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IRIS -Testing with 3D-Presentation of Testing ResultsAarne Lipponen
Technical Research Center of Finland
IRIS-testing (Internal Rotating Inspection System) is used for flaw detection and wall thickness measurement of ferrite tubing in heat exchangers. The variation of permeability in ferrite material causes disturbing signals when using eddy current or other electrical testing methods. Because of the disturbing signals the accuracy of those methods is not sufficient for evaluation of the flaw size or flaw characteristics, not even to detect them all.
|Fig 1: Screen display of calibration tube containing OD flaws. The type of flaws (shapes) can be evaluated easily and the location of flaws can be measured and reported accurately.|
IRIS testing is based on ultrasound and is not impacted for electric properties of material. Only the material characteristics, which affect for ultrasound, should be taken in consideration. Those are e.g. the cleaning of tubing. There should not be any deposition or other dirties inside the tubing which could absorb the ultrasound and avoid the ultrasound to reach the front and back wall of the tubing material.
Using the IRIS-testing the absolute remaining wall thickness will be measured around the tube circumference. Each rotation of the mirror of the IRIS-probe will cater the whole circumference of the tube wall. The wall thickness will be measured for the whole length of the tube when moving the IRIS-probe from the inlet to outlet of the tube. At the same time the whole circumference of the tube wall will be tested.
During the testing the data will be recorded and saved for further evaluation. A lot of information of the condition of the tubes tested will be catered. With IRIS- method the typical flaws of tubing can be detected accurately and the type of damages can be evaluated using the data recorded. The testing data includes valuable information about flaws e.g.:
After collection of the data of the heat exchanger tubing there is need to find out all the damaged areas, evaluate the type of damages and to know the remaining minimum wall thickness. Also it is important to locate accurately all different kind of flaws and to present all that with a suitable and most informative way for maintenance personnel. The tools for doing final conclusions of testing data are:
Fig 2: Flaw depth histograms of follow-up testings. The grade of inside corrosion has reached the limit when the renew of the heat exchanger tubing has to be made.
|Fig 3: 3D- presentation of IRIS testing results. The tube support plate vibration has occurred OD wall thinning. The most aggressive thinning is near the area where the steam inlet is located.|
|Fig 4: 3D- presentation of follow-up testing results. Only the changes of flaw depth and the grade of changes (color-coded) are presented to locate the positions of damage areas. The black colored tubes are plugged during the previous testings. The maintenance personnel can start to design new constructions to avoid the propagation of the damage in the future.|
During acquisition and evaluation of the data it is important to know the history of the heat exchanger tested. If the maximum capacity of the heat exchanger has been reached during the operation period or if there has been thermal or pressure transients during the use of the heat exchanger all those should be taken in consideration when estimating the testing results and when making the final conclusion based on the testing results. This requires close co-operation between maintenance and testing personnel.
When comparing follow-up testing results the development of damages can be evaluated and the decisions of repair or renewing of heat exchanger can be made in time. All that means saving in time and the repair can be planned in the most economical way.
To take advantage of all the information of testing results and the visualization of the results is most important for the service and maintenance personnel. The testing results should help the personnel for to make right conclusion about the condition of the heat exchanger and give them the information if the process and process control systems are working well.
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