Ship repair

 

Damage This represents reduction of the health of the ship component through direct impact of weapons, collisions or exposure to damaging effects of heat and radiation. Whether that is an installed module, or integrated component such as the ships hull, cockpit viewports or ship armor. Damage is corrected through Repair.

Wear. This represents the degradation of ship components over time through use. Whether that is an installed module, or integrated component such as the ships hull, cockpit viewports or ship armor. Wear is corrected through maintenance.

Aging: This represents the gradual degradation of the overall ships condition. This is mostly cosmetic and affects the ship as whole not individual components. Things like the appearance of scratches on the cockpit viewports, the condition of the paint, interior surfaces and upholstery. Aging is corrected through restoration.

Causes

Causes of Wear and Damage.  The loss of original qualities is associated with the appearance of various forms of damage caused by:

 

a.         Frictional wear,

b.         Corrosion,

c.         Erosion,

d.         Metal fatigue,

e.         Heating of parts to high temperatures

f.          Change in metal structure,

g.         Poor construction and inadequate repairs,

h.         Arduous working conditions

j.          Break downs, etc.

 

Effects.         

Damage. As a measure of the health of a component, this would reduce the components effectiveness as damage is accumulated. It should be an escalating scale from perfect working order to no longer functioning. Having 100% damage does not destroy the component but merely renders it inoperable until repaired and its damage reduced to at least 99% damage. This effect is applied to and tracked individually by each component.

Wear.   As a measure of gradual degradation, this would represent the likeliness for a component to suffer a random failure or suffer critical damage. A random failure represents a temporary and premature failure of the component. A random failure can be resolved through the repair of just 1% damage. This can be accomplished by an auto repair unit or through the shutdown and repair feature. Critical damage represents a damaging event to the component that applies 25% damage to the component but does not cause component failure unless the total damage reaches 100% by this event. A component with 100% wear is still fully functional but more likely to fail or suffer damage. Think of this as reliability. At 100% wear it would represent a 25% likelihood of either random failure or critical damage when taking additional damage or module activation. This effect is applied to.

Aging.  As a overall measure of ship condition this has little effect on the capabilities of the ship or its components but serves primarily as a visual measure of the life the ship has lived. As ship with a low level of aging will look like it just rolled off the showroom floor while a ship with a high level of aging will look like its been through a rough life. It could also work in the same way as wear but to a much smaller degree and would affect all components equally. At 100% aging it would represent an additional 5% likelihood of a random failure or critical damage. This effect is applied to the ship as a whole.Cylindrical parts can become elliptical conical, or barrel shaped. As a result of the wearing process, the oil clearances are also changed the alignment of parts and machinery is disturbed and scuffing of the rubbing surfaces may occur.

Method to Detecting the Damage. To determine the condition of parts mechanisms, or engine elements, and to ascertain the amount of maintenance work, it is necessary to test them thoroughly when making defect survey. These tests arc made using methods of;

 

a.   Physical Procedures.   Physical procedures include X-ray, gamma-ray, ultrasonic, magnetic, luminescent, and colour tests. These methods of defect analysis permit the detection of defects in castings or forgings (slag inclusions, cavities, gas pores, cracks), in welded joints and ready-made articles.

 

b. Technological Inspection

 

Uses of Physical Procedures.    X-ray, gamma-ray, and ultrasonic inspection is used mainly to detect internal defects in metals magnetic inspection to defect subsurface and surface defects, and Luminescent and colour inspection to detect surface defects.

 

Advantages of Physical Procedures.   The advantages or physical, procedures include their relative simplicity high sensitivity accuracy and the possibility in many cases of detection defects without dismantling the individual units and connecting.

 

Technological Inspection.           Technological inspection procedures consist in visual inspection (with various degrees of magnification), dimensional, measurements, chalk —kerosene and magnetic —kerosene methods, electrolytic etching tightness etc.

