LATEST SAFETY MMD ORAL QUESTIONS & ANSWERS PART-8

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(a) What are destructive tests and non-destructive tests?

(b) Describe two methods of destructive test and one method of non-destructive test.

(a) Destructive test

  • Test on test pieces Damaged after test.
  • Determine mechanical properties of test piece under test.

(1) Tensile test 

(2) Bend test

(3) Impact Test

(4) Hardness Test

(5) Fatigue Test

(6) Creep Test

Non-Destructive Test

  • Test on components. Not damaged after test
  • Determine flaws or imperfection during manufacture (or) service.

(1) Liquid penetrating

(2) Ultrasonic method

(3) Magnetic crack detection

(4) Electrical test method

(5) Radiographic inspection

Destructive test

(1) Tensile Test

  • Tensile test is used to determine the behaviour of a material up to its breaking point.
  • A special shape specimen of standard size is gripped in the jaws of a testing machine. A load is gradually applied to draw the ends of the specimen apart such that it is subject to tensile stress up to yield point.
  • The highest value of stress is known as the ultimate tensile stress (UTS) of the material.

(2) Bend Test

Specimen is bent through an angle of 1800 with internal radius of 1.5 times the thickness of the specimen without cracking at edges.

(3) Impact Test

  • Testing machine basically consists of a pendulum which is raised and allowed to fall, striking and rupturing the specimen.
  • In swinging through its arc of travel past specimen, pendulum assume a lower position at end of its travel due to loss of energy when it strikes the specimen.
  • Energy given up to the specimen is its impact strength.

(4) Hardness Test

  • Hardness test consist hardened steel ball impressing into metal at given pressure for predetermine time.
  • Load is 3000 kg for steel and 500 kg for soft metals such as brasses and bronzes.
  • Diameter impression indicates the hardness number.

(5) Fatigue Test

  • Fatigue’ is defined as the failure of a material due to repeatedly applied stress.
  • The specimen is rotated under load in a testing machine. So it is subject to tension and compression stresses alternately.
  • The number of cycles imposed before is recorded.

(6) Creep Test

  • Creep test use to find safe working stress for material working at high temperature
  • It is permanent deformation resulting from loading over long period of time
  • Test piece mount vertically and constant tensile load under constant temperature.
  • Temperature range between 600’C to 1000’C and test period is 1000,10000,100000 hours

Non-Destructive Test

(1) Liquid penetrate test

Industrial method, indicate presence crack, lamination lap and surface porosity.

Fluorescent dye method and Aerosol dye method.

Fluorescent dye method

  • First, the surface is cleaned using a volatile cleaner and degreaser.
  • Then a fluorescent dye is applied and a certain time allowed for it to enter any flaws under capillary action.
  • Then the surface is wiped clean using the cleaning spray.
  • An ultra violet light is shone on the surface, any flaws showing up as the dye fluorescent.

Aerosol dye method

  • The more commonly used dye penetrant method is similar in application.
  • The surface is cleaned and the low viscosity penetrant is sprayed on.
  • After a set time, the surface is cleaned again.
  • Then a developer is used which coats the surface in a fine white chalky dust.
  • The dye seeps out and stains the developer typically a red colour.

(2) Ultrasonic Test

  • Probe of test equipment transmits high frequency sound waves about 0.5 MHz to 20 MHz which reflected by any flaws in object
  • Reflected sound waves displayed on monitor screen of cathode ray oscilloscope.
  • Suitable for detection, identification and size assessment of a wide variety of both surface and sub-surface defects in materials.
  • Measured thickness of material or to detect internal or surface defects in welds, casting or forging either during manufacture or when in service.

(3) Radiographic Test

  • Image produced on film.
  • X rays and gamma rays are used for inspection of welds, castings, forging and pressure vessels etc.
  • Exposure time for x-rays and gamma rays vary with type of material, thickness and the intensity of rays.
  • Faults in the metal effect the intensity of rays which passes through the material
  • Film exposed by the rays gives the shadow photograph
  • Used on both metallic and nonmetallic material, both ferrous and non-ferrous metal.

