Acoustic Emission AE Inspection
AE inspections are used to highlight structural weaknesses and cracks in pressure vessels, piping and tanks. Testing generally requires loading of a vessel or piping by filling with liquids or increasing the pressure. For most in-service equipment, the pressure or level is increased from 5% to 10% over the operating level while the AE is monitored and recorded. In some special applications, such as on-line monitoring and storage tank floor assessments, the AE signals are generated by the environmental conditions and no additional loading is required.
IRISNDT APPLIES AE
- To inspect pressure vessels, tanks and piping
- To inspect composite (FRP, GRP) Pressure Vessels, Tanks and Piping
- To inspect aboveground storage tank floors. AE in this case is very useful in surveying a number of tanks to help set inspection priorities and avoid unnecessary tank entries. The corrosion activity is graded from ‘I’ (little or no active damage) to ‘IV’ (very active damage)
- To inspect refrigerated ammonia tanks. AE is listed as a recommended non-intrusive test method in the European Fertilizer Manufacturers Association guidelines when internal inspections were carried out previously.
- For On-line Monitoring of suspect areas in pressure vessels and piping. The monitoring process is controlled and evaluated remotely from a IRISNDT office. AE sensors are installed and connected to instrumentation on site and controlled through an Internet connection. Thermocouple, pressure and other process data are recorded with the AE data.
- For Cooldown Testing. The AE sensors detect thermal stress generated in piping and vessels as a unit is shut down and cooled.
- AE is non-intrusive and can be performed on in-service equipment
- External AE testing is more cost effective than internal inspections
- AE assesses the equipment for structural problems, approximates where flaws are, and gives a measure of their severity
- In the case of ammonia tanks, with AE inspections one avoids the thermal stresses incurred during recommissioning and the risk of oxygen contamination incurred during internal inspections.
- AE assessments are qualitative; they do not characterize flaws or corrosion damage in terms of flaw, orientation, size and/or depth
- AE inspections are generally not sensitive to porosity, slag inclusions and small lack of fusion fabrication defects in operating equipment
- Background noise and other properties of a particular vessel may limit detection sensitivity
- A complementary inspection method, such as shear wave ultrasonics, is needed to map out and size flaws detected with AE
ACOUSTIC EMISSION FUNDAMENTALS
Acoustic Emission (AE) is high frequency sound generated by cracks and similar flaws in materials when stressed. Surface mounted, high frequency acoustic sensors detect AE signals generated by the test. The test procedure and AE data evaluation are designed to detect damage and provide a measure of a vessel’s response to the applied load. Structurally significant defects produce relatively intense acoustic emission activity when subjected to additional stress from filling or pressure.