technical of SHACKLESS & CLEVIS
1. Ultimate Tensile Strength (UTS)
1. UTS of shackles and clevises depends on design, size, and material (typically forged steel or ductile iron):
I. Small distribution line hardware: UTS ~ 45–70 kN
II. Medium transmission line hardware: UTS ~ 70–120 kN
III. EHV lines (220–400 kV): UTS ~ 120–160 kN
2. Tested according to IEC 61284 / IS 2486 / ANSI C135.
2. Working Load / Safe Working Load (SWL)
1. Typically taken as 1/2.5 or 1/3 of UTS, depending on application and design factor:
I. For a 120 kN UTS clevis or shackle, SWL = 40–48 kN
2. Ensures safe long-term use under conductor tension, wind, and ice loading.
3. Conductor Diameter Compatibility
1. Shackles/clevises connect conductors or insulators indirectly through clamps, thimbles, or pins.
2. Typical hardware is compatible with fittings designed for conductor diameters from 10 mm to 40 mm.
3. Mounting holes and jaw openings are standardized (e.g., 16 mm, 20 mm, 24 mm) to ensure universal compatibility with other hardware.
4. Slip Strength:
1. Refers to slip resistance at the pin-joint or contact interface, preventing loosening under load.
2. Bolt/pin connections with cotter pins, split pins, or threaded nuts ensure secure locking.
3. Rated slip resistance is generally >80–90% of UTS, i.e., 70–150 kN for EHV-grade clevises.
5. Temperature Withstanding Capacity:
1. Operable in extreme environments: –40°C to +85°C continuous.
2. No deformation under conductor heating up to 90°C, and survives short-term exposure to up to 250°C during faults/arcing.
3. Metal body maintains strength across temperature range.
6. Corrosion Resistance:
1. Hot-dip galvanized to ensure >80–100 µm zinc coating thickness.
2. Galvanizing as per ASTM A153 / IS 2629, offering protection in coastal, industrial, and desert zones.
3. Some hardware also treated with passivation or epoxy primer for added protection.
7. Impact & Fatigue Strength:
1. Forged hardware provides excellent impact resistance and ductility.
2. Clevis and shackle designs are tested for vibration fatigue (10,000+ cycles).
3. Withstands mechanical shocks from line galloping, wind, or switching surges without fracture.
8. Mechanical Endurance:
1. Designed for >30 years of service life.
2. Maintains mechanical performance after thermal cycling, vibration fatigue, and repeated load/unload cycles.
3. Regular torque retention testing is done on bolts/pins.
9. Design Safety Factors:
1. Mechanical safety factor: ≥2.5 to 3.0, depending on voltage level and criticality of application.
2. For example, for a 150 kN UTS clevis, maximum working design load is ~50 kN.
3. Provides reliability during extreme environmental or fault conditions.
Top 5 Quality Assurance
1. Mechanical Testing as per Standards
a. Tested as per IEC 61284, IS 2486 (Part 1 & 2), or ANSI C135:
I. Ultimate tensile load test
II. Slip strength and bending moment test
III. Galvanizing thickness and adhesion
IV. Hardness and microstructure analysis (for forged hardware)
2. Dimensional & Visual Inspection
a. 100% check for:
I. Pin-hole alignment and tolerances
II. Surface cracks, forging flash, or pits
III. Bolt/pin threading accuracy
IV. Jaw opening and fit with mating parts
3. Corrosion Resistance & Environmental Test
I. Salt spray test (500–1000 hours) as per ASTM B117
II. Zinc coating thickness tested using electromagnetic or cross-section methods
III. Visual rust inspection post testing for life simulation
4. Raw Material & Process Control
a. Materials like mild steel, forged steel, ductile iron tested for:
I. Yield strength
II. Elongation
III. Chemical composition (via spectrometer)
b. Heat number and batch tracking enabled for every lot
5. Traceability & Certification
a. Each part stamped with:
I. Manufacturer name/code
II. Load rating or batch number
III. Size and hole dimensions
b. Supplied with:
I. Routine test reports
II. Type test certificates (CPRI/ERDA/SGS)
III. GTP, ISO 9001 / ISO 14001 certification
IV. Option for third-party inspection (by utilities or BIS-accredited agencies)