Ultrasonic Testing - Specification and Interpretation.pptx

Ultrasonic Testing

1. Ultrasonic Testing of Plates Plate Specifications and Interpretations

2. Contents : Basic 2) DAC and Plotting of DAC. 3) Major Plate Mill Specification and Interpretation. 4) Auto UT at a Glance.

3. Conventional / Manual UT in Plates Manual Ultrasonic Testing consists of a search Unit and Probe attached to it. In pulse-echo testing, a transducer sends out a pulse of energy and the same or a second transducer listens for reflected energy (an echo). Reflections occur due to the presence of discontinuities and the surfaces of the test article. The amount of reflected sound energy is displayed versus time, which provides the inspector information about the size and the location of features that reflect the sound. 2 4 6 8 10 initial pulse crack echo back surface echo Pulse Echo Method

4. Conventional / Manual UT Digital display showing signal generated from sound reflecting off back surface. Digital display showing the presence of a reflector midway through material, with lower amplitude back surface reflector. The result are interpreted by personnel qualified in Level II in Ultrasonic Testing.

5. What is a DAC ? Signals for same size defects at different depths produce different signal heights on the screen. Same size defects at far depths produce signals much lower than that from defects which are near to the surface ( Surface of the probe contact). To bring this in same level DAC is drawn. The Distance Amplitude Correction (DAC) provides a means of establishing a graphic ‘reference level sensitivity’ as a function of sweep distance on the A-scan display. 

6. How to Plot a DAC ? Reference Block – Reference block is made of same thickness and same material of the plate for which we have to do the testing . Make 5 mm Dia Flat Bottom Holes at Different Depths of the reference block

7. How to Plot a DAC ? 1 .)  Position the transducer over the 1/4T hole and peak the signal to approximately 80% FSH (Full screen height), mark the peak of the echo on the display using a suitable marker, and record the gain setting . 2) With no further adjustments to the gain control, position the transducer over the 3/4T hole and peak the signal, mark the peak of the echo on the display .

8. How to Plot a DAC ? Similarly again without changing the gain position the probe to T/2 Position and mark the point on the screen. To complete the DAC curve connect the dots with a smooth line.  The completed curve represents the ‘reference level sensitivity’ for this application. So this is a DAC corresponding to 5 mm Dia FBH. Any indication above this line represents a defect greater than 5 mm in dia and any defect below this line represents a defect less than 5 mm in dia.

9. Major Specifications Used at Plate Mill Reference - Back Wall Echo Specifications which are evaluated on reference of back wall echo. These are Used to Detect Bigger Defects . These Specs are applied where the requirement of plate has less stringent application. Most Importantly these can only be detected when the size of the defect is bigger than the size of the probe which we are using. In these specifications there is a single defect size above which if any single defect is also present will not be accepted. ---- ASTM 435. ---- ASTM 578 ( Level A ; Level B and Level C)

10. Major Specifications Used at Plate Mill Reference - An artificial Defect – FBH Specifications which are evaluated on reference of reference artificial defects ( Flat Bottom Hole – FBH ) . The most common FBH size that is used in plate inspection is 5 mm Dia FBH. These Specs are applied where the requirement of plate has high end application. These can be used to detect and evaluate the defects with size much smaller than the probe used. To use specifications a DAC ( or DGS for more advanced systems) has to plotted and defects has to evaluated on basis of this.

11. Exact Defect Sizing is possible in these specifications. Most Importantly when these specifications are used we can evaluate the defect size which is greater than the size of the artificial defect. These specifications have different acceptance criterion for Plate Body and Plate edges – Plate Edges being more stringent. In this there are two Defect Levels – Minimum and Maximum. ---- EN 10160 ( Body S0; S1; S2; and S3 ) and Edges ( E0 to E4).o ---- SEL 072 (Body Class 0 to Class 6) and Edges (Class 0 to Class 4) ---- IS0 12094 ( Body 3 Levels and Edges 3 Levels). ---- BS 5996 and more. Major Specifications Used at Plate Mill Reference - An artificial Defect – FBH

12. Evaluation Technique. For ASTM ( Where Backwall Refernce is Used) There must be 100 % Back wall loss and we have to check if that area is more or less than the standard requirement. ASTM 435 -- 75 mm ASTM 578 Level A and B -- 75 mm ASTM 578 Level C -- 25 mm. Evaluating ASTM is easier.

13. Where FBH is used: We will take the example of EN10160. The below is the acceptance Criterion for the Plate Body as per EN10160 Evaluation Technique.

