is stress relieved, the bearing pockets are line bored and landing surfaces machined. 

Fundamental requirement

Bedplate should provide an oil tight chamber, housing for the thrust bearing. Apart from that

Bedplate should fulfill the following:-

1          Strength

Ø  Necessary since considerable forces can be exerted.

Ø  In other word, withstand forces without failure.

Ø  These may be due to out of balance effects, vibrations, gas force transmission and gravitational forces.

2          Rigidity

Ø  Required to give correct alignment to running gear.

Ø  However, a certain degree of flexibility will prevent high stress that could be caused by slight misalignment (crack)

3          Lightness

Ø  Important, it may enable the power weight ratio to be increased.

Ø  In other word, to increase power weight ratio or power/weight (power more bigger than the weight)

Ø  Less material would be used bringing about saving cost

4          Toughness

Ø  In a material is a measure of its resilience and strength.

Ø  This property is required to enable the material to withstand the fatigue (weak) conditions (longer).

5          Simple design

Ø  In manufacture and installation are simplified to safe in costs.

Ø  Cast and welded joint

6          Access

Ø  Ease of access to the engine transmission system for inspection and maintenance on running gears purposes.

Ø  Inspection for crack at bearing pocket and welded joint also for tie bolts and holding down bolts etc.

7          Dimension

Ø  Ideally these should be as small as possible to keep engine containment to a minimum in order to give more engine room space.

Ø  However must can be fix with frame.

Ø  Ideally these should be as small as possible to keep engine containment to a minimum in order to give more engine room space.

Ø  However can be fixing with frame.

8          Seal

Ø  Must seal off effectively the oil and vapors by providing oil tight chamber and housing for thrust block

Ø  Any vapors or oil flowing out from it mean crack have been occur.

Faults in bed plates

The bedplate should be inspected regularly for evidence of cracking. This can occur in the welds joining the transverse girders to the longitudinal, and under the bearing pockets, where the cracks can be radial or follow the line of the pocket. As well as faulty manufacturing techniques, causes can be uneven loading/ overloading of engine units, loose tie bolts and loose holding down bolts.

Type of Faults

Ø  Cracks

Ø  Oil leaks

Ø  Loose chokes

Ø  Loose frames

Crack areas

 

Ø  Fabricated transverse girders often show cracks in welds around the bearing pockets.

Ø  Radically around tie bolt and frame bolt holes.

Ø  At the junction welds between fabricated cross girder and side girder.

Ø  Around lighting holes.

Ø  At the base of main bearing keeps.

Reason for failures or cracks

Ø  Excessive vibration

Ø  Slack tie bolts

Ø  Overloading due to excessive bearing wear

Ø  Poor welding or stress relieving

Ø  Stress riser (concentration) on weld

Repairs

Ø  Mild steel or cast steel materials – crack should be chipped out and welded. Care should be taken not to distort the welded part – repair to be done by ductile electrodes which will give deposit close to parent metal

Ø  Cast iron – Can be arrested by drilling (if small) and metallocked (if serious) and support by doubler-plate bolted on it

Bedplates inspection

Ø  Cracks

Ø  Corrosion – moisture or acidic compounds

Ø  Cleanliness – sludge and carbon

Ø  Loosen connections

Ø  Oil leaks

Ø  Faulty welding

Ø  Faulty casting

Ø  Cracks

Ø  Corrosion – moisture or acidic compounds

Ø  Cleanliness – sludge and carbon

Ø  Loosen connections

Ø  Oil leaks

Ø  Faulty welding

Ø  Faulty casting