Method of Finding the Thickness of Ships Hull Plate.   Thickness reduction of structural elements in ships occurs mainly as a result of corrosion. The measurement of the ship plates or other structural parts can be made from one side by means of an ultrasonic thickness gauge. Also widely applied is a method of determining the thickness of plates by drilling check holes and using linear dial gauges etc. The salient aspects of measurement of the ship plates or other structural parts are discussed below:

 

a.            Liner dial gauge.     The linear dial gauge has a socket 1 and a retaining sleeve with a claw 2 the indicator spindle is pointer, and the socket is fitted to the upper end of the indicator in such a way that the point of the needle coincides with the upper plane of the socket .At the other end of the indicator there is the retaining sleeve with the claw pointer set so that the points of the needle claw are in contact. The indicator should read zero at this setting. The indicator permits measurements of thickness up to 10 min: with a greater thickness, the claw and needle points are set for a gap of 10min. and this figure is added to the subsequent readings of the indicator.

 b.            Two rulers system.            When measuring the corrosion damage in the shell plating, double bottom bulkheads , and other parts , plates with the most extensive damage are chosen .When pits are present on the surface of the plates the amount of damage is determined in the following way. On each plate a square circumscribing the most affected parts is chosen, the area of the square is measured and an estimate is made of the areas of the pit and cavities. The means thickness of the wasted plates round and inside the cavities is also found.

 c.         To find the area affected by the cavities, a grid is chalked, or a frame with a wire grid is placed on the surface under consideration. The area of each cavity is estimated against the area of the superimposed grid squares.

d.         The ratio of the number of affected squares to the total number of squares in the frame, multiplied by 100 gives the percentage area of damage in the given region. Where the pitting type of corrosion is not present, the trickiness of a given zone is taken as the mean of several readings. Then the mean thickness of other zones within the tested portion of the plating is found.

e.         The depth of a cavity may be found using an indicator which is placed so that the probing socket 1 rests against the surface or making a cast replica of the cavity in plasticine, wax, or stearin and measuring its height. 

Method of Detecting Surface Crack.     Crake are a form of damage which is most widely distributed over parts of hull, boilers and machine parts. Below, a description is given of the most common methods of detecting cracks.

 

a.            Visual Method.        The visual method consists in observing with naked eye or through a magnifying glass the surface of plate, machine part, welded seam, etc. The method is simple but very tedious and not always reliable, since the smaller cracks are difficult to detect. Only visible cracks can be revealed by the naked eye .A strong illumination of the examined surface helps in detecting cracks. Smaller cracks can be revealed with the aid of a magnifying glass.

 

b.            Chalk—Kerosene Methods.        Chalk —kerosene methods are used for detecting cracks and also in tests for tightness, continuity of plate laps and butts quality of seams. etc. The detection of cracks on the surface and the determination of their extent are carried out as follows. The area under examination is thoroughly cleaned and copiously wetted with kerosene; then it is wiped dry and covered with a chalk solution with chalk. Next the tested zone is vibrated by hammer blows using a copper protecting plate, near test area. The presence and extent of a crack are revealed by a greasy trace caused by absorption of kerosene by the chalk .The vibration causes the egress of the kerosene from the crack. When testing welded seams both sides of the seam should be cleaned and dried. Then the seam is wetted with kerosene so that a thin film of kerosene is present on the surface during the test.

 

c.            Magnetic Testing Methods.         Magnetic testing methods have found. a wide application in detecting cracks in steel and cast iron parts, owing to their relative simplicity and effectiveness.

 

The principle of the method is to magnetize the part and apply iron powder to its surface. In the wet version, the powder is introduced to a receptacle containing dehydrated kerosene and the part immersed. The iron powder will concentrate along the boundaries of the cracks as a result of the formation of supplementary poles.

 

The wet magnetic method finds application in ,for example, examinations of turbine blades .A container with the mixture of dehydrated kerosene and iron powder is placed under the magnetized disks and blades; Rotating the rotor- the blades are immersed and thoroughly examined for concentration of iron powder denoting cracks .The dry method is less widely used than the wet method.

 

d.            Electrolytic Etching.   Electrolytic etching is used to reveal cracks fissures and slag inclusions. As a result of etching the cracks and fissures are marked with corrosion products, and slag inclusions are indicated as light streaks.

 

In etching the part is placed as an anode in an electrolytic bath. A mixture of 2% nitric acid and 2% sulphuric acid is used as electrolyte, and a plate of stainless steel as the cathode , The parts remain in the bath for 10 to 12 min , with a voltage of 10V and current density of 0.1 A per square centimeter of the tested surface . The examination is made after removed of the parts from the bath when they are still wet.

 

e.            Etching the Surface in Acid Solutions.  Etching the surface in acid solutions is analogous to the etching revealed clearly because their edges are attacked more strongly than the rest of the surface.

