ASNT Fall Conference Seattle '96
Report by Rolf Diederichs
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It was a full program, so it was not possible to attend all presentations of interest - there were just too many parallel sessions, as you will see here in the program - more than 100 lectures of the Professional Program in addition to a lot of other Meetings and Events. Nevertheless, we tried to pick up as much as possible and we hope you will excuse the omission of those good contributions we could not cover.
Qualification and Certification of Nondestructive Testing Personnel
That issue was discussed a lot. It's been discussed for years now, hasn't it? The main issue here is that a standard that would be recognized throughout the US has not yet been achieved. Still, companies suffer for lack of standards when they try to get an order for service. Personnel must be retrained every time they change jobs. When preparing to perform NDT, we are often required to use standards, reference blocks, or calibration blocks to set up a test system. We do this so that there is consistency, traceability, and repeatability. Why do we require our test systems to be calibrated to specific standards and not the personnel performing the examinations? We think that too much competition among some major NDT associations/companies may be an impediment to achieving this very reasonable goal. While we are still debating this, a new issue appears on the horizon - the International issue. What about EFTA, EU, etc, or the Global Market which is so important today? Some will say "lets solve our national problem first; international considerations are even more difficult." We should really tackle the global issue before throwing together a national solution that could soon become more or less worthless. For that reason, Mr. Schnitger, Mr. Link, Mr. Kaps from the German NDT society were at the conference, meeting with the ASNT to discuss harmonization, while it was clearly stated that the EU standard EN473 has to be maintained.
Tobey Cordel focused on this issue in his keynote as an important need. That's why this writer, a member of the NDT society, attended the Publications activities division held at 14th of Oct 9am. First, some typical business topics such as "high inventory" were discussed. Second, there was a demand for ASNT publications to be more widely recognized, and a call for efficient marketing. That was the moment when Rolf Diederichs introduced his ideas for assistance of ASNT through his publication, offering to publish typical things like book reviews on UT-Online. He also offered a place on the UT'96 CD-ROM for ASNT's Homepage material, free of charge, pointing out that this could be a great resource for NDT readers. Unfortunately, these good ideas were refused. Competition again? We already mentioned competition as a factor in the issue of Certification of Personnel. It is interesting to note that many ASNT members are open minded on the subject; Tobey Cordel emphasized the need for it.
Let us leave this unpleasant political scene and go to some nice UT applications.
Ultrasonic Committee Meeting
The chairmen Dr. Yoseph Bar-Cohen opened the meeting. However, but first we learned a little bit about the American way of life as we ate out box lunches :-) Picture. That way, the morning session could end at Noon and the afternoon session could start at Noon. Changes in the ASNT Training Manual UT Level I, II, III.It were introduced and discussed. The text was changed and added to according to today's state of the art. Here are some examples of items added to the recommended training curriculum for Level I: Other types of transducers (Laser UT, EMAT, etc.), Air coupling, Plate waves. Level III: All changes for Level I and for Pulse generation were added, specifically spike, square-wave, and toneburst pulsers.
A Bias Assessment for In-Situ
Ultrasonic Hardness Testing of Steel
Fasteners: M. Ratiu and
N. Moisidis, CALCET.
The problem of sub-standard and/or mismarked installed fasteners has received broad attention in quality control standards and has been largely discussed in technical publications and the public press. The purpose of this paper was to point out the specific consistent/systematic differences between ultrasonic intention hardness (HU) [Ultrasonic Testing Encyclopedia - Hardness testing] and the reference standard HR, which defines the ruggedness and bias of the ultrasonic method. The paper showed results of HU for in-situ inspection of mounted bolts which can be efficiently introduced for the quality validation of fasteners without reliable marking and/or test certification, only if the method bias and the test condition are established and included in the procedure. Without a pertinent investigation of the test ruggedness and the specific bias, the ultrasonic test results are subjected to large errors, and are therefore inconclusive for the inspected fastener quality. (Remark: The writer is proud to introduce this application, for which he developed the first equipment (DHV 10) in 1978 when he started his career in Krautkraemer).
A Computerized Imaging System for
Ultrasonic Inspection of Steel Bridge
Components: I. Komsky and J.
