AS ISO 15549 pdf download

AS ISO 15549 pdf download.Non-destructive testing — Eddy current testing — General principles
1  Scope
This document defines the general principles to be applied to non-destructive eddy current examination of products and materials in order to ensure defined and repeatable performance. It includes guidelines for the preparation of application documents which describe the specific requirements for the application of the eddy current method to a particular type of product.
4  General principles
The eddy current examination is based upon the induction of an alternating electric current in a conducting material. The quantity measured and analysed is related to the distribution of the induced currents and it is represented by a vector in the complex plane. The distribution of eddy currents in the depth of a material is governed by physical laws, the density of the currents decreasing drastically with the increasing depth. For a given frequency, this decrease is an exponential function of the depth. The following properties, alone or in combination, of the product to be tested influence the measured quantity: — the electrical conductivity of the material; — the magnetic permeability of the material; — the size and geometry of the product to be tested; — the geometrical relationship between the eddy current probe and the product to be tested.More detailed information is obtained when the measured quantity is displayed in the complex plane. The method can be applied using the following characteristics: — the method does not involve any physical contact with the product; — it does not need a coupling medium such as water; — high throughput speeds can be used.
7  Examination techniques
Examination can be static or dynamic, the latter requiring the relative movement between the probe and the product to be tested. Scanning of the product to be tested can be performed manually or by the use of mechanized equipment which precisely controls the scan path.Commonly used measurement modes are: a) Absolute measurement. The measurement of the deviation from a fixed reference point. The reference point is defined by a calibration procedure and can be generated by a reference voltage or coil. This technique can be used for sorting a product into classes based on physical properties (such as hardness), dimensions or chemical composition. It can also be used for the identification of continuous or gradually changing discontinuities. b) Comparative measurement. The subtraction of two measurements, one of which is taken as a reference. This technique is normally used to sort a product into classes. c) Differential measurement. The subtraction of two measurements made at a constant distance between the measurement locations and on the same scan path. This measurement technique reduces the background noise due to slow variations in the product to be tested. d) Double differential measurement. The subtraction of two differential measurements. This measurement technique provides high- pass filtering of a differential measurement independent of the relative speed between the probe and the product to be tested. e) Pseudo-differential measurements. The subtraction of two measurements made at a constant distance between the measurement locations.
8  Equipment
8.1  Examination system The examination employs an eddy current instrument, one or more probes and interconnecting cabling. This combination, together with any mechanical equipment and peripheral units for data storage, etc., forms the examination system. All essential parts of the system shall be defined in the relevant application document (see 13.2) or in a written procedure agreed at the time of enquiry and order. Factors to be considered include: — the type of material from which the product was manufactured and its metallurgical condition; — the shape, dimensions and surface condition of the product; — the purpose of the measurement, e.g. detection of cracks or determination of thickness; — the types of discontinuity to be revealed and their position and orientation; — the environmental conditions under which the examination is to be performed. 8.2  Eddy current instrument The choice of eddy current instrument depends on the purpose of the examination. Of particular importance are the adjustable parameters of the instrument, the range of such parameters and the type of signal representation.