DIAGNOSIS OF AGEING IN FATIGUE OF THE EQUIPMENT


With the difference of the majority of the other phenomena of materials rupture, fatigue is a cumulative phenomenon whose origin is heterogeneity on the intimate level of the matter, the extent of the phenomenon is random, the results of the tests present a great dispersion and calculations of lifespan thus use statistical methods.fallen bridge

The description of an office plurality of damage by fatigue is impossible by non-destructive testings because the guiding principle of the checking in fatigue is “to guarantee, within the framework of the probability of the method that during the lifespan no fissure of size higher than critical dimension (detectable by non-destructive testing) will appear”.

In the general case and more still in that of the welded joints, it is almost impossible to know in a realistic way the speed of a fatigue crack evolution.

The application of the step was extended to the port activity for the following reasons:
- the port activity is a hazardous activity and the number of serious accidents and incidents which could occur, whose origin is the development of fatigue cracks, is important and even seems to increase in gravity.

- The correspondent penal risk is felt with sharpness by people in charge of harbors.

The standard ISO 12482-1 deals with condition monitoring of cranes. Its Purpose is to ensure that the design constraints of the intended use of a crane are clearly identified and to define actions to be taken when the crane has been used over a period of time and has approached these constraints, to ensure a new safe working period. A description is given of the special assessment required to monitor the condition of a crane.

This standard is almost mandatory in the French harbor.

- ageing in fatigue it affecting in an unequal way the various elements and their assemblies, a comprehensive approach on the scale of the machine compared to its contractual classifications is not sufficiently relevant taking into consideration risk (different stresses, different services, quality of execution, controls carried out during the execution…).

The sensitivity of the variation of the various parameters influencing over the lifespan of the assemblies being often important and sometimes considerable, it is essential that, for the diagnosis of ageing in fatigue of the machine structure, the last services (histogram of the loads in number of cycles) are reconstituted with more great care and in the most realistic possible way and that the estimate of the concentration factor of stresses is a very pragmatic step.

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By this procedure AQUASS :

- In the framework of the policy of their equipment optimization, AQUASS answers the interrogations that are asked by the owner of lifting equipment.

  1. Assessment for decision of activity extension or downgrading.
  2. Modernization policy (with or without increase in the performances)
  3. Policy adjustments concerning preventive controls of fatigue

schema- Bring a solution to the problem raised by the non-destructive testing while not making it possible to determine one residual lifespan before possible ruin

- Applies a pragmatic method deposited which leads to directly exploitable information for the overall management of the equipment.

- Goes beyond the harbor histories and statistics which are not carried out in the objective of an activity reconstitution of the equipment under the angle of fatigue

- Allows to establish a prevention policy of the risks regarding the environment.

This study of ageing also known as special evaluation allows to determine the residual lifespan of a lifting device (or any other mechanical structure complexes motorized) and to define a plan of monitoring and/or work for safety.


 

 

The method applied is the synthesis of the work completed in partnership with the French ports and the CETMEF between 2001 and 2003, to adapt the modes of enforcement of the standard ISO 12482-1 to the park of harbor hoisting and French handling equipment. This method is based on the “recommendations of the CETMEF” which was published in November 2003 in the form of the technical guide n° PM 03.01.

download the recommandations (french version only)

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Why carry out a study of ageing on your equipment?

  • The equipment structure is old (more than 10 years for certain equipment and 20 years for others according to their FEM category or other calculation code).
  • The number of operating cycles exceeds the number of cycles envisaged by the manufacturer.
  • The use expected in the beginning was modified.
  • The frequency and the importance of the dysfunctions is increasing.
  • The lifting device is an essential component with the production.
  • The equipment handles dangerous loads, and/or with strong added value.
  • The equipment moves in a sensitive environment.
  • To justify or plan the investment on new equipment

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Sequences of the study of ageing

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The study is systematically divided into four successive phases. The preceding phase determines the shape of the following phase, and each phase can stop the process if its results are too negative for equipment.

This special evaluation goes beyond the usual inspection during which only the state of conservation is estimated. The usual inspections are carried out at a one moment, and based on the observation of what exists. The special evaluation locates the zones where the probability of crack is highest.

 

In conclusion, the special evaluation is a method to protect you of equipment breakdowns and trading loss, by controlling the risks related on the fatigue phenomena and the ageing of their metal structure and their mechanical kinematic chains.

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