Achenbach, Northwestern University
Imaging of the defects is becoming more and more preferred by operators to visualize the results of ultrasonic inspection. Using comprehensive ultrasonic images of the inspected areas bridge managers and engineers can make accurate decisions on steps needed to correct a problem. An imaging technique requires an adequate level of equipment for data acquisition, presentation and representation. However, the system must be suitable for use at bridge sites. Application of an inspection procedure based on a combination of different modalities of ultrasonic imaging was proposed in this paper. Igor Komsky pointed out that the time of flight (TOF) data is valuable information for 3-D imaging techniques. The system has been tested on specimens with artificial flaws and implanted fatigue cracks. Work is in progress to develop a portable imaging unit for full-scale field tests at bridge sites.
Mr. Erhard from the BAM Berlin visited the lecture and after the presentation, we asked him for his opinion. He said "What impressed me here is, that with relatively simple equipment, consisting of an inexpensive transducer array, a presentation of good imaging results was achieved".
Pulse Echo Ultrasonic Inspection of
Thin Coatings: C. C, Wright
Patterson AFB; J. Wagner, The Johns
Fiedler informed us that the Air Force uses a wide variety of thin coatings because of their unique mechanical, optical, electrical properties. A technique was developed using ultrafast pulse of laser light to generate high frequency ultrasound, and to detect ultrasonic echoes. A completely non-contact method, low energy laser pulse does not damage the coating, making this technique nondestructive. The thickness of coatings as thin as 30µm, and as thick as 400µm was measured. For echo detection, an innovative delay line based pulsed interferometer was used. A frequency analysis of these echoes showed they contained significant energy as high as 100 GHz. Actually the principle uses the measure of the reflectivity of the surface, hence there is a function of interaction with the surface. Fiedler pointed out that the coating material must be piezoreflective, for other cases the lab is proceeding with the development of a modified interferometer.
Corrosion Detection in Aircraft
Structures using Guided Lamb
Here is the full MS Powerpoint Presentation
A. Chahbaz, V. Mustafa and D. Hay, Tektrend International (Canada). (Homepage).
This was a presentation which explained the propagation and advantages of Lamb waves for inspection of aircraft structures. This work demonstrated the benefits of Lamb waves for detecting and locating corrosion in aluminium metallic structures. The guiding character enables them to follow curvature and reach hidden parts. Results on real Labsplice joints from Boeing 727 aircraft were obtained and will be reported in a future paper.
Guided Wave Applications of
P. Meyer, Krautkramer Branson; J. Rose, Pennsylvania State University
This was another presentation of Lamb waves. We all know the results we can get for defect testing, thickness measurement and material characterization using the ultrasonic pulse echo method. Paul Meyer suggested in this presentation that for certain geometries a guided wave (Lamb Wave) approach maybe much faster in getting results. By use of conventional UT technique a part needs to be scanned to get a test result for the entire area. Plate waves or lamb waves had already been introduced in textbooks by the year 1940. While there have been improvements in the area of composite transducer use, there are a lot of advantages for to technique. The advantage of guided waves is that they can integrate plates or tubes initially from just a simple location so you can get the information of the target structure back perhaps much more quickly than you could with a mechanical scan. They are mostly applied to rods, tubes, layers and embedded layers. Paul Meyer introduced the complex action of lamb waves. The types of mode that exist depend on the frequency of incoming waves, the plate thickness and the angle of incidence. By changing the frequency the type of mode can be controlled. The selection of the appropriate mode is very important to inspection optimization. The advantage is now that broad bandwidth transducers can permit the generation of more modes and improve probability of detection, classification and sizing. We also have to select the appropriate mode to get the best sensitivity to your particular type of defect. The limitations are that lamb waves are not practical for material thicker than 0.25 inch and a basic understanding of flaw geometry is required. Graphs of lamb wave applications of piezocomposite transducers were shown, such as inspection of: Lape splice joint inspection, tear strap inspection, steam generator tubing, analysis of thickness degradation, and powder metal part characterization during manufacturing. Summary: Lamb wave techniques may be faster and more effective for ultrasonic inspection of certain geometries. Piezocomposite transducer technology enhances these methods. Experimental results demonstrate the usefulness of the technique.
Improved Sound Field Penetration using Piezocomposite Transducers: P. Meyer, Krautkramer Branson. This was incorporated into the above review.
