Introduction

The invention refers to procedure able to verify the integrity of underground LPG tanks, carried out with a methodology based on the analysis of the Acoustic Emission signals that characterise the elastic tension waves associated with a rapid release of energy by every discontinuity (source) that is present in the tank structure.

Technical features

The sector regulation provides the execution of an integrity check of the underground LPG tanks every ten years. These checks can be carried out by putting the tank out of service and digging it out (with obvious inconvenience to the user), or by means of an Acoustic Emission test that requires simply access to part emerging from the ground and therefore does not require commissioning the tank out of service.
The technique used for the Acoustic Emission method application is schematically referable to the following phases: solicitation by pressurisation of the tank structure; constant pressure rate control using a suitable sensor; detection of the acoustic activity produced by the application of pressurisation using sensors of appropriate characteristics installed on the accessible part of the structure; elaboration and interpretation of the Acoustic Emission signals used calculating two evaluation indices and of the related synthetic indicator; tank classification. One of the most critical phases is the pressurisation of the tank: it must take place gradually, both for safety reasons and to avoid introducing spurious signals or noise. The test must be performed by qualified and certified personnel.

Possible Applications

• Detection of cracks, corrosion phenomena, welding defects and material embrittlement;
• Structural monitoring of equipment containing pressurised fluids;
• Monitoring the integrity of civil structures and infrastructures

Advantages

• Acoustic Emission method is particularly sensitive to the release of elastic energy associated with defects that evolve;
• Suitable for large structures;
• Possible to perform the test without decommissioning the equipment.