(a) Sketch an oxygen meter suitable for checking the atmosphere within the enclosed space.

(b) Explain the operation of the above meter.

(c) Explain why indication of satisfactorily oxygen content does not necessarily mean that it is safe to enter a space.

(a) Paramagnetic type Oxygen meter

(b) Paramagnetic Oxygen Meter

  • Dumb-bell type paramagnetic oxygen analyzer based on magnetic susceptibility(sensing) of Oxygen gas.
  • In the cell, two glass spheres filled with nitrogen gas are suspended with strong metal.
  • At first, spheres kept in balance in an inhomogeneous magnetic field.
  • When oxygen molecules flow there, molecules pulled towards stronger magnetic field zone.
  • Spheres moved away from the zone.
  • The resulting deviation of spheres detected with light source, reflecting mirror and light receiving element.
  • A current flowed through the feedback loop; controls spheres to return to initial balanced state.
  • This current flow is proportional to oxygen concentration and displayed on meter as Oxygen gas concentration.
  • This detector is suited to use in flammable gas as it has no heating part such as heater.

(c) Oxygen meter reading is only Oxygen % by volume at atmospheric pressure.

  • It means Oxygen partial pressure is 21% of 760 mm Hg (millimeters of mercury) = 159 mmHg.
  • Due to water vapor and CO2 at alveolar space in lung, Oxygen partial pressure becomes 110mm Hg.
  • This oxygen partial pressure allows Oxygen flow from lung into blood, CO2 flows from blood into the lung and it said safe.
  • If any gases leak into space, resulted Oxygen depletion will reduce Oxygen partial pressure at alveolar space in the lung. It said hazardous condition.
  • Oxygen meter reading of 21 % by volume at atmospheric pressure lower than 760 mmHg, oxygen meter reading is 19.5% by volume, it said not safe.

(a) Discuss problem that may result from the used, storage and handling of modern residual fuel of poor quality.

(b) State how a valid fuel sample is obtained while bunkering.

(c) Describe briefly onboard tests available for assessment of fuel quality.

(a) Problem of used of residual fuel

1. Up setting of purifier operation.

2. At fuel pump components, high wear rate, due to ashes and cat fine

3. At nozzle sprayer, spray holes blockage, leakage and corrosion of injector.

4. At piston ring and cylinder liner, high wear rate due to high Sulphur content

5. Excessive ring zone deposits cause incompletely burn combustion products

6. Shorter exhaust valve life due to low temperature corrosion and hot corrosion.

7. On turbocharger nozzle ring and turbine blades, solid deposit and corrosion

8. Up take and economizer corrosion and fouling.

9. Mineral acid from combustion product causes serious corrosion hazard

(b) How a valid sample is obtained while bunkering

When bunkering sample taken as follow;

(1) Take fuel oil samples by continuous-drip method throughout bunkering.

(2) During bunkering, spot check at random time from bunker line and spot check at random tank form bunker barge

(3) Each one sample for laboratory analysis (DNPS or others), for vessel, for MARPOL, for supplier. For charter if requested.

(4) Keep all samples for a period of not less than 12 months from date of bunkering or until time all fuel consumed whenever is later.

(c) Onboard test available for assessment of fuel quality

  • Full fuel analysis done only by shore laboratory.
  • Most onboard test-kits give reliable result for specific gravity, viscosity, pour point, water content and compatibility.

1. Density or specific gravity: found for fuel at a particular temperature with a test kit hydrometer. It is required for bunker calculation and purifier gravity disc selection.

2. Viscosity: used simple method 3 tube rolling ball viscometer require for improve separation & good pumping

3. Flash point: found with a Penksy Martin closed cup apparatus.

4. Pour point: found by cooling preheated-oil in a test tube and at every 3˚C drop in temperature, tilt tube to see still free flowing or not.

5. Water content: sample oil mixed with a reagent in closed container and any water in the oil reacts with the chemical reagent to produce a vapor. Pressurized vapor calibrated to show water percentage.

