Module 7.18 Disassembly, inspection, repair and assembly techniques (incl. NDT)

Knowledge levels

Item	A	B1 / B3	B2 / B2L
7.18(a) Types of defects and visual inspection; corrosion removal, assessment and re-protection	2	3	3
7.18(b) General repair methods, SRM; ageing, fatigue and corrosion control programmes	—	2	—
7.18(c) NDT: penetrant, radiographic, eddy current, magnetic particle, ultrasonic, borescope (incl. practical colour-contrast penetrant)	—	2	1
7.18(d) Disassembly and reassembly techniques	2	2	2
7.18(e) Troubleshooting techniques	—	2	2

Types of defects

Defect	Description
Crack	separation of material - fatigue, overload, stress corrosion
Dent	depression with smooth edges, no loss of material
Nick / gouge / scratch	sharp-edged damage with displaced or removed material - stress raiser
Scoring	deep scratches from foreign particles between moving parts
Corrosion	electrochemical attack (Module 6.4)
Brinelling, galling, fretting, spalling	bearing and contact surface damage
Burning / heat damage	discolouration, loss of temper
Buckling, distortion, elongation of holes	overload
Erosion	material worn away by particles/fluid flow
Delamination / disbond	composites

Visual inspection

• The most widely used method. Aids: good lighting (torch at a low angle to show surface irregularities), magnifying glass (5-10×), mirrors, borescopes.
• Clean the area first; know where to look (stress concentrations, fastener rows, fillets, drain areas).
• Levels: general visual inspection (GVI) from within touching distance with normal lighting; detailed visual inspection (DET) - intensive, with aids, possibly surface cleaning; special detailed inspection (SDI) - may need NDT or disassembly.