Acoustic Emission Testing
Fiberglass Tanks and Vessels
The recommended practice for acoustic emission testing of fiberglass tanks and vessels was first published in January 1982. This was the result of several years work by The Society of the Plastics Industry's Committee on Acoustic Emission from Reinforced Plastics (CARP). The published procedures and evaluation criteria were based on hundreds of tests of in-service vessels, new equipment and laboratory studies. It was probably the first acoustic emission test procedure that included clear, consistent testing and evaluation rules.
Other organizations (ASME, ASTM) have used the CARP document as a model for development of testing practices for metal vessels as well as fiberglass equipment. An example of this is ASME Section V, Article 11 and RTP-1-1992.
There is no accurate count of the tests conducted under this procedure. However, it is estimated that this number is in excess of 10,000, making the method as routine as some of the long standing NDE methods.
This does not mean that this technology is stagnant though. The CARP committee still meets to review current results and new developments, Several improvements and updates to the procedure are in progress.
A test of this type provides a measure of a tank or vessel's response to service loads. As such it gives an overall evaluation of a vessel or piping and highlights any areas of weakness. An area producing significant acoustic emission activity requires investigation to determine the nature of the problem and possible need for repair or change in operating conditions. On the other hand, vessels in good condition produce little activity and easily pass the criteria.
TEST
PROCEDURE
The procedure for testing FRP vessels is essentially
simple but attention to detail is essential. In-service
equipment requires conditioning prior to testing. This
means keeping the tank at a reduced level for some time
(a day or more depending on the level prior to the test).
Then, between eight and sixteen acoustic sensors are
attached using hot glue or tape; the AE system is
calibrated and background noise minimized, then the
vessel is loaded. For most tanks this is a matter of
filling to the 100% level with water or the process
fluid. There is no requirement for an overload as is
often the case with metal vessels.
The premise behind this procedure is that damaged or deteriorating FRP materials produce acoustic emission when loaded. In practice, all vessels produce a certain amount of acoustic emission and the role of the evaluation criteria is to separate a 'good' vessel from one that is in need of repair.
This is well supported by test data both from the laboratory and thousands of tests in the field. However, the AE test can only go so far and vessels failing to meet the criteria require further inspection effort to identify the problem or more frequent testing to track the rate of deterioration.
PRACTICAL MATTERS
What do I need to do in preparation?
 | The vessel needs to be empty or operated at a reduced level prior to testing. We prefer to start the test at a level of 30-40% or less. Parking and power for our test unit are very important (two 110V lines supplying 20A each from separate circuits); provision of a level gauge and means of filling or pressurizing the vessel under Matrix's supervision and access (ladders, scaffolding) to the vessel for sensor placement are the key provisions for this type of test. We find the cost and quality of the test are directly related to the level of communication and planning in advance of the test. |
| For most FRP equipment the site time is one or two days. This includes time for safety and planning meetings, equipment set up, testing and packing up. Being able to fill the vessel in a reasonable time with minimal noise is very important. We normally plan for a testing time of three to four hours. |
When do I get my results?
| In most cases the test results are available the next day with a formal report following within two to three weeks. |
What will the test tell me?
| The results will show whether the vessel passed or failed the evaluation criteria and the significance of any activity. The recently introduced intensity analysis gives a measure of the level and urgency of any follow-up actions needed. Typically our recommendations range from "Note this area for future inspections" through "re-test in one (or more) years" to immediate inspection of an area. Another common option for a deteriorating vessel is to operate it at a reduced level. |
Last updated:
September 06, 2002UT Tanks Technical Papers Conventions Email