6. Compatibility: A sample mixes with a residual fuel and another fuel in equal amounts and deposits a drop on Photochromatic paper. After an hour, the pattern left is compared with spots on a reference sheet

(a) Describe how lube oil contamination may arise in an engine.

(b) Describe the test for contaminated lube oil on board.

(a) Lube oil contamination

(1) Water dilution

  • Leakage from C.W system (cylinder or piston), defective sea water, cooler tube, steam heating.
  • Condensation from vapor, in crankcase.

(2) Fuel oil dilution

  • Caused by dribbling fuel valve and leaking fuel pump due to excess wear of its components.

(3) Oxidation Products

  • Mineral oils react with oxygen in the air.
  • More contaminants formed, higher temperature and greater contact with air.

(4) Fuel combustion products

  • Incomplete burnt fuel, form sludge and deposits, seriously effect engine performance.

(5) Solid Impurities

  • Solid impurities from wear and tear. Rust and scales from Storage tank and pipes etc. Dust from surrounding atmosphere.

(6) Biological Contamination

  • Cause due to water contamination. Forming of organic acid Additive depletion Corrosion of shaft & bearing.

(b) Testing Lube oil on board (ACDV Kit)

Acidity determination

  • Tested by extracting acid from sample by shaking with a known amount of distilled water.
  • The extract acidic placed on a watch glass with an indicator solution known strength.
  • The mixture is drawn up into a glass tube and compared with a series of color standards
  • Each representing pH value, sample determined quite accurately.

Water and other contaminants (crackle test)

  • Amount of sample oil into a test tube and holding it over a small spirit lamp, shaking tube while so doing.
  • No crackling -oil is dry, slight crackling indicate – trace of water
  • Insoluble content (blotter test)
  • A single drop of sample oil, is released from a given height on to a sheet of special filter paper.
  • Result compares with similar oil. Test oil below the upper limit

Viscosity determination

  • Simplest method is 3-tube rolling ball viscometer.
  • Assume oil from engine is SAE 30 grade, one tube filled with minimum safe viscosity (about SAE 20) and other tube with optimum viscosity (about SAE 40), and last tube to be filled with test sample.
  • All tubes are placed in hot water bucket until the oils are at the same temperature.
  • The three tubes, mounted on a tilted board, are then inverted. Each tube, an internal hollow ball rises to the surface.
  • Test sample is between lower and upper limit oils, oil is fit for further use.

(a) Sketch a single flash type fresh water generator

(b) Describe the above

(c) State methods of post distillation treatment for drinking purpose.

(a)

(b) Single flash type fresh water generator

  • Consists of three main parts – heat exchanger, separator and condenser.
  • For heating of sea water to evaporate, the waste heat from jacket cooling fresh water is used.
  • For condensation of the vapour, sea water from main sea water pump passes through condenser.
  • Equipment required to be vacuumed about 93%.
  • Ejector pump supplies sea water to vacuum ejector, brine ejector and also feed sea water line
  • Feed sea water passed inside tubes of heat exchanger and evaporated by means of jacket cooling water temperature about 70 °C.
  • The sea water droplets in the vapour are deflected by separator.
  • This vapour is passed to the condenser tubes and is condensed by sea water cooling.
  • The residual brine goes to brine ejector.
  • Salinity of produce fresh water is automatically checked by salinometer system.
  • When salinity is higher than set value, solenoid valve operates and produced water drained into bilge.

(c) Methods of Post-distillation treatment for drinking purpose

  • If an evaporator runs remote from coastal water and at a minimum distillation temperature of 72°C, produced water is free from micro-organisms.
  • If this condition cannot be met, sterilization must be done.
  • Methods of Sterilization are (1) Chlorination, (2) Ultra Violet light, (3) Ionizing silver in the water.
  • Most common method is Ultra Violet light unit, fitted at discharge side of portable water storage tank or hydrophone.
  • The light kills micro-organism without causing physical and chemical change in the water.
  • Chlorination is to inject chlorine as a solution of Sodium hypochlorite (NaOCL).
  • Ironing silver is also an effective means of sterilizing water even in concentrations as low as 0.005 ppm.
  • To produce clean water, sand bed filter used.