Importance of Watertight Integrity.        If flooding of one compartment as a result of damage to the hull or the failure of an internal pipe system carrying liquids,  specially if under pressure, is to be prevented from spreading to adjoining compartments progressively throw out the ship, it is essential that compartment boundaries be maintained in a completely watertight condition. This entails absolute integrity of decks and bulkheads, and complete water tightness of fittings in them which control necessary openings such as doors hatches, valves and glands. As an example of the problem , a hole only 129 sq mm in the hull 3 mtr  below the waterline will admit water at a rate greater then a submersible pump [ 40 tone / hour capacity] can remove it an equivalent area can easily be made up of the sum of a number of small holes, e.g bolt holes and cable glands left open after equipment or cables have been removed, leaking door and hatch joints, defective ventilation valves, etc.

 Checking of Watertight Integrity.    To ensure that compartments retain their water tightness it is necessary to carry out regular and thorough visual examinations to detect the more obvious sources of leakage backed up by routine tests to reveal any hidden or less readily visible leaks that may exist. It is especially important to check compartments in which structural or other work has taken place which could affect their watertight (or gastight) integrity; for example, when equipments have been removed during a refit. Any shortcomings revealed by visual examination or by tests must be rectified as soon as possible. The succeeding paragraphs describe briefly the tests which are to be carried out by ship's staff to check the water tightness of compartment boundaries and closures. Detailed information about these tests and lists of compartments to be tested are contained in BR 3000, hull maintenance schedules and hull ship equipment lists.

Bulkhead.     Bulkheads Vertical partitions in a ship arranged transversely or fore and aft are referred to as `bulkheads'. Those bulkheads which are of greatest importance are the main transverse and longitudinal bulkheads dividing the ship into a number of compartments. There are others, which are of little structural importance, but they act as screens further dividing compartments into small units of accommodation and stores.

 

Types of Bulkhead.          

 a.         According to position there are two types of bulkheads construct in ship building:

 (1)    Longitudinal Bulkhead.

2)    Transverse Bulkhead.

 

b.         According to function bulkheads are generally two groups:

 (1)    Water tight (WT) Bulkhead.

(2)    Non Water tight (WT) Bulkhead.

 

c.         According to use of shell plate, bulkheads are generally two groups:

 

(1)    Corrugated Bulkhead.

(2)     Plane Bulkhead.

 

Function of Bulkhead.      Bulkheads fulfils following function:

 

a.    They hold the ship to form and effort support local loads, Such as are more decks, gun mountings etc.

b.    Main bulkheads contribute largely to structural strength and protect important compartments against under water expolsion.

c.    Bulkheads are an important element of transverse strength, particularly against racking stresses.

d.    By dividing the ship into longitudinal subdivision, they also give protection against fire and foundering.

 

Fitting of Bulkhead.           It may be fitted in the ship longitudinally and transversally according to the ships length and design.

 

Transverse Bulkhead.      The fore most transverse bulkhead usually about 30 ft from the bow is large ship is called the collision bulkhead. it is continuous from the keel to the fore castle deck and well stiffened vertically.

Main transverse bulkhead are generally worked in horizontal strake with the vertical stiffening between main machinery compartment the bulkhead extended from the protective deck to the inner bottom without support from deck or flats.

  

Longitudinal Bulkhead.    The number and deposition of main longitudinal bulkheads depends on the class of ship capital ships have generally three such bulkheads a amidships the inner one bounding the main machinery compartments and the outer one constructed and the outer constructed to prov9ide protection against under water explosion.

 

Use of Bulkhead.    The watertight bulkhead of a ship has several functions to perform. They are:

 

a.            They provide the ship into watertight compartment.

b.            The watertight bulkhead also serves to separate different types of cargo and to provide tanks.

c.            In the event of fire the bulkhead reduce to a great extend the rate of spread.

d.            The transverse strength of the ship is increased by the bulkheads.

e.            This prevent under distortion of the shell side reduce racking considerably.

f.             Longitudinal deck girders and deck longitudinal are supported at the bulkheads which therefore act as pillar.

 

Corrugated Bulkhead.      Due to shape and design there is a another bulkhead named corrugated bulkhead this may come from as transverse and longitudinal as design generally it is fitted in the liquid tank to reduce the free surface effect.

 

Water Tight Subdivision.             Water tight subdivision achieved by:

 

a.         Main transverse bulkhead.

b.         Main longitudinal bulkhead.

c.         Watertight door and hatches.

d.         Watertight deck

e.         Double bottom.

f.          Some minor bulkhead.

 

Advantage of Watertight Subdivision.    Following are the advantage of water tight subdivision:

 

a.         It contributes the strength of the ship.

b.         It increases the resistance to damage of the ship.

c.         It localities or limits the hooding and fire.

d.         It contributes or increases the reserve buoyancy.

e.         It improves the habitability.

f.          It improves facility to presentation of stores water fuel etc.