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Structural Installation Quality Control Procedure

Standard operating procedure for quality control of structural installations including gantry towers, CTPT structures, and associated components ensuring structural integrity, proper alignment, electrical safety, and compliance with relevant Indian and international standards.

System Type: Structural Quality Priority: Critical Validity: All Substation & Transmission Projects
1

Objective

To establish a comprehensive quality control procedure for the installation of structural components such as gantry towers and CTPT (Current Transformer/Potential Transformer) structures, ensuring structural stability, proper alignment, load-bearing capacity, and overall safety through standardized inspection methods in accordance with Indian Standards (IS Codes) and international best practices.

2

Code References

Code Description Application
IS 800:2007 General Construction in Steel - Code of Practice General steel structure design & installation
IS 802 (Parts 1-3) Use of Structural Steel in Overhead Transmission Line Towers Transmission tower structures
IS 7215:1974 Tolerances for Fabrication of Steel Structures Fabrication tolerances
IS 4759:1996 Hot-dip Zinc Coatings on Structural Steel Galvanization requirements
IS 5613:1985 Code of Practice for Design, Installation and Maintenance of Overhead Power Lines Overhead line structures
IS 2062:2011 Hot Rolled Medium and High Tensile Structural Steel Material specifications
IS 456:2000 Plain and Reinforced Concrete - Code of Practice Foundation design & construction
IS 1893:2016 Criteria for Earthquake Resistant Design of Structures Seismic design considerations
IEEE 693 Recommended Practice for Seismic Design of Substations Substation structure design
IS 875 (Parts 1-5) Code of Practice for Design Loads for Buildings and Structures Load calculations
IEC 61936-1 Power Installations Exceeding 1 kV AC - Common Rules Electrical clearances & safety
3

Materials & Equipment

A
Structural Components
  • Gantry tower main columns and beams (hot-dip galvanized)
  • Cross bracings and wind bracings
  • CTPT supporting structures
  • Lattice structures and beam sections
  • Anchor bolts and foundation bolts
  • Steel plates and connecting elements
  • Clamps and fixtures for equipment mounting
  • Structural grade nuts, bolts, and washers
IS 2062:2011 IS 4759:1996
B
Equipment & Accessories
  • Current Transformers (CTs) and mounting accessories
  • Potential Transformers (PTs) and mounting accessories
  • Insulators and insulator strings
  • Bus-bars and conductors
  • Earthing materials (flats, wire, connectors)
  • Terminal connectors and clamps
  • Lightning arresters (if applicable)
  • Cable trays and cable support structures
IEC 61936-1
C
Installation Tools & Equipment
  • Cranes and hoisting equipment
  • Scaffolding and work platforms
  • Torque wrenches (calibrated) for bolt tightening
  • Plumb bobs, spirit levels, and theodolites
  • Measuring tapes, rulers, and laser distance meters
  • Welding machines and accessories (if required)
  • Impact wrenches and drilling equipment
  • Personal protective equipment (PPE)
  • Safety harnesses and fall protection equipment
D
Testing & Measurement Instruments
  • Total station for alignment checks
  • Digital angle finder and inclinometer
  • Ultrasonic bolt tension meter (if applicable)
  • Coating thickness gauge for galvanization checks
  • Earth resistance tester
  • Vernier calipers and micrometers
  • Cable height meters for clearance verification
  • Digital multimeter and insulation testers
4

