Methods for Assessing Part Condition Introduction: To evaluate the condition of parts, mechanisms, or engine elements and determine maintenance needs, thorough testing is essential during defect surveys. These tests employ physical and technological inspection methods. Physical Inspection Methods: Includes X-ray, gamma-ray, ultrasonic, magnetic, luminescent, and color tests. These methods detect defects such as slag inclusions, cavities, gas pores, and cracks in castings, forgings, welded joints, and finished articles. • • • X-ray, Gamma-ray, and Ultrasonic Inspection: Primarily used for detecting internal defects in metals. Magnetic Inspection: Identifies subsurface and surface defects. Luminescent and Color Inspection: Detects surface defects. Advantages of Physical Procedures: Relative simplicity, high sensitivity, accuracy, and the ability to detect defects without dismantling units or connections in many cases. Technological Inspection Methods: Consist of visual inspection (with varying magnification levels), dimensional measurements, chalk-kerosene and magnetic-kerosene methods, electrolytic etching, tightness tests, etc. Preliminary Operations before Defect Survey: Hull Side: • • • • • Removal of marine growth, paint, and mill scale from shell plating. Cleaning of holds. Drying, cleaning, and gas-freeing of tanks. Opening of manholes. Necessary dismantling work. Machinery Side: Dismantling and cleaning parts to remove dirt, oil, scale, deposits, corrosion products, insulation, and other substances. Understanding Wear Concepts and Terminology • Conceptual Differentiation: • Wear: Refers to two distinct concepts: 1. Progressive change in dimensions of rubbing surfaces due to friction, caused by surface particle removal or plastic deformation. 2. The process leading to wear, denoted as the "wearing process." Wearing Process: • Defined as the progressive change of surface dimensions of machine parts resulting from friction. Wear Resistance: • Indicates a material's ability to withstand the wearing process under given service or test conditions. Absolute Wear: • Reduction of weight or dimensions in wearing tests. • Can be specified by the method used for measurement, such as "by weight measurement" or "by height measurement." Linear Wear: • Wear measured by dimensional changes along the normal to the rubbing surface. Wearing Intensity: • Ratio of absolute wear of a sample (or part) in wearing tests to the path traversed during rubbing. • May be average or instantaneous if wear progression is not constant. Wearing Rate: • Ratio of absolute wear of a specimen (or part) in wearing tests to the duration of the test. • Qualifiers such as "average" or "instantaneous" indicate non-constant progress of the rubbing process. • • • • • • • Importance of Wear Assessment: • Knowledge of wear magnitude and distribution on rubbing surfaces is crucial for: • Assessing part condition before repairs. • Determining methods to inhibit the wearing process. Methods for Determining Wear Magnitude 1. Weighing Method: • Used for investigating wear in lightweight parts in laboratory conditions. • Weighing is done before and after testing using analytical or industrial balances. • Linear wear is determined by the loss in weight, assuming uniform distribution over the rubbing surface. • Unsuitable when wear results from both particle removal and plastic deformation. 2. Contamination of Lubricating Oil: • In cases where dismantling the machine is undesirable, wear can be assessed from metallic impurities in the lubricating oil. • A sample of the oil is burnt, and chemical and weight analysis determines the metallic content (wear product). • Most wear products are suspended in the oil and carried away with it. 3. Use of Radioactive Isotopes: • Wear products in the lubricant are assessed using labeled atoms or radioactive isotopes. • The metal content in the oil is measured by the intensity of radiation emitted by the radioactive element entering the oil with wear products. • Radioactive isotopes facilitate checking for wear in machine parts, determining the effects of various factors, establishing optimal working conditions, improving machinery design, and organizing maintenance routines and spare parts production. 4. Micrometric Measurements: • Wear assessment is performed using micrometers or other indicating instruments with scales. • Detects wear in various parts of the rubbing surface, including measurements with mechanical contact devices or sensitive instruments like pneumatic or contact transducers. 