Abstract

The safe using of different kinds of the lifting machines like cranes, mine hoists, air rope ways, lifts etc. depends on the steel wire ropes durability. The ropes are non repairable components of the machines.

There are regulations and standards, national and international, which fix requirements for the ropes (1-3).

Rejection criteria for the ropes are defined by the regulations (2,3):

• character and number of wires broken;
• strand breakes;
• friction wear;
• corrosion;
• decrease of a rope diameter,
• deformation.

All the above mentioned defects result in the durability loss. So, ropes having defects must be changed. Besides, ropes being in use have living time limitation. A work fulfilled by a rope and performed in tone-kilometers may be used as a limit too (1).The most of regulations in force establishes a visual method as base one for wire inspection. Instrumental methods using rope flaw detectors are considered as additional ones. But the visual methods have number of shortcomings:

• are imposs ' ible to detect the cross section area loss caused by inner wiresfriction and corrosion as like as inner wires broken;
• take long time work of an operator skilled;
• often are dangerous for the operator,
• do not left documents of objective result recording.

Evaluation data taken from the more than 8 thousand protocols of laboratory and field wire ropes inspections show that the visual methods and life time criteria are non adequate to real durability of the ropes in service (1).

Approximately 10% of all ropes considered showed a strength loss of over 15%; more than 2% of the ropes had lost over 30% of their nominal strength. That means, while still in service, 10% of all ropes were in an unacceptable and potentially hazardous condition, and 2% of the ropes were extremely dangerous!Conversely, more than 70% of all ropes in the sample were removed from service with little or no strength loss.So, only a very small percentage of all ropes was replaced in a proper time, when one has used a visual inspection.Electromagnetic NDT instruments allow to increase the test records reliability. They are most efficient for detection of the rope durability loss as a result of: - loss of metallic cross-sectional area (LMA) - localized faults (LP) like broken wires, localized corrosion etc.

Keywords: Magnetic Testing

Source: Conference Proceedings of the 4th International Conference of the Slovenian Society for Nondestructive Testing, 24 - 25 April 1997, Ljubljana, Slovenia.
Pages:229 - 238

Publisher:
Slovenian Society for Nondestructive Testing, Faculty of Mechanical Engineering, Askerceva 6, SLO 1000 Ljubljana, Slovenia. Tel +386 61 177 12 03, Fax +386 61 218 567, Email: janez.grum@fs.uni-lj.si.