PSI - Issue 14

Sameerkant Behera et al. / Procedia Structural Integrity 14 (2019) 112–118 Sameerkant Behera, S. K. Sahoo, Lokesh Srivastava, A. S. Srinivasa Gopal / Structural Procedia 00 (2018) 000 -000

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To know the exact nature of discontinuity present, high dB zones are correlated with tangential X-ray radiography images. X ray radiography was carried out at high dB zone using 4MeV LINAC machine. SFD of four meters and exposure time in order of one to two minutes was chosen for the test. Figure 11 represents radiographic images of high dB loss zone and followings are the correlation established.  Zones observed more than 12dB loss has been found to be delamination or debond. (fig.11. (a), (b), (c))  Zones observed between 6dB to 12 dB loss are found to be of porosity or voids or resin lean area. (fig.11. (d))  Zones observed up to 6dB loss are found to be resin rich area. (fig.11. (e))

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Fig. 11. (a) Delamination at dome; (b) debond between main shell & composite skirt; (c) Outer ply delamination

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Fig. 11. (d) Resin rich area (6dB loss); (e) porosity (6-12dB loss) The zone showing more than 12dB up to total signal loss is mapped and quantified in terms of percentage area with respect to total scan area. The above high dB zone has been found to be less than 5% of the total inspected area and rest other zones cumulatively found more than 90% where more than 90% of full scale height has been observed. With this, the above pressure vessel is found to be fit for end use. Above criteria is derived based on the results obtained from various nos. hydraulic pressure testing, qualification testing, ground test and actual end application data. However same may not be applicable for other configurations. Otherwise high dB mapped area and its location can be used as an input to the designer and to carry out analysis to find out margin of safety based on which decision can be taken for acceptability. 6. Conclusion With the above, through transmission ultrasonic test procedure for detection of defects in large size composite pressure vessel is established and proven by implementing above procedure in successfully end used more than twenty no’s of full scale product. It is observed that ultrasonic response for delamination are found to be more than 12 dB loss. Same has been verified by correlating with X-ray radiography images. To know exact nature of discontinuity, it is always preferred to use alternate complimentary NDT technique such as tangential radiography technique. In order to assess structural integrity, high dB zones area to be mapped and quantified in terms of inspected scan area to find out whether it can be tolerable or else it can be used as an input to the designer for the analysis to find out the margin of safety for accepting it for end use. Finally it is concluded that through transmission technique is a valuable method that can provide useful information on structural integrity of the composite pressure vessel, once all the essential elements of the test are considered, approved procedures are followed and the test is carried out by qualified personnel. Acknowledgement The authors wish to express sincere acknowledgement of the support provided by Director, Advanced Systems Laboratory and Dr. Manoj Kumar Buragohain, Sc-G, Technology Director, CPDC for carrying out this work. References

Peters, S. T., Humphrey, W. D., Foral, R. F. “Filament Winding Composite Structure Fabrication”. Second Edition, Society for the Advancement of Material and Process Engineering (SAMPE).