5. Profilography: • Provides a graphical record of wear distribution over a small part of the rubbing surface. • Measures the reduction in height of roughness peaks and recurrence of contours of troughs, revealing wear within the range of surface irregularities. The acceptance of work done on the hull in its construction or - repair, the assessment of how far the work corresponds to the requirements of the Soviet Register and the technical specifications, and also the survey of defects before repairs require tests for watertightness and continuity of contact between parts. Tests for watertightness are carried out according to the requirements of the Soviet Standard Methods and Standards for Testing Hulls, and according to Rules of Classification and Construction of Sea-Going Steel Ships of the Soviet Ship Register Tests for Watertightness of Hulls of Sea-Going or Harbour Vessels). According to these Rules and the Soviet Standard, the parts of the ship, from the point of view of testing procedures and standards, are divided into two groups: (1) ballast and other compartments which contain water under service conditions, fuel tanks, and also Kingston valve chests, cisterns, hollow rudders, and propeller (Kort) nozzles; (2) all remaining compartments, superstructures, hatch coamings, chain lockers, hawse pipes, and chain pipes. The parts of the ship belonging to the first group are tested by flooding them with water under pressure or with compressed air; those belonging to the second group are tested by completely filling them with water, or by playing a jet of water under pressure over the surface; alternatively, by wetting the seams with kerosine, or blowing compressed air over them. Using water in tightness tests, the water may be poured in or formed into a jet under pressure, or a non-pressurized stream may be used. The structure under examination is considered tight if the checked surface does not show signs of moisture, running drops, or leaks, and, in the case of tests under a head of water, the level of the water remains unchanged. In freezing weather conditions, warm water is used for pouring into the tested structures, and for pouring over seams hot water is employed. This is necessary to ensure that external surfaces of the compartments should be above freezing, that no “sweating” should occur, and that the water seeping through the cracks should not freeze. The Soviet Register permits the use of anti-freeze solutions instead of heating the water. To induce hydrostatic pressure in the flooded compartment, a pressure column (or tube) is erected on the deck which covers the compartment; this column should be at least 50 mm in diameter. Alternatively, a flexible hose of sufficient rigidity may be used. In accordance with the foregoing, the following points should be observed in tightness tests by flooding: (1) the duration of the test is determined by the time necessary for inspection, but should not be less than one hour; (2) there should be no ullage space in the flooded-compartment; (3) the pressure head should be read from the highest point in the compartment to the water level in the pressure pipe; (4) the order of flooding (every other compartment, or in chequered pattern) should take into account the consequent additional stresses in the hull and on the building berth. When the tests are done on a floating ship, the draught should not exceed the full-load draught; (5) in deck compartments where water dripping may occur (wash basins, baths, showers, kitchens, etc.) the junctions between the bulkheads and decks, and the lower parts of the bulkheads are subjected to the flooding test with the water level reaching the height of the coaming, the test lasting at least 30 mm . The test should be performed after all the piping has been installed and before plastering. Testing by water jet under pressure is done using a fire hose. The pressure should be sufficient to ensure a jet height not less than 10 m. The hose nozzle should be not more than 3 m away from the site under test. Welded seams are tested from either side, and riveted seams from the non-caulked side. Vertical seams are tested directing the jet from below upwards. Testing for tightness by compressed air is done by filling the compartment with compressed air or blowing compressed air over the tested surface with the use of a hose. The checked surface is wetted with a soap solution and if no bubbles appear during the test, the structure is considered to be tight. In freezing weather conditions, testing is done only if it is possible to heat the structure to a temperature above 0∘ C, and using a nonfreezing and noncongealing soap solution. When the ambient temperature is not less than −5∘ C, it is permissible to wet the seams with a soap solution heated to 60 − 80∘ C. The air pressure in air-flooding tests is taken as half the water pressure prescribed in the above-mentioned Soviet Standard or Rules. of the Soviet Register. If the decking is not sufficiently strong and the prescribed pressure cannot be used, the pressure should be found by calculation, taking into account that the stress in the weakest part of the structure should not exceed 0.6 of the yield point of the material. The lowest testing pressure for sea-going ships should not be less than 0.25 atm. Two manometers with safety valves are installed in the tested compartment or tank. The air is fed through a reduction valve. The duration of the test depends on the time necessary for inspection, but should not be less than 1hr. When compressed air is blown over the surface, the pressure in the air hose should not be less than 4-5 