14. Tips for Evalution : There are two defect size – a) Maximum Defect Size – Even a single defect above this is not acceptable. b) Minimum Defect Size -- All defects below these are acceptable The defects which are between these two sizes are accepted only for a Particular number of counts which is mentioned in the specification. 2) FBH size must always be smaller than the Minimum Defect size. 3) Always try to make the defect in circular size for comparision . Evaluation Technique.

15. Evaluation Technique. – Example EN10160 Body S0 Level. Maximum Defect Size : 5000 square meter. Let us consider is it is a circular defect --- This will Give the smallest Diameter of the defect. So π r 2 = 5000 square mm . ( Area of Circle Formulae) . Calculate r = 39.9 mm and so Dia = 79.80 mm. Minimum Defect Size -- 1000 mm. So Dia - 35.69 So Any defect above and equal to 79.80 mm anywhere in the plate is not acceptable. Any number of defects below 35.69 mm are acceptable. And 20 no of defects in size between 79.80 mm and 35.69 mm in one square meter area acceptable. So if there are more than 20 defects in size between 79.80 mm and 35.69 mm in one square meter area then it is not acceptable and it leads to rejection.

16. Evaluation Technique. – Work Out EN10160 Body S1 Level and Edge E0 and E1

17. What is a 6 dB Method -- Defect Sizing. With a DAC we can say if the defect is bigger or smaller than the DAC FBH size. Suppose if we draw a DAC of 5 mm Dia then if the defect echo is above the DAC line we can conclude that the defect is greater than 5 mm in size and vise versa. But we cannot predict the exact size of the defect. For this we have to use the 6dB Drop Method. -- Locate the position with the highest indication Height. -- Move the prove left till the defect height is half the original point. -- Move the prove right till the defect height is half the original point. -- Move top and bottom similar ways and mark the points. -- Join these points and that is the size of the defect.

18. Online Ultrasonic Testing Machine. Plate Mill has a Online Ultrasonic Testing Machine with the following features Make : NDT Systems and Services-Germany; Type - HP - B2/L2-TR3. Full body coverage with 2% Overlap to ensure that there is no untested area. Consist of 100 probes of 5MHz. Each probe having one transmitter and three receivers. Scanning Speed is 1000 mm per second. Display of results in C scan and B scan showing the plate Top Surface; Thickness and width showing the position of the defect Automatic evolution of the plate data with the International specification. There are various international specification built in the machine which compares the plate data with the specification and gives the result as “ Pass “ or “ Fail”. Covers a width of 5000mm .

19. Online Ultrasonic Testing Machine. UT System consists of following core components : Two Carriages A and B, each equipped with 48 wide beam TR probes (total 96). One Longitudinal plate edge inspection system with two movable units , each equipped with 2 wide beam TR probes covering a track width of 100mm along the edge. These 100 independent TR probes comprise the necessary mechanical and pneumatic parts, coupling water supply, and peripheral sub systems for control, Ultrasonic electronics, Ultrasonic data preprocessing. Central systems for control, Ultrasonic electronics, Ultrasonic data preprocessing. Ultrasonic Data Evaluation Unit (DEU). This unit calculates defect area in comparison to FBH reference reflectors with a subsequent DGS Correction. A C- scan is presented on the operator screen representing the plate and graphically displaying the position of the defect and the sum of the defect areas for every test track. Results are displayed in the form of C – Scan.

20. CALIBRATION REFERENCE STANDARD: A Test plate with 5mm FBH at Depth of ¼ T;1/2T; 3/4T; 4mm from Top thickness and 4mm from bottom located at four corners and the body. Additionally slots of 5mm with depth at ¼ T;1/2T; 3/4T; 4mm from Top thickness and 4mm from bottom are located throughout the width of the plate. Additionally the Auto UT machine probes are also calibrated in self testing mode with the 20mm Test block attached to the machine body.

21. EVALUATION AND ACCEPTANCE CRITERIA The inspection, data acquisition, defect data processing and evaluation is mainly carried out with low operator interaction. Flaw size determination is through DGS Method. The data of the plate is automatically compared with the reference specification and the result is declared by the Machine as pass or fail. The defective part of the plate is encompassed by a Red area and depicted on the C Scan on the display .The plates that are failing in AUT are re verified manually full plate and the result is declared. The Plates that are failed in UT are marked with yellow paint at the side and are deallocated from the order in the system

22. ULTRASONIC TESTING LEVELS INBUILT IN AUTO UT MACHINE ASTM A435 GB 2970 ASTM A578 ISO 12094 EN10160 JB 4730 SEL 072 JIS G 801 BS 5996 JIS G 901 EN0246 NF A04-305

23. ONLINE UT MACHINE SCAN REPORT.

24. Thank you