A New Generation of Ultrasonic
Systems for Dimensional
Measurement of Tubing
R. Shannon, Westinghouse STC; L. Moga, Westinghouse SMP; J. Cuffe and S. Herbster, Krautkramer Branson
It was interesting listening to a lecture in Seattle about an application which the writer had already applied years ago in the plastics market. Read about Principles of Dimensional Measurement of Tubing OD/ID . Of course Mr. Shannon introduced today's advantages such as high accuracy, achieved by new fast digital signal processing (DSP) techniques (200 MHz) as well as use of the zerocrossing method for the TOF measurement. Also, the system works very fast with PRF of 10 KHz for each channel - essential for use in the production process. The design watches carefully for compensation of temperature influences, which can be caused by water. (Remark: Later, we discussed an error that can occur due to length changes in the probe fixture). One attendee asked if the system could be used for coated tubes as well, and give an additional result of the coating thickness. In principle this has been already tried successfully for plastic gasoline tubes. However, there were doubts about whether the system software would need a lot of changes.
Rapid Inspection of Aerospace
Structures - Is it Autonomous Yet?
Y. Bar-Cohen, JPL/California Institute of Technology
Multifunction Automated Crawling System (MACS) - Homepage
An Introduction to the recent NDT scene at NASA. Aircraft is getting older and this increases the demand for NDT. This is also true of the NASA Space Shuttle. In addition, we have to watch for new materials that will bring new requirements for NDT. Conventional techniques have the problem of human error. Hopefully, today with computers we can find ways of minimizing this. Telecommunications will also change things a lot; those techniques could be incorporated into our scanning systems. There is also increased demand for rapid NDE of large and complex-shaped aircraft structures, that can operate in harsh, hostile and remote conditions (extreme temperatures, battlefield, remote operation, etc.), with minimum human interference. Why not carry out such inspection remotely on the Balkan peninsula? (Yosi's light pen was out of order, he joked "this device we should do also in remote"). Furthermore he mentioned applications with new flat portable bridges (made by QMI or Tektrend) and reviewed the development of the MAUS from McDonnell Douglas Aerospace. However there are limitations of stationary portable c-scan bridges. Multifunction automated crawling system (MACS). In recognition of a small, more maneuverable crawler, JPL recently developed a small, highly Crawling system (MACS) was designed to perform robotic tasks in the inspection of aircraft external surfaces . MACS employs ultrasonic motors for mobility and suction for surface adherence. The development of the MACS crawler is benefiting from leveraging of the ongoing NASA miniatured planetary rover, telerobotics and NDE technology (see picture). Autonomous crawler - The future of portable rapid scanners. Such devices can be operated during an aircraft's idle time reducing the need to ground aircraft for inspection. A combination of visual, ET and UT payload are expected to be the leading NDE tools that will serve as the payload of an autonomous crawler. Miniature robotics technologies with on-board intelligence are needed for rovers to collect samples from Mars. Since communication lag between Earth and Mars is about 40 minutes, the need for autonomous operation on Mars has become a critical technology challenge.
During the discussion someone expressed doubt that high cost could justify practical use. Yosi answered that of course mass production will achieve a reasonable price.
Remark: Is is interesting how incoming news matches this subject. The FhG Institute reported: "3-D Ultrasonic Pictures in Medicine were obtained under battlefield conditions in Bosnia during the NATO occupation. When diagnostic images were made with this portable equipment, new telecommunication techniques made it possible to do remotely, getting support and assistance from experts all over the world. Of course, the 3-D issue here also addresses an important subject" (Press release contact: email@example.com)
Development of Two Advanced
Ultrasonic Inspection Systems with
G. Schenk, A. Erhard and T. Mauser, Institute for Material testing BAM (Germany) Berlin - NDT Department 8
The principle of Phased Arrays is based on the subdivision of an ultrasonic transducer into separated elements. The electronic control of the signals of these elements opens up various and splendid possibilities to manipulate the soundfield. This covers the variation of the angle of incidence, the focal depth and the displacement of the local position of the sound beam. All variations may be executed in real time by computer programs. This paper gave an introduction into instrumentation technique for Phased Arrays and the presentation of two systems designed recently at BAM. More information
Rolf Diederichs 01. Nov 1996, firstname.lastname@example.org