atm. The air jet is directed right against the seam, and with riveted constructions the jet is played on to the non-caulked side. The end of the hose is fitted with a nipple for the pneumatic nozzle, which should not be further than 100 mm from the seam. Surface blowing tests should be performed only in the case of short and straight seams. Contact continuity tests can be carried out for fixed or movable joints. With fixed joints (for example, between a shaft with a pressed-on sleeve) the contact test is made by tapping with a light hammer. A wooden or hollow sound will indicate discontinuity. With movable joints (e.g., between a valve plate and its seating, between a plunger valve pair, etc.) the contact can be tested using paint, kerosine or compressed air. When using paint, one part is lightly smeared with a sticky contact paint and is turned against the mating part. The imprint on the mating part shows whether correct contact is achieved. When using kerosine, there should be no leak between the mating parts. With compressed air, lack of tightness is shown by the pressure drop or air blow-by. When checking the quality of material of ships’ parts and installations, defects are found which arise in the course of manufacture and subsequent thermal treatment. Defects of this type include bright spots, sand inclusions, hair line cracks, laminations, double skin, cavities, etc. Bright spots occur in forgings and reveal themselves by a characteristic silvery lustre; in the majority of cases they take the form of thin threads and represent non-metallic inclusions which stand out in relief on a darkened acidic background when the metal surface is etched. Bright spots impair the mechanical properties and the uniformity of the structure. The presence of a large number of bright spots on the surface of such parts as rotors, shafts, disks, etc., makes their rejection necessary. Sand inclusions appear as a result of contamination of the metal by slag in the melting process. The sand particles fall out during machining, and cavities are left behind. The presence of such defects is particularly undesirable in parts which work in rubbing contact. Hair line cracks are narrow (sometimes invisible) cracks on the surface of the metal. Such defects are detected by the magnetic kerosine tests described above, or by etching the polished metal surface. In the latter case, owing to the stronger acid attack on the edges of the cracks, they become visible as thin “veins”. Laminations in the metal result from the presence of gaseous and shrinkage cavities in ingots, which have not been eliminated by rolling. This defect may be dangerous, and can be observed in fire tubes and walls of boiler furnaces. As a sign of this defect, bulges occur in the affected areas of the boiler, although no deformation is observed on the opposite side. The defects are detected by thorough cleaning of the suspected zones, examining them with a magnifying glass, and cutting out samples for tests. To find the laminations, one edge of the sample is polished and etched with a 10% solution of hydrochloric acid. The bright spots, sand inclusions, etc., are chiselled out until a depth is reached where the shavings do not show a split. Then another examination is made. Double skin in steel or cast iron parts is detected magnetically. To find internal defects in the form of cavities, laminations, etc., use is made of ultrasonic flaw detectors of various types, produced in the U.S.S.R. Timely and complete detection of defects in parts having a whitemetal lining is important, since it makes it possible to eliminate the defect and prevent the failure of the machine. When conducting a defect survey, an external examination is made, special measurements are taken, and tests and analyses are carried out. In a number of cases, to determine the character and extent of the defect in the whitemetal lining, measurements of parts in rubbing contact are necessary. To test the type of whitemetal and its conformity with technical specifications, a chemical analysis is necessary. The structure of whitemetal is found by metallographic analysis. The defects that can be found in parts having whitemetal linings (bearings, eccentric hoops, sliders, stern-tube bushings) include thickness reduction of the lining due to the wearing process, cavities, cracks, separation of the lining, fissures, scoring marks, change of structure (coarsening of the grain). Reduced thickness of the whitemetal can be found by direct measurement, or by drilling check holes which show the thickness of the lining. Pits can occur singly or in agglomeration, forming shallow rashes and pores. Pits are detected visually. Cracks can occur singly or in agglomeration, and can be on the surface or go right through. They are also detected visually. Whitemetal lining separation is detected by sound, by rebound of metal filings under impact, by chalk-kerosine testing, or by oil bubbles squeezed out when the lining is pressed on. Scratches and scores are detected visually. Structure changes are determined by metallographic examination.
