December 2015 / January / February 2016 : MT detection media: Should we talk about their detection sensitivity or their ability to detect discontinuities?

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Written by Laurence
Wednesday, 25 November 2015 00:00

The penetrant systems (product families) are qualified after determining their sensitivity levels according to the ISO 3452-2 standard, when using the Type 1 reference blocks of the ISO 3452-3 standard.

They may also be qualified according to the SAE-AMS 2644 American specification.

It is, therefore possible to use the word “sensitivity” for the penetrant systems (product families).

As for the magnetic particle testing, the ISO 9934-2 standard, as well as the ASTM E1444 / E1444M – 12 standard, do not state any test method to characterize the sensitivity of detection media (also called “examination media”), and there is neither any kind of reference test panel, nor any reference detection medium that would allow for the evaluation of the sensitivity of the detection media and for ranking them by sensitivity levels, as is the case with PT materials.

For its part, the ASTM E1444/-12 E1444M - 12 does not state the sensitivity check, but the "system performance verification" to be performed at least once a day, and mentions a reference test block similar to the one described in the ISO 9934-2 as well as the flux shunting indicators of the cross- or shim-type, which are shown in the ISO 9934-1 standard.

As a general matter, in their inspection specifications sent their suppliers, the primes list the detection media they approve, according to their own criteria and depending on the parts to be inspected.

It is interesting to know that one of us for a long time used the ... Paris-metro tickets(1), which have a magnetic stripe on one side (just like credit cards). These tickets, although not standardized for magnetic particle inspection, allowed, with some experience, for ranking the detection media in their ability to detect discontinuities or to check their "wear" (for in-service products, or those submitted to the mechanical stability test, i.e. long-term test, also called endurance test), as stated in the ISO 9934-2 standard. This is the mechanical resistance to the detrimental effects of the circulating pumps or of the carrier liquid, also called “suspension vehicle” (hydrocarbons, or water + additives), leading, in particular, to a fluorescent background. For the non-fluorescent detection media, a thin layer of white contrast aid paint should be first applied on the ticket. Each ticket can be used only once. Of course, these tickets were not to be submitted to a magnetic field!!!

An American company found this concept interesting enough to manufacture "magnetic stripe cards"(1) similar to credit cards. It improved it, succeeding in making stripes of different "sensitivities," thus, again, allowing for the ranking of brand-new detection media, or for the checking the deterioration of a detection medium. The test is "semi-quantitative" because the number of detected indications, and those barely detected, may almost be counted. The degradation of the detection medium may be identified when the indications are blurred, or dotted.

In conclusion, we may write about the ability of the detection media to detect discontinuities, but, in no way, about their sensitivity of detection.

 

References

(1)Pierre CHEMIN and Patrick DUBOSC, MT Materials Checking - Tools to check MT materials performancee, DPCNewsletter N° 014, July 2009,

 

Normative references

ISO 3452-2:2013, Non-destructive testing -- Penetrant testing -- Part 2: Testing of penetrant materials, International Organization for Standardization, Geneva, Switzerland, 2013.

ISO 3452-3:2013, Non-destructive testing -- Penetrant testing -- Part 3: Reference test blocks, International Organization for Standardization, Geneva, Switzerland, 2013.

SAE-AMS 2644F, Inspection Material, Penetrant, Society of Automotive Engineers (SAE), 400 Commonwealth Drive, Warrendale, Pennsylvania 15096, USA, 2013.

ISO 9934-1:2015, Non-destructive testing -- Magnetic particle testing -- Part 1: General principles, International Organization for Standardization, Geneva, Switzerland, 2015.

ISO 9934-2:2015, Non-destructive testing -- Magnetic particle testing -- Part 2: Detection media, International Organization for Standardization, Geneva, Switzerland, 2015.

ASTM E1444/E1444M - 12 Standard Practice for Magnetic Particle Testing, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, 19428-2959, USA, 2012.

Last Updated ( Wednesday, 25 November 2015 00:04 )