Two parallel ropes running over sheaves with an equalizer at the termination
As due to bad maintenance, the equalizer did not functioned, accordingly there was no load sahring betwen the two ropes, only one rope was sharing the load, clearly  seen by the prints on the sheaves grooves, 
 
 Recommendation:
 Always start with the sheaves, they have a lot to tell us on the rope condition. 
 
      
 
 
 Core failure in a 19*7 tower crane rope
 Non rotating ropes are sensitive and even dangerous when rotation is permitted or induced.
  
 
 
 
 
 
  
40 mm rope, IWRC, Outer strands do not show any damage, But: a total broken core inside:
dangerous situation
 
The operator assumes the rope is safe but actually its core is broken and a domino breaks process of strands will start, and finally will be ended in a broken rope
                             Failure Analysis
Wire ropes
Hoisting machine inspection and survey
 

 

The end user will expect the rope/wire rope to provide reasonable service life with safety surround. But, we are daily facing incidents at which the wire rope/rope are discarded and sometimes failed after a short service time.

Analyzing the causes for rope failure or rope fast deterioration must include all parameters which will consider the rope quality, machine parameters, practice of the operators and maintenance team.
The rope is not always to be the only accused parameter.

By means of the personal experience of Dr. Ashkenazi as a crane inspector M.R.E. provides failure analysis and machine inspection and survey in order to identify the causes for fast degradation of wire ropes, failures of ropes and wire ropes, identify critical interfaces between rope and machine components.

This service will provide the end user useful information and recommendations in order to improve safety and increase the service life of the rope and achieve an optimal compatibility between the rope and the machine.

In the following the influential parameters to be studied are listed. M.R.E is focusing on these when facing a failure analysis.

  •    Wire rope quality

The quality of the rope will directly affect the rope performance. Rope quality includes the following parameters:

- Wire/fibers quality (yarns twisting and roving, metallurgical construction, surface quality, heat treatment etc)

- Production process at the wire, strand, and rope level. These include twisting, cold drawing, and stranding, compacting and closing processes.

- Size control at the core, strand and rope level. This includes diameter control and its changing due to loads and cycling.

- Wire rope lubrication. The lubrication of the rope at the wire and strand level will strongly affect rope service life. Moreover, at specific applications the initial lubrication has a major rule with respect to the potential service life.

- Compatibility of the rope cross section with the hoisting application.

The type of the cross section has a major impact on the service life. Rope characteristics as torque factor, torsion stiffness, lay direction, filling factor and outer strand shape will strongly influence on the rope performance
 
  • Machine parameters

The machine performance and design will have a considerable impact on the rope service life and even on the safety surround. Parameters and properties which may cause fast deterioration are:

- Loading and hoisting control  The control of acceleration, starting/braking are critical with regard to the dynamic loads which are generated at the rope. Bad control will generate high level of dynamic loads, small but critical slipping of the rope at the sheave groove, lateral and axial vibrations. These will cause the initiation of fatigue cracks and will reduce the service life. Moreover, a good rope which is installed in a bad controlled machine may cause sever damage to the drums, sheaves and other components in the crane.

- Fleet angles. Bad design of drum size, sheave arrangement will cause constructional damage to the rope, these may generate fatigue and internal failures.
 
- Load sharing between parallel running ropes Parallel ropes system require the equalization of the load sharing during the dynamic and static stages of the hoisting operation. The identification of bad equalization may be conducted by several methods and survey on the machine.
 
- Groove design. Grooves material and shape have an important rule with regard to the rope service life.
 
Sheave arrangement and terminations. The arrangement of the reeving system and termination location will dictate the bending cycle, the straddle angle, the steward and other parameters which affect rope life.
- Coiling and drum design
 
- Maintenance procedures Sheaves bearing, grooves etc
 
- Installation of the rope
 
- Hoisting procedure and rigs
 
- Safety devices as rope slack detector, load mesuring device, overload device etc.. 
- Discarding criteria and practice 
 
 
 
 

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