SHIP MATERIALS

Magnetic P Advantages Simple and easy to conduct. Will detect surface and near surface flaws. Can detect flaws filled with contaminants e.g. oxide or non metallic inclusions. Can be fixed or portable equipment, Instant repeatable results Large surface area or large volume of parts/ materials can be inspected rapidly at low cost. (Economical)

Particle Testing Disadvantages Can only be applied to ferromagnetic materials. Will not detect deep internal flaws. High currents applied to component may cause damage. Components usually have to be demagnetized. Requires multiple operations under controlled conditions. 21

Radiograph ❑ Radiographic inspection or testing (RT based on using short wavelength elec material. ❑ The part is placed between the radiatio stop some of the radiation. ❑ Materials with areas of reduced thicknes therefore absorb less, radiation. Thicker radiation ❑ The film darkness (density) will vary wit through the test object. ❑ The radiation, which reaches the film a shadow image on a photographic film (ra

hic Testing T) is a non-destructive inspection method ctromagnetic radiation passing through the on source and a piece of film. The part will ess or lower material density allow more, and r and more dense sections stop more of the th the amount of radiation reaching the film after passing through the material, fo22rms a adiograph).

Radiographic

c Testing - images 23

Radiographic Te The p sourc some dense X-ray film Top view of developed film

esting - Principle part is placed between the radiation ce and a piece of film. The part will stop e of the radiation. Thicker and more e area will stop more of the radiation. The film darkness (density) will vary with the amount of radiation reaching the film through the test object. = less exposure = more expos24ure

Radiogra -General

aphic Testing arrangement- 25

Radiograph -Appearance of film

hic Testing m after development- 26

Radiogra -Welded

aphic Testing Component- Gas Porosity and Gas Holes 27

Radiograph -Pressure The failure of a pressure vesse can result in the rapid release of a large amount of energy. To protect against this dangerous event, the tanks are inspected using radiography and ultrasonic testing.

hic Testing Vessel- el a t e g 28

Radiogra Advantages Can be used to inspect virtually all materials Detects surface and subsurface defects. Ability to inspect complex shapes and multi-layered structures without disassembly. Minimum part preparation is required. Permanent record Good quality control method

aphic Testing Disadvantages Extensive operator training and skill required. Access to both sides of the structure is usually required. Orientation of the radiation beam to non-volumetric defects is critical. Field inspection of thick section can be time consuming. Relatively expensive equipment investment is required. Radiation hazards 29

Ultrason Ultrasonic testing involves the use of high passing through the component part bein discontinuities, and related faults. The method is used to detect, and locate ferrous and non-ferrous metals. The procedure can also be used to meas Ultrasonic examinations can be conduc including castings, forgings, welds, and c

nic Testing h frequency sound waves or vibrations ng inspected for surface defects, e defects and establish their size in both sure material thickness. cted on a wide variety of material forms composites. 30

Ultrasoni High frequency sound waves are introduc back from surfaces or flaws. Reflected sound energy is displayed versu cross section of the specimen showing th initial back surface pulse echo crack echo 0 2 4 6 8 10 Oscilloscope, or flaw detector screen

ic Testing ced into a material and they are reflected us time, and inspector can visualize a he depth of features that reflect sound. crack plate 31

Ultrasonic T UT inspection system : Pulser/ Receiver, T Pulser / Receiver : Electronic device to pro High frequency ultrasound is generated w The transducer is capable of both transmitting and receiving sound energy.

