The Complete Guide to Crane Retrofits and Maintenance: Implementation Plans from Structural Reinforcement to Electrical Upgrades

After 5 to 10 years of operation, factors such as structural fatigue, electrical system aging, and regulatory upgrades make retrofitting a more cost-effective option than replacing the entire crane. The cost of replacing a 50-metric-ton overhead crane ranges from approximately 800,000 to 1.5 million yuan, whereas retrofitting a crane of the same class costs only 200,000 to 500,000 yuan. In recent years, crane safety standards have continued to be updated. GB/T 28264-2017 mandates the installation of safety monitoring systems, and TSG Q7016 imposes stricter installation and acceptance requirements for older equipment, driving significant demand for the retrofitting of existing cranes.

Structural Reinforcement and Renovation

Structural reinforcement is the most common type of crane retrofit, primarily addressing three issues: excessive downward deflection of the main girder, localized fatigue cracks, and insufficient load-bearing capacity. When the downward deflection of the main girder exceeds L/1500 (the lower limit of service camber), camber restoration or reinforcement must be performed. Common reinforcement solutions include: strengthening the main girder’s lower flange with gusset plates (adding 6–10 mm of thickness, which can restore 10–20 mm of camber), adding longitudinal stiffeners to the web (to improve local buckling performance), and welding reinforcement plates to the end girder connection zones. Welding reinforcement shall be performed in accordance with the GB/T 50661 standard, and a 125% static load test must be conducted after reinforcement to verify compliance.

Process for Controlling Welding Deformation in Large-Span Custom CranesThe methods for counter-deformation and stress relief described above are equally applicable to structural reinforcement welding. Modifications to increase the rated lifting capacity (e.g., from 16 t to 20 t) involve verifying the strength of the main girder and re-checking the load-bearing capacity of the end beams and wheel sets. According to GB/T 3811 requirements, the stress ratio of the main girder after the load increase must not exceed 0.85. Finite element analysis is an essential step in load-increase retrofits; the scope of reinforcement and plate thickness are determined after item-by-item verification under three operating conditions. Following the load-increase retrofit, type testing must be conducted again under TSG supervisory inspection. Krude Heavy Industry has completed retrofits on multiple bridge cranes, increasing their capacity from 16 metric tons to 20 metric tons and from 20 metric tons to 32 metric tons, all of which have passed TSG acceptance inspections.

Electrical System Upgrade

Older cranes typically use wound-rotor motors combined with cam controllers and relay-based logic control, resulting in poor speed regulation, high energy consumption, and a high failure rate. The electrical upgrade plan is divided into three levels: Basic Level (replacing the motor with an induction motor, adding a variable-frequency drive and PLC control, while retaining the original master controller); Standard Level (full replacement with variable-frequency speed control, PLC, touchscreen, and PROFINET communication), and Smart Level (adding an IoT gateway, OPC UA data upload to the cloud, and mobile remote monitoring to the above configuration). The cost of a Basic Level retrofit is approximately 50,000 to 120,000 yuan, with a payback period of 8 to 14 months.

Regarding PLC programming and automation interface design for non-standard crane control cabinets,Article on Building Custom Crane Control CabinetsA detailed plan has been provided. The core of the electrical upgrade is the redevelopment of the PLC program, which involves tuning the inverter parameters and programming the logic interlocks for the three mechanisms: hoisting, main travel, and trolley. The safety circuit must be redesigned in accordance with GB/T 5226.1-2019, including emergency stop, limit switch interlocks, and zero-position protection. All aging cables were replaced with flame-retardant cables (ZC-YJV), and the control cabinets were equipped with an IP54 protection rating. Following the electrical system upgrade, the hoisting speed was increased from 8 m/min to 12 m/min (VFD control), resulting in energy savings of 25% to 35%.

Installation of Safety Devices

In accordance with the requirements of GB/T 28264-2017, “Safety Monitoring and Management System for Lifting Machinery,” cranes manufactured or retrofitted after 2017 must be equipped with a safety monitoring system. When retrofitting older cranes, the following must be installed simultaneously: load limiters (110% for overload warning, 120% for shutdown), travel limit switches (for main girder/trolley/ hoist—all three directions), anti-collision devices (laser or infrared anti-collision systems must be installed when multiple cranes operate on the same track), and an anemometer (for outdoor cranes, triggering an automatic alarm when wind speed exceeds 15 m/s). The cost of installing a complete safety monitoring system ranges from approximately 30,000 to 80,000 yuan.

For special applications such as metallurgy and chemical processing, wind-resistant and anti-slip devices (track clamps or anchoring devices), explosion-proof electrical equipment (Ex d IIB T4 certified), and interlock protection devices must also be installed. After the safety devices are installed, each must undergo functional verification: limit switches must activate at a distance of ≥200 mm from the limit position, and overload limiters must reliably stop the hoist within the rated load range of 110% to 120%. Records of the functional tests for all safety devices shall form part of the retrofit acceptance documentation.

Renovation Process and Acceptance Requirements

The standard process for crane retrofitting consists of four phases: Inspection and Assessment (1–3 days) → Design (3–7 days) → Construction (7–20 days) → Inspection and Acceptance (2–5 days). During the inspection and assessment phase, measurements of the main girder’s camber, non-destructive testing of welds, wall thickness measurements, and electrical insulation tests must be completed, and an inspection report must be issued. During the design phase, reinforcement drawings and electrical schematics are developed based on the inspection findings, and the construction plan is finalized after verification via finite element analysis (FEA). The construction phase is carried out in accordance with the design drawings and construction specifications; critical processes (welding, wiring) may only proceed after passing inspection and verification.

Regarding the full process for load testing and TSG acceptance after renovation,Article on the Installation, Commissioning, and TSG Acceptance of Non-Standard CranesFor reference. Inspection and acceptance following the retrofit shall be conducted in accordance with GB/T 5905-2012 “Specifications for Testing Cranes” and TSG Q7016-2016. 125% static load test (residual deformation of the main girder ≤ L/2000) + 110% dynamic load test (3 cycles over full travel) + verification of safety device operation (testing of all functions). The modified crane must be registered for inspection with the local Special Equipment Supervision and Administration Department within 30 days; it may only be put into service after obtaining a certificate of compliance.

Comparison of the Three Major Renovation Types

Frequently Asked Questions (FAQ)