Composite pressure tanks are more and more used as an alternative to conventional pressure tanks made of steel and aluminium. Due to its stability and light weight construction there will be a continuing high appeal in the future for the use of carbon pressure vessels. To ensure high quality from production to end-user, fast and reliable NDT solutions are required.
This application note details the use of non-contact shearography method for quality assurance on a type 3, 6, 8 l composite pressure vessel demonstrator as it is used by fire fighters for breathing protection. The use of shearography is also enabled for all other tanks or composite pressure vessels. In order to produce a realistic case of damage, the tank was dropped from the norm height of 1.8 m in two inclinations, so that 2 defect fields were produced on the tank. The composite vessel was loaded via internal pressure in a special pressure vessel loading container shown in the image below. The test was carried out at Federal German Test Institute (BAM). As loading medium, water was used.
For the measurement a pressure release approach was used. The shearography method requires two images, one reference image and one loading image. Reference pressure on the test was 100 bar (1450 psi) and differential pressure release for the loading image was 0,5 bar (7,25 psi). In all displayed measurement cases, this measurement parameter arrangement showed good results, but other reference pressure-loading arrangements are also possible. The drop test with positive inclination of 45° showed that the front peak was affected also by an impact that was measured and displayed in a different measurement set-up.
The section cut analysis shows the gradient information of shearography measurement and gives an indication of signal to noise ration and the possibility of verification of defects. Metric analysis is also needed for determination the extension of the defect. Two measure tape lines show the approx. diameter of the two defects on the left area with 15.3 mm and 18.7 mm on the right area.
Inspections with a full-field, non-contact methods show that the shearography method is able to cope with the task of fast detection of material defects (Impacts, etc.) in pressure vessels. The used sensor configuration enables also an effective and affordable solution to possible end-users. Especially speed is the main advantage of the shearography method. Measurements on this pressure vessel were carried out in less than 10 seconds. That enables the possibility to provide a reliable method with all displayed advantages for quality assurance to the industry.