Testing - Devices Transducer, Display Device oduce electrical pulse with a transducer. A piezoelectric element in the transducer converts electrical energy into mechanical vibrations (sound), and vice versa. 32

Ultrasonic T Test Specimen Display Device

Testing - Devices Transducer Pulser/Receiver 33

Ultrasonic Te ❖ High frequency sound wave transducer. ❖ The sound waves travel throu same transducer or a second ❖ The amount of energy tran energy is received are analyz ❖ Changes in material thickne can also be measured.

esting - Principle es are sent into a material by use of a ugh the material and are received by the d transducer. nsmitted or received and the time the zed to determine the presence of flaws. ess, and changes in material properties 34

Ultrasonic Testi ❖ One of the most widely used methods of inspecting weldments is ultrasonic inspection. ❖ Full penetration groove welds lend themselves readily to angle beam shear wave examination.

ing – Flaw Detection 35

Ultrasonic Tes ❖ Can detect surface and subsurface fla ❖ Depth of penetration for flaw detect methods. ❖ Access to only one side required when ❖ High accuracy in determining reflector ❖ Minimal part preparation required, por ❖ Electronic equipment provides instant ❖ Detailed images can be produced with ❖ Has other uses such as thickness mea ❖ Volumetric inspection. ❖ Inspects a variety of thicknesses and w ❖ Non-hazardous to personnel. ❖ Suitable for automation.

sting - Advantages aws. tion or measurement is superior to other n pulse-echo technique is used. r position and estimating size and shape. rtable equipment taneous results. h automated systems. asurements, in addition to flaw detection. weld types. 36

Ultrasonic Tes ❖ Surface must be accessible to trans ❖ Skill and training is more extensive ❖ Normally requires a coupling mediu into test specimen. ❖ Materials that are rough, irregular i or not homogeneous are difficult to ❖ Cast iron and other coarse grained low sound transmission and high sig ❖ Linear defects oriented parallel to th ❖ Reference standards are required characterization of flaws. ❖ Test surface must be smooth. ❖ Expensive equipment. ❖ Reference standards required. ❖ Results require interpretation by exp ❖ Inspection of welds over 6 mm thick

sting - Limitations smit ultrasound. than with some other methods. um to promote transfer of sound energy in shape, very small, exceptionally thin inspect. materials are difficult to inspect due to gnal noise. he sound beam may go undetected. d for both equipment calibration, and perienced person. 37 k.

Eddy Cur ❖ Eddy current inspection is one of principal of “electromagnetism examinations. ❖ Eddy currents are created throug induction. When alternating curre as copper wire, a magnetic field de This magnetic field expands as maximum and collapses as the cu ❖ Eddy currents are induced electr path

rrent Testing f several NDT methods that use the m” as the basis for conducting gh a process called electromagnetic ent is applied to the conductor, such evelops in and around the conductor. s the alternating current rises to urrent is reduced to zero. rical currents that flow in a circular 38

Eddy Curre Coil Eddy currents

ent Testing Coil's magnetic field Eddy current's magnetic field Conductive material 39

Eddy Curr In the proper circumstances, eddy ❑ Crack detection. ❑ Material thickness measurem ❑ Coating thickness measureme ❑ Conductivity measurements fo ✓Material identification ✓Heat damage detection ✓Case depth determination ✓Heat treatment monitoring

rent Testing y currents can be used for: ments. ents. or: 40

Eddy Curre Schematic of magnetic flow in eddy current testing

ent Testing Devices use in eddy current testing 41

Eddy Cur Small surface probe is scanned over th crack.

rrent Testing he part surface in an attempt to detect a 42

Eddy Current Tes ❑ Sensitive to small cracks and oth ❑ Detects surface and near surface ❑ Inspection gives immediate resul ❑ Equipment is very portable ❑ Method can be used for much mo ❑ Minimum part preparation is requ ❑ Test probe does not need to cont ❑ Inspects complex shapes and siz

sting - Advantages her defects e defects lts ore than flaw detection uired tact the part zes of conductive materials 43

Eddy Current Te ❑ Only conductive materials can be ❑ Surface must be accessible to the ❑ Skill and training required is more ❑ Surface finish and roughness may ❑ Reference standards needed for s ❑ Depth of penetration is limited ❑ Flaws such as delaminations that and probe scan direction are unde

esting - Limitations inspected e probe e extensive than other techniques y interfere setup lie parallel to the probe coil winding etectable 44

CHAPTER 7 CORR

ROSION IN SHIPBUILDING