With respect to heat treatment of the steel, write short on the following subjects-

(a) Tempering

(b) Normalizing

(c) Induction hardening

(d) Nitriding

(e) Case Hardening

(f) Flame Hardening

(a) Tempering

  • Employ to relieve quenching stress and to toughen steel
  • Steel heat to 200’C-400’C below critical temperature, follow by cooling
  • Higher temperature slowly cooled state.

(b) Normalizing

  • Normalizing cheaper and quicker than annealing, cooling rate cannot control.
  • Steel heat slightly above critical, allow to cool freely in still air at room temperature.
  • Stronger and harder than annealed steel. Less suitable for cold working, more suitable for putting into service.

(c) Induction hardening

  • This process heating carried out by electro-magnetic induction
  • The part to be hardened surrounded by induction coil, alternating current of high frequency passed through
  • (Eddy currents produce raise temperature of component to above upper critical temperature in 3-5 sec)
  • Short time of heating reduce change of gain growth

(d) Nitriding

  • Special alloy steels immersed in ammonia gas at 500’C for period up to 88 hours
  • Iron nitride extremely hard and Treatment carried out below lower critical temperature, no quenching necessary
  • Structure of steel unaffected, no distortion, cracking or scaling
  • Parts finish ground before nitriding.

(e) Case hardening

  • Both plain carbon and alloy steels use for case hardening
  • Carbon content not exceed 0.3 % if reasonable core toughness maintained
  • Manganese added to case hardening steels to aid carburization and increase depth of hardening cause graphitization.
  • Alloy case hardening steel contain nickel and chromium. Chromium added to increase hardness

(f) Flame hardening

  • Steel surface heated by moving oxy-acetylene flame to above upper critical temperature follow by quenching by water spray
  • Small addition of nickel and chromium to improve strength and case hardness
  • Components usually normalized before hardening to ensure toughness of core

(a) In these days how many types of Hull protection systems are using on ships.

(b) Explain detailed principle of Impressed Current Cathodic Protection System with sketch

(c) What is MGPS system and explain briefly.

(a) Types of Hull protection systems used on ships are:

(1) Sacrificial Anode System: anodes fitted on ship hull to protect hull metal wastages.

(2) ICCP: Impressed Current Cathodic Prevention System

(3) Paint: cover layer of hull metal.

(b) Principle of ICCP system

  • ICCP system protects surface of ship hull. When equal potential on surface, corrosion effect is forced to stop
  • ICCP system basically consists of (1) DC current source, (2) anodes, (3) reference cell (4) converter and controller units (5) high quality inert protective coating on hull around the anodes.
  • In converter unit, AC current transformed and rectified to DC current before supplying it to anodes.
  • Anodes made of lead or platinized titanium, fitted in special recess boxes on ship’s hull.
  • Reference cells made of silver / silver chloride.
  • Protective coating of epoxy resin is applied, on hull around anodes for a radius of 1 meter or more, to provide a dielectric shield.
  • Controller unit detects voltage between hull and reference cell and amplifies micro range reference cell current.
  • Compares with preset value and automatically regulates anode current to required value.
  • Impressed current required varies with (1) underwater hull area, (2) ship speed, (3) salinity (4) hull paint condition
  • Low current cause inadequate protection and a high current damage paint work.
  • Propeller shaft and rudder bonding arrangements fitted with impressed current systems to ensure propeller and rudder protection.
  • When alongside a jetty, system switched-off, not to protect jetty.
  • For tanker, while loading or discharging, system switched off

(c) MGPS: Marine Growth Protection System

  • Marine growth grow in ship internal sea water piping systems. This causes;
    • Engine Overheat
    • Pipes and valves become partly choked or totally blocked.
  • MGPS system is based on electrolytic principle. Anode and Cathode metals submerged in sea chest or special electrolysis tank.
  • A small dc current allowed to flow through copper and aluminum anodes.
  • Copper produces copper ion which prevents marine growth
  • Aluminum produces aluminum hydroxide which prevents corrosion on internal surface of pipes.
  • This system is effective, reliable and safe in operation.

