Electromagnetic NTD state of the art - background and prospects
Current concepts of electromagnetic nondestructive testing (NTD) along a rope length have been discussed. The following factors contributing to the problem have been considered:
- NTD procedures in relation to touch-and-see methods;
- NTD devices and their duty specifications;
- decision making from NOT findings and justified limiting conditions;
- evaluation of NTD duty specifications and approval procedure of NTD
devices for industrial use; and,
- NTD personnel requirements.
Discrepancies between the contributing factors give rise to different retirement approaches and criteria, which, in turn, result from ambiguous definitions of wire rope limiting conditions. The reasons behind this situation are:
- lack of a precise definition for residual strength of a degraded rope;
- degradation varieties due to various operation conditions; and,
- complex effect of wire break increase on decision making.
Quite another problem consists in determination of the number of wire breaks, their localization and analysis of the wire break increase. This problem leads to a judgement on rope replacement based on deterioration rate. Research findings gained by MakN II in the course of tensile tests on degraded ropes demonstrate a significant stochastic relationship between residual strength, affected by all types of damage, and an integral criterion, i.e. the loss of metallic area measured by NTD. This implies some very specific conclusions as to the problems influenced by the factors mentioned
Author(s): Berezhinski, V.