Pre-Installation Inspection

A
Foundation & Civil Works Check
  • Verify foundation dimensions as per approved drawings
  • Check concrete strength test reports (min. 28-day strength achieved)
  • Verify anchor bolt positions, projections, and alignment
  • Check foundation levelness (max. deviation ±3mm across foundation)
  • Verify foundation-to-foundation center distances
  • Check for any honeycomb, cracks, or damage in foundation
  • Verify foundation bolts are clean and threads are undamaged
  • Check proper curing of concrete foundations
IS 456:2000
B
Material Inspection
  • Check material test certificates for all structural components
  • Verify galvanization quality:
    Min. zinc coating thickness (610 g/m² for severe exposure) Adherence test as per IS 2629 Visual inspection for uniformity
  • Check dimensional accuracy of structural elements
  • Verify bolt grades and markings (typically 8.8 grade or as specified)
  • Check for transport damage, bending, or deformation
  • Verify material identification and traceability
  • Check condition of CT/PT and associated equipment
  • Verify completeness of all components as per bill of materials
IS 4759:1996 IS 2062:2011
C
Drawing & Documentation Review
  • Verify approved structural drawings are available
  • Check equipment layout and electrical clearance drawings
  • Review foundation drawings and bolt layout plans
  • Check assembly sequence and erection methodology
  • Verify bolt tightening torque specifications
  • Review grounding/earthing layout and details
  • Check for special instructions from manufacturers
  • Verify approved vendor documents for equipment
D
Site & Safety Preparation
  • Verify site accessibility for cranes and heavy equipment
  • Check temporary power supply for tools and equipment
  • Verify proper storage area for structural components
  • Review and approve lifting and rigging plan
  • Verify all safety equipment is available and functional
  • Check location of underground services before heavy equipment positioning
  • Verify work permits and safety protocols
  • Check weather forecast for installation period
5

During Installation Inspection

A
Structural Assembly & Erection
  • Verify pre-assembly of components on ground as per drawings
  • Check proper use of lifting equipment and safe lifting practices
  • Verify correct orientation and position of each component
  • Monitor verticality during erection:
    Max. tolerance of 1:1000 for vertical members Use plumb bob and theodolite for verification
  • Verify temporary bracings/supports during erection
  • Check progressive alignment of structure
  • Verify proper handling to avoid damage to galvanizing
  • Monitor assembly sequence as per methodology
IS 800:2007 IS 7215:1974
B
Bolting & Connection Verification
  • Verify correct bolt grade, length, and diameter
  • Check installation of washers and lock nuts as specified
  • Monitor bolt tightening process:
    Use calibrated torque wrench Apply proper torque as per specifications Follow tightening sequence if specified
  • Check alignment of connecting holes and members
  • Verify full engagement of threads (min. 3 threads showing)
  • Mark bolt heads after final tightening
  • Verify foundations bolts tightening and grouting
  • Check connection plates for proper contact and fit
IS 4000:1992
C
Equipment Installation & Mounting
  • Verify proper handling and lifting of CT/PT equipment
  • Check mounting surface preparation and cleanliness
  • Verify equipment orientation as per drawings
  • Check proper installation of insulators and support structures
  • Verify tightening torque of equipment mounting bolts
  • Check levelness of mounted equipment (max. deviation 0.5°)
  • Verify proper alignment with connecting equipment
  • Check terminal connections and tightness
IEC 61936-1
D
Earthing & Safety Systems
  • Verify installation of earthing connections to structure
  • Check continuity of earthing system
  • Verify earthing of equipment as per drawings
  • Check installation of anti-climbing devices (if applicable)
  • Verify warning/danger signs installation
  • Check proper connection of shield/earth wires
  • Verify lightning protection system installation
  • Check step and touch voltage protection measures
IS 3043:2018
6

Post-Installation Inspection & Testing

A
Dimensional & Alignment Checks
  • Verify final verticality of structures:
    Max. deviation of 1:1000 from vertical Use theodolite or total station for verification
  • Check levelness of horizontal members (max. deviation 1:500)
  • Verify center-to-center distances between structures
  • Check heights of equipment mounting points
  • Verify phase-to-phase and phase-to-ground clearances
  • Check overall dimensions against approved drawings
  • Verify alignment of bus bars and conductors
  • Check for any deformation or distortion in structure
IS 802:1995 IS 7215:1974
B
Bolting & Connection Verification
  • Perform 100% visual inspection of all bolted connections
  • Check torque verification on 10% of critical bolts
  • Verify all lock nuts and lock washers are properly installed
  • Check for any missing bolts or loose connections
  • Verify foundation bolt grouting and finishing
  • Check for proper thread engagement of all bolts
  • Verify tightening marks are aligned
  • Check for any bolt or nut damage during installation
C
Electrical & Grounding Tests
  • Measure earth resistance of complete structure (<1 ohm)
  • Perform continuity tests between structure and earth grid
  • Check continuity between different parts of structure
  • Verify correct polarity of CT/PT connections
  • Perform insulation resistance tests on CT/PT
  • Check secondary winding resistance of transformers
  • Verify CT ratio tests if required
  • Perform functional checks of measuring circuits
IS 3043:2018 IEC 60044
D
Surface Finish & Protection Check
  • Inspect for any damage to galvanization during installation
  • Verify application of touch-up zinc paint on damaged areas
  • Check for any sharp edges or potential safety hazards
  • Verify correct application of anti-corrosion compounds at interfaces
  • Check installation of protective caps on exposed bolt threads
  • Verify sealing of foundation interface against water ingress
  • Check for any foreign material or debris left on structure
  • Verify all temporary marks and tags are removed
IS 4759:1996
7