Q. What are the classes of fire?

Ans- There are 3 class of division for fire :-

1. “A” class division :-  division formed by the bulkheads & decks which comply with the following :

  • They should be constructed of steel or other equivalent material.
  • They should be suitable stiffened.
  • They should  be so constructed as to capable of preventing the passage of smoke & flame to the end of the 1 hour standard fire test.
  • They should be insulated with the approved non combustible materials so that the average temperature of unexposed side will not increase more than 140°c above the original temperature, nor will the temperature at any one point , including any joint, rise more than 180°c  above the original temperature within the time listed below:

 Class”A-60″                 60 minutes

 Class “A-30”                30 minutes

 Class “A-15”               15 minutes

Class “A-0”                   0 minutes

The administration may require a test of the prototype bulkhead or deck to assure that it meets the above requirement for integrity & temperature rise.

2.  “B” class division :- are those division formed by bulkheads, decks , ceiling or lining which comply with the following :

  • They should be so constructed as to be capable of stopping the passage of flame to the end of the first 1/2hour of the standard fire test.
  • They should have an insulation such that the average temperature of the unexposed side will not increase more than 140°c above the original temperature, nor will the temperature at any one point, including any joint, rise more than 225 °c above the original temperature within the temperature within the time listed below :

Class “B-15”.                  15 minutes

Class “B-0”                     0 minutes

They shall be constructed of approved non combustible materials & all materials entering into the construction & erection of the “b” class divisions shall be non combustible with the exception that combustible veneers may be allowed provided that they meet other requirements.

The administration may require a test of a prototype bulkhead or deck to assure that it meets the above requirement for integrity & temperature rise.

3. “C” class division :- are the divisions constructed of the approved non combustible materials. They need meet neither requirements relative to the passage of the smoke & flame or limitations relative to the temperature rise. Combustible veneers are allowed provided they meet the requirement.

Q. How Ism code defines NC (non conformity) ?

Ans– Ism code defines NC (non conformity) as

A non conformity means a situation where evidence indicates the non fulfillment of the specified requirement of the ISM code.

When an non conformity is found, agreement must be reached with the management of the department concerned that the perceived non conformity exists. Certificate can be issued provided suitable corrective action & appropriate time scale (not exceeding 3 months) is agreed. Closure of an non conformity does not need a revisit by the auditor. Written notification of completion of the corrective action accompanied where possible with objective evidence must be forwarded. An non conformity which is not corrected with the stipulated time frame may be upgraded to a major non conformity & result in cancellation of the certificate.

Q. Capacity Plan

Ans– A plan of the spaces available for the cargo, fuel, freshwater, water ballast, etc, & containing cubic or weight capacity lists for such spaces & a scale showing deadweight capacities at varying draughts & displacements.

Q.  DWT Scale

Ans– This scale also shows the moment to change trim 1 cm & the TPC for each draught; a diagram with measurements of the winter, summer, tropical & freshwater load-line with a diagram of the position of the deck line; this is generally placed alongside the deadweight & displacement scale so that the deadweight or displacement can be found for any load-line at a glance; grain & bale capacity of all cargo spaces in cubic feet(ft³) or cubic metres(m³) & the position of the centre of gravity of the space; bale capacity of all cargo spaces in cubic feet(ft³) or cubic metresmetres(m³) ; capacity in cubic metres & tonnes of double bottom tanks, peak tanks, deep tanks & fuel tanks & the positions of the centre of gravity of these spaces; capacity of all stores & refrigerating chambers.

It would be difficult & inconvenient to gather all this information & place them on one plan in a clear & legible manner. In addition, all these pieces of information can be found on various other drawings. To avoid repeating data & multiplying existing documents it is instructed to create a Capacity Plan as a set of the documents listed below:

1. General Part

2. Coordinate System

3. Draught Marks

4. Load Line Mark and Deadweight Scale

5. Tank Space Information

6. Cargo Space Information