FIELD OF APPLICATION
The present invention generally relates to a method for evakiating the toimlness
of rails using ultrasonic tasting. In particular it is related to an impravad nort-
dastructive uhrasonlc testing tachniqua, to evaluate the soundness of rails by
assessing the surface as well as internal (sub-surface and deep seated) flaws /
cracks aixi its siias, particularly at the comers of the raHs.
BACKGROUND OF THE INVENTION
Evaluation of the soundness of rails by assessing the surface as waN as the
iNamal flaws and cracks is aMkal for their life as these ffanvs and o'acks may
ultimately lead to avokJat»le acckients.
There is no ofT-lina non-dasiructive tasting technkjua which couU accurately
evakwte the soundness of the raUs by assessing tight shaifow surfKe breaking
cracks (surface flaws of depth less than 1.0 mm) on the surface, particularly at
the corners of the raUs flaws as weU as internal (sUb-surfaca and deap'saated)
flaws and their sizes.
The cracks are originated either due to manufaduring fault of the raHs or due to
reskkial, thermal mnA machank^al siFassas davatopad during their service. Alter
some time, if these aacks are missed by viwal inspection, they may propagate
further, during their service Hfo leading to foikire and causing fatel acckfants.
A known method of aamwsing cracks is by AC potential ffr^p iMthod, How«v«r,
V6rf tight surfice cracks, particutari)r at the comers of (he r^k, invielbte to
naked eyes cannot be assessed and measured for their depths, by using this
mtttiod:
Another known method is by using tjme of fHght cWfractton. However, the depth
of the shaibw surface cradcs (less than 1 mm) cannot lie anesMd and its de|Mh
measured wHh any accuracy by thw method.
A magnetk partk:ie testing or eddy cunrerA testing metltod used for assessing
flaws also has its disadvantages. The intemai (sub-surface as well as deep-
seated) flaws cannot be assessed and their sizes cannot be measured accuraleiy
by using such a metliod.
SUMMARY OF THE INVENTION
The main object of the present inventktn therefore, is to provide an oMIine non-
destructive t^asonic testing method for accur^Ma evariurtkin of the soundnem of
rails.
This and other objects are achieved in the present inventkNi by using sbighi
crystal creeping surfoce wave probe along with 35** and 45** angki probe and twin
crystal normal probe, for evakieUng the soundness of the raMs by aesessing tight
shaibw surface breaking cracks (surfaM flMvs of depth less than 1.0 mm) on the
surface, partkularly at the comers of the rails flaws as well as intemai (sub-
surface and deep-seated) flaws and their sizes, within the accuracy of ± 5%.
This method is insensitive to the wnMi of the crad(s since the uttrasonic pulses
are reflected from one wall of the aack only.
Tht tr«wv«rM and ioni^udirail w«¥ts of ultrasound travti through th« materiai
whtr&m surhn wave of uttracound travtf akng tha furfSaea of a malariat at a
daplh of 1 (one) wavelenglh from the surface. WItile traveMng, when it interacts
a flaw, (having depth leas than one wwftlani^ In cast of surface wave) they art
reflected iMck to create an ultrasonic signal on the oscllloccope. The amplitude
of the reflected signal is a (iaiction of area of the reflector (normal plena of the
flaw).
A direct correlation tMtween flaw location and its size and the amplitude of
reflected signal has t)een observed during experimentation with holes and
rwtches made on ciriibriAion l>locks of rmrterials similar to rail mafterial.
It has been observed that ttwJvnpMude of the reflected signel in term of its
location on oeeiNeacope am(3)liiN screen hei(^ is directly proportionel to the
flaw loc^ion and size. Therefore, using this reletion, it is pos«l>le to assess the
flaw iocirtion and their sizes.
After implementation on the rail sample, it has been obeerved that using this
technique, it is posstrfe to evakute the soundneM of die raNs by assessing the
flaws and their sizes within an accuracy of ± 5%.
The present invention overcomes the drewbaeks in the prior art methods Mce AC
potential drop method, time of fUgl^ deflraction method and eddy current testing
method as described above, by using sint^ crystal creeping wave, single cryrtai
35** and 45^ angle probe and twin crystal normal probe measuring the ampktude
of the reflected ultrasonic echo in terms of Its position on oscilloscope an^ %^i
saeen height from a flaw, it is possible to predict the loa^ion aiKi «ze of the
flaws wftf>jn accuracy of ± 5%. For this, callyation blodcs, made of rail material,
were prepared. Such caltfyatkm blodcs used to assess the surface, sub-surface
and deep-seated flaws and their sizes in the rails. There was a good agreement
between ultrasonicaHy and acturily measured flaw size in these rails.
ThiK the present inveirtion provides a method for evalurting the soundness of
rails using iritrasonic testing, con^irising: providing a plurality of uttrasonic
probes and positioning said probes on head, web and foot portions of the rails
under test; and measuring the ampfitude of reflected ultrasonic echo; thereby
predicting location and size of a flaw.
BRIEF DESCRIPnON OF THE ACCOMPANYING DRAWINGS
The invention wili now be descrfeed using the figures of the accompanying
drawsit;^ where:
Figisre 1 shows a «^matjc diagram of a calliration block.
Figure 2 shows a schematic diagram of notched calMsration
blodc made from a r«l sample.
Figures 3 shows position of i4lrasonic transducers and ultrasonic beam
directions in tiead' fxortion of rail sample.
Figure 4 shows position of uttrasonk transducers arxi ultrasonic beam
directions in *web' portion of rail sample.
Figure 5 dwws position of i^asonk transducers and ultrMonk beam
directions in *fiDof portion of rail sample.
DETAILED DESCRIPTION
As shown in Fig. 1 a callKation block made of rail sample showing 1.5 mm dia.
drilled hole 1 in head, and 2.0 mm dia. drilled holes 2, 3 in web and foot
respectively is fabricated to caKbrate an uttrasonic flaw detector equipment for
evakiatirtg the soundness of the raUs.
Figure 2 shows a notched calibration block made from rail sample fabricated
to caHbrate the detector equipmer^ for evakiating the soundness of
rails. 1.5 mm ncrtdies of deptti d are made as shown In Figure 2. Table 1 dwws
the notch numbers and their depth d in mm In the c^ibration blocks.
Rgur«s 3 to 5 show in scKtriMrtk dwgrafn form th« position of uHrMonic
probes and uMrasoroc b«am