ISO 9934-1:2016 download free.Non-destructive testing – Magnetic particle testing Part 1 eneral principles.
It is assumed that magnetic particle testing is perlbrmed by qualified and capable personnel. In order to provide this qualification, it is recommended to certify the personnel in accordance with ISO 9712 or equivalent.
S Safety and environment
International. regional, national and/or local regulations which include health, safety and environment may exist and may need to be taken into account.
Magnetic particle testing often creates high magnetic fields close to the object under test and the magnetizing equipment. Items sensitive to these fields should be excluded from such areas.
6 Testing procedure
When required at the time of enquiry and order, magnetic particle testing shall be performed in accordance with a written procedure.
The procedure can take the form of a brief technique sheet, containing a reference to this and other appropriate standards. The procedure should specify testing parameters in sufficient detail for the test to be repeatable.
All testing shall he performed in accordance with an approsed written procedure or the relevant product standard shall be referenced
7 Surface preparation
Areas to be tested shall be free from dirt, scale, loose rust, weld spatter. grease. oil, and any other foreign materials that can afkct the test sensitivity.
The surface quality requirements are dependent upon the size and orientation of the discontinuity to be detected. The surface shall be prepared so that relevant indications can be clearly distinguished froni false indications.
Non-ferromagnetic coatings up to approximately 50 pm thickness, such as unbroken adherent paint layers, do not normally impair detection sensitivity. Thicker coatings reduce sensitivity. Under these conditions, the sensitivity shall be verified.
There shall he a sufficient visual contrast between the indications and the test surface. For the non- fluorescent technique, it might be necessary to apply a uniform, thin, temporarily adherent layer of approved contrast aid paint.
8 Magnetization
N.I General requirements
The minimum magnetic Ilux density B1 regarded as adequate lhr testing is I T. The applied magnetic field (II) required to achieve this in low-alloy and low-carbon steels is determined by the relative permeability of the material. This varies according to the material, the temperatures, and also with the applied magnetic field and for these reasons, it is not possible to provide a definitive requirement for the applied magnetic field. However, typically a tangential field of’ approximately 2 kA/m will be required.
Where time varying currents (1) are used to produce a magnetic field (which will also be time varying), it is important to control the crest factor (shape of the waveform and the method of measurement of the current in order to establish a repeatable technique. Both peak and RMS measurements are
typically used and measurement of the values can be affected by the response of thc instrement. For this reason. only insuumcnts thai respond directly to the waveform shall be used (e.g. true RMS meters with appropnate crest Iacioi’ capability for accurate RMS measurements). Instruments that calculate peak or RMS values based on theoretical calculation derived from ather values shall not he used. This shall also apply to instruments used to measure magnetic fields
Smooth shaped waveforms provide low crest factors and least variation between peak and true RMS values and arc regarded as preferable for magnetic particle testing. Waveforms with a crest lactnr(i.e. tRM%l greater than 3 shall not bc used without documented evidence of the effectiveness of the technique.
When using muftidircctional magnetization techniques. the current used shall be purely sinusoidal or phase controlled but the phase cutting shall not be more than 9(Y. Practical demonstration that the technique is effective in all directions shall be carried out (e.g. using sample part.s with known defects or shim type indicalon)
Provided the permeability is in the normal range and the current measurement methods arc controlled as described. calculations based on the use of 2 kAJm can provide a valuable method of technique preparation. The use of either peak current or true RMS current is acceptable if the crest factor is known. Knowing the entire waveform of the magnetizing curve would he optimal, but knowing the crest factor is a good practical approximation. For pure sinusoidal waveforms, the relationship between peak, mean, and RMS is shown in Annex A. Techniques based on calculation shall be vcril’ied before iinpleinentatkm.
NOTE I For steels, with low relative permeability, a higher tangential field strength might be necessary. Ii magnetization is too high, spurious background indications can appear. which could mask relevant indications.
licracksor other lineardiscsmtinuities are likely to be aligned in a paniculardirection. the magnetic flux shall be aligned perpendicular to this direction where possible.
NOTE 2 The flux can he regarded as effective in detecting discontinuitics aligned up to 60’ from the optimum direction. Full coverage can then he achieved by magnetizing the surface in two perpendicular directions.
Magnetic particle testing should be regarded as a surface NOT method; however. discontinuities close to the surface can also be detected. For lime varying waveforms, the depth of magnetization (skin depth) will depend on the frequency of the current waveform. Magnetic leakage lields produced by imperfections below the surface wifl fall rapidly with distance. Therefore, although magnetic particle testing is not recommended for the detection of imperfections other than on the surface, it can be noted that the use of smooth DC or rectified waveforms can improve detection of imperfections just below the swi’acc.
112 VerIfication .1 magnetizatIon
The adequacy of the surface flux density shall be established by one or more of the following mct liods:
a) by testing a representative component containing fuse natural or artificial disconlinuitics in the least Iavourabk locations:
hI by measuring the tangential field strength as close as possible to the surface (information on this is given in
ISO 9934-3);
C) by calculating the tangential field strength fur current how methods — simple calculations arc possible in many cases, and they form the basis for current values specified in Annex A:
d) by the use of other methods based on established principles.
Flux indicators (e.g. shim lype). placed in contact with tli surface under test, provide a guide to the magnitude and direction of the tangential field strength, but should not be used to verify that the tangential field strength is acceptable.
9 I)etccllon media
9.1 Properties and selection ad’ media
The characterizatioa of detection media shall be in accordance with ISO 9934-2.
Various types of detection media exist in magnetic particle testing. Usually the detection media isa suspension of coloured (including Hack) or fluorescent magnetic particles in a carrier fluid Water- based carriers shall contain welling agents and usually a corrosion inhibitor.
Dry powders are also available. They are generally less able to reveal fine surface discontinuitics. fluorescent detection media usually gives the highest sensitivity provided there is an appropriate sw’face finish. good drainage to masimize indication contrast, and well controlled viewing conditions, in accordance with
c11Q.
Coloured detection media can also offer high sensitivity if the contrast with the part surface is sufficiein. Black and other colours are available.
NOTE To achieve gtssl coltui contrast between discontinuitics and the lest surface. ii might he necessary to apply a thin b>cr of contrast aid paint in accordance with Cbuvcs land 10.
9.2 TestIng of detection media
ISo 9934-2 defines mandatory and recommended tests that are to he carried out before or pcnodically during inspection.
A sensitivity check shall be carried out before and periodically during testing, in accordance with ISO 9934-2 using a suitable reference piece.
If a magnetic ink is re-used or re-circulated, particular care shall be taken to maintain its performance.
9.3 Application or detection media
For the continuous technique. the detecting media shall be applied immediately prior to and during the magnetization The application skull cease before magnelitation is terminated. Sufficient time shall he allowed ftc indications to develop before moving or esamining the component or structure under test.
Dry powder. when used, shall be applied in a manner that minimizes disturbance of the indications. During application of a magnetic ink, it shall be allowed to flow onto the surface with very little pressure so that the magnetic particles are allowed to form an indication without being washed ofi
After applying a suspension, the component shall be allowed to drain so as to improve the contrast of any indications.
10 Viewing conditions
The viewing conditions shall meet the requirements of ISO 3059.
There shall be good contrast between the detection media and the lest surface, Where viewing is obstructed, the component or equipment shall be moved to permit adeqwale viewing of all areas. Care shall be taken to ensure that indications are not disoutbed after magnetization has slopped and before the component has been inspected and indications recorded.
11 Overall performance test
Before testing begins, an overall performance test shall be carried out to reveal discrepancies in either the procedure or the magnetization technique or the detection media.