Inspection, Maintenance of Lifting Machine for Safe Lifting Operations

Lifting machines are often used in workplaces. The variety of lifting machines and its capacity and operation characteristic was carefully chosen for mobilization. Often, incident involving lifting machines result in drastic outcomes which affects multiple stakeholders and their next-of-kin. The impact of not regularly maintaining and inspecting can contribute to a fragment of contributing causes where mechanical failure aspect is at large. Brainstorming on the possible contributing causes which may result in the crane jib buckling, many will have doubts on maintenance portion. Crane manufacturers have demonstrated high consideration importance during designing of cranes, focusing on the crane jib / boom bending and torsional stiffness along with the reduction of mass, and the quality of its parts to serve the industry better.

Structural integrity

Structural integrity is the ability of a structure to withstand its intended loading without failing due to fracture, deformation, or fatigue. It is a concept often used in engineering to produce items that will serve their designed purposes and remain functional for a desired service life.

Fatigue Stress

A crane jib / boom bears various loads in multiple directions, which may include its own mass of boom, wire ropes, hook blocks, lifting gears, material load, wind load and any fly jibs. Torsional bending buckling tests can be carried out regularly on machines with massive usage round the clock. Stress-strain analysis and Scanning Electron Microscope (SEM) methods can be adopted to identify fracture surface. To do a thorough inspection of metal parts, wire ropes or any lifting gears (made of metal), the macroscopic survey as well as the metallographic testing can be considered. Superficial identification of damages can be detected by visual inspection.

But to further determine the structural integrity strength and impacts of fatigue stress on the structure, only metallographic examinations can assess it. Wire ropes loaded with high tensile force on winch drums, pulleys and on cable drums may have high possibilities of outer damage due to massive times of repetitive strains. Accelerated fatigues are caused by un-identified damages during visual inspection, mis-use of lifting equipment, poor maintenance. Such deteriorations will increase the load burden on the remaining undamaged parts, which will eventually result in a sudden bending of boom or wire snap, when it has reached its optimum tolerance.

Vulnerable slender crane parts

Latent failure can occur during severe corrosion of connect bolts. Crane is made up of small portions and connected by bolts e.g. joint of boom sections , crane chassis and slewing table. Insufficient of heat treatment in manufacturing the bolts as classified as the main reason for fatigue fracture failure. Workplace actual practice may differ with specifications in crane manual e.g. set screws with / without washer, use of corroded connection component, use of illegitimate bolts as replacement.

Mast anchors of tower crane foundations were not inspected or tested prior to erection of the tower crane. In previous cases, the expert witnesses for the plaintiff and for the defendant were in agreement as to the cause of the tower crane’s collapse. They also agreed that the party responsible for the lapse leading to the collapse was the third party and that the defective mast anchors had pre-installation cracks and could have been inspected and tested even after installation as they were all erected above ground level.

Fatigue lifespan

Fatigue in mechanical properties, welded joints is named a common cause to failure. Calculating the remaining fatigue life of structure is made possible through experimental testing with method associated with finite element analysis to measure the crack growth from an initial to a critical value leading to a fracture. Fractography assessment of fatigue and forced fractures can be carried out on welding joints.

Competency of maintenance personnel

Maintenance personnel shall be trained, certified and competent by training from vocational institutes, crane manufacturers. Approved crane erector approval by governing authority for such personnel is also a must, before he / she is allowed to carry out any erection, alteration, dismantling and maintenance on crane. Appointing such competent maintenance personnel involve critical selection and evaluation criteria. Manufacturer's training for maintenance personnel is the most critical element compared to vocational training and crane erector approval, as the manufacturer's specific product inspection & maintenance training enhance the familiarization of maintenance personnel.

Failure of a lifting machine

Majority of the failure of lifting machine are either due to Human error or Mechanical failure. Possible failure of a crane which may be categorized into seven main parts namely:

1. Ground foundation

• Prior soil test results (e.g. Type / Category of soil)
• Type of Crane and its mass weights and dimensions (e.g. Load of crane and its parts, accessories and counterweights, Length & Width of crawler tracks)
• Ground bearing engineering design (varies on different environment scenarios) and is dependent on the load bearing pressure
• Footing and Ground condition inspection and recorded by designated person after inclement weather
• Insufficient rigidity of outriggers (Functional failure)
• Outriggers sitting near excavated trenches or Temporary earth retaining structures

Crane structural integrity

• Corrosion
• Welding joint
• Bending & Torsional Stress
• Fatigue stress
• Wind load on slender parts
• Lifespan of fatigue

Slinging stress

• Selection of suitable lifting gears
• Height, Length, Width and Weight of load to hoist
• Understanding of Gross and Net weight
• Understanding of safety factor of lifting gears for different angle
• Material handling planning 

Man and associated hazards

• Fatigue due to long duration of work
• Ergonomic issues due to awkward work position
• Pre-existing medical conditions
• Incompetency to carry out Pre-use inspection
• Working in an unsafe manner due to tight deadline
• Incompetent maintenance personnel
• Pendulum effect leading to overloading due to dragging or fast swing of load 

Corporate / Organization

• Workplace Safety and Health culture
• Workplace Safety and Health Risk Management
• Workplace Safety and Health investment
• Workplace Safety and Health leadership
• Psychological Safety
• Policies and procedures must be clear and precise on strict adherence to Workplace Safety and Health expectations
• Contract agreement to encompass all recommended maintenance and testing

Environment

• Lifting path planning, identification of overhead and adjacent obstructions
• Crane traffic route, Workplace Crane Access route
• Sufficient amount of lighting
• Work area prone to thunderstorm, lightning, strong winds
• Possibility of collision during crane swing radius
• Demarcation to prevent unauthorized entry into lifting zone
• Identification of railway zones (above ground / underground), underground services e.g. drains, manhole, electrical and sewer services

Materials

Main parts and accessories of a crane shall always use only original manufactured ones, batch testing frequency of such products must be as regular as possible.

Method

Rigging method are very important in a lifting plan. A simple understanding of the load factor according to the rigging method differs. A precise sketch and calculation within the lifting plan for each and every load that is required to be lift by a lifting machine should have its range of lifting gears and / or accessories, rigging method, calculations reflected.

Crane stability

Cranes can gain stability by tipping the axis. The relationship between the sufficient load mass, the boom angle, its radius and the load's center of gravity is stability.

Differences within items of daily crane operator pre-use checks and crane erectors checks

The involvement and participation of Approved Crane Contractor, Manufacturer's Technical personnel is very critical to formulate a precise, in-depth and comprehensive checklist for all lifting personnel to utilize, instead of a generic one.

Complex & Heavy lift

• Shipment inventory forecasting
• Traffic route pre-survey, Crane Access route ground engineering design, Preliminary lifting height and reachable limit site assessment
• Lifting using quay / port cranes
• Load transfer - Jacking operations
• Transportation by Self Propelled Module Transporter (SPMT)
• Traffic escorts
• Tandem lifts for module launching / installation
• Pre-mobilization of lifting machine thorough inspection & maintenance by manufacturer / crane supplier
• Use of Adjustable Module Lifting Frame (AMLF), Spreader Beam

This article does not conclude any findings of any MOM investigation. This is purely from the sharing of author's discretion with a rationale to let interested parties have more understanding on the possible hazards within manufacturing to usage and maintenance processes of a crane, and how we can do our utmost effort maintaining a Safe Workplace.