Re: Automated UT inspection of steel mill work rolls : : : We currently use eddy current flaw detection techniques in our roll grinding shop. I am interested in enhancing the process by
: : : combining this with automated surface wave and through body UT inspection.
: : : Can the panel indicate the level of crack resolution I am likely to achieve and suggest the best type of phased array transducer
: : : for this purpose.
: : : The following URL will take you to our site if you are interested in knowing more about Dofasco http://www.dofasco.ca
: : I don't completely understand the problem. Well, it's a
: : fact, that EC testing in ferritic material is restricted.
: : I don't know, if there is a static magnetic field for
: : premagnetization used, to enhance the penetration of
: : EC. If not, the penetration is very poor, but it should
: : inprove, if cracks are open to the surface and I think,
: : this should be the normal case. Remote field eddy current
: : shouldn't work in the case of a solid roll.
: : But in all cases, the sizing of the defect depth with
: : EC is still a problem. Will you use UT for sizing the
: : defect depth? Do you want to use phased arrays for im-
: : proving the accuracy of sizing by using several angles
: : of incidence or is the reason the arbitrary orientation
: : of the cracks?
: : We have experience with both. For example, we tested a
: : PA-probe for lateral skewing to +- 45 degrees. In this
: : case, the angle of incidence should carefully be
: : selected, because by skewing the angle of incidence
: : will change.
: : If the question is the voluminous scanning of your rolls,
: : PA probes are an adequate tool for doing this. With
: : selected angles of incidence you can inspect the whole
: : volume of your rolls and you can visualize the results
: : with tomografic methods. The capture of flaws perpenticular
: : orientated to the surface will be enhanced by using
: : wave conversion methods.
: Weused an EC system on ferromagnetic materials and detected and evaluated quite precise
: (with precision comparable to twice the roughness of the surface - typical for EC - in our case
: bout 0.3 - 0.5 mm) simulated (sawed) surface cracks with depths up to 3 mm.
: How deep do You want to go with EC, especially for EC? For testing steel mill work rolls,
: the only purpose of using EC, IMHO, is the testing of the near-surface zone
: in a very sensitive way - cracks in this zone are the most dangerous - because
: traditional US testing approaches do not give good results in the near-surface
: zone (about what I know).
: Besides, as I do not know too much about automated US testing, tell please,
: what's a phased array? (Please don't laugh too loud.)
: Jurcovici Florin
One difficulty for EC inspection of ferromagnetic material is changing permeability
from one surface point to another, which could lead to misinterpretation of the
resulting signal. One other point is the accuracy of depth sizing, especially
for non voluminous cracks. You have experience with depth sizing of small notches
in ferromagnetic material. Is this experience transferable to steel material
A phased array probe consists of a number of small piezo elements. The width of
each element is so small (in the range of the half wavelength), that a very broad
sound beam results. The individuel elements will be excited separately. Also the
received signals from the individual array elements will be amplified separately.
By firing the array elements time delayed, the resulting sound field can be formed.
This means,that as well the beam angle as also the focus can be controlled
by electrical steering of the time delays. Normally the received individual
signals will also be delayed in the same way, before summarizing to the resulting
Most of the phased arrays are linear arrangements of 8 to 32 elements. In the
future, with decreasing size and price of electronics, 2-D-arrays should become
Examples for linear phased arrays you will find in the "Ultrasonic Testing
Encyclopedia" under URL http://www.ultrasonic.de/article/ut_az/ut_p/ut_p.htm or in the
NDT-exhibition under URL http://www.NDT.net/exhibit/cust_sh/sie_sh1.htm.