Testing Methods for Structural Installations

Test Method/Standard Acceptance Criteria
Vertical Alignment Theodolite/Total Station Max deviation 1:1000 from vertical
Horizontal Alignment Digital Level/Laser Level Max deviation 1:500 from horizontal
Bolt Torque Verification Calibrated Torque Wrench Within ±5% of specified torque value
Galvanization Thickness Magnetic Thickness Gauge Min. 86 μm (610 g/m²) for severe exposure
Earth Resistance Earth Tester (Fall of Potential Method) <1 ohm for substation structures
Electrical Clearance Direct Measurement/Laser Distance Meter As per IEC 61936-1 based on voltage level
Foundation Anchor Bolt Check Visual + Torque Verification No movement after final tightening
CT/PT Ratio Test CT/PT Test Kit Within ±0.5% of specified ratio
Insulation Resistance 5 kV Megger Min. 1000 MΩ for new equipment
8

Common Defects & Remedial Measures

Defect Possible Cause Remedial Measure
Structure Out of Plumb Improper erection, foundation settlement Re-level using shims, check foundation, adjust anchor bolts
Loose Bolts Improper tightening, vibration, missing lock washers Re-tighten to specified torque, add lock washers/nuts if missing
Galvanization Damage Improper handling, tool impact, welding Apply zinc-rich paint, inspect extent of damage, replace if severe
Misalignment of Equipment Improper mounting, support distortion Adjust mounting, check structure deformation, realign
High Earth Resistance Poor connections, inadequate earthing Improve connections, add earth electrodes, check joint resistances
Structural Deformation Overloading, impact during installation Assess structural integrity, replace damaged members
Insufficient Clearances Design error, installation deviation Reposition equipment, modify structure if required
Foundation Bolt Misalignment Template error, shifting during concreting Use slotted base plates, reposition if possible
9

QA/QC Checklist for Structural Installation

  • All approved drawings and specifications available on site
  • Foundation dimensions, levels and anchor bolt positions verified
  • Material test certificates and galvanizing reports checked
  • Proper storage and handling of structural components
  • Structure assembled and erected in correct sequence
  • All bolts of correct size, grade and properly tightened
  • Verticality and alignment within permissible tolerances
  • Electrical clearances verified as per standards
  • Equipment properly mounted and aligned
  • Earthing connections complete and tested
  • CT/PT orientation and polarity checked
  • Surface finish inspection and touch-up completed
  • No temporary fittings, tools or debris left on structure
  • All safety signs and anti-climbing devices installed
  • Complete documentation including test reports compiled
10

Acceptance Criteria

Dimensional Accuracy: Within ±5mm for critical dimensions, overall dimensions within ±10mm
Verticality: Maximum deviation of 1:1000 from vertical
Levelness: Maximum deviation of 1:500 for horizontal members
Bolt Tightening: All bolts tightened to specified torque (±5% tolerance)
Electrical Clearance: As per IEC 61936-1 based on system voltage level
Earth Resistance: <1 ohm for complete earthing system
Surface Protection: No significant damage to galvanization, touch-up completed
CT/PT Performance: Ratio accuracy within ±0.5%, insulation resistance >1000 MΩ
IS 800:2007 IS 7215:1974 IEC 61936-1
11

Important Safety Considerations

  • Mandatory use of PPE including hard hats, safety shoes, and harnesses
  • Verification of electrical isolation before working on connected structures
  • Proper fall protection systems for heights exceeding 1.8m
  • Certified lifting equipment and rigging with valid inspection
  • Suspend outdoor work during adverse weather (high winds, storms)
  • Special precautions for work in extreme temperatures
  • Proper barricading of work areas with warning signs
  • Use of proper tools and equipment for height work
  • First aid kit and emergency contact information available
  • Buddy system for all elevated work activities
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