Pipeline Leak Detection using Acoustic Emission

 

Tested Structures:

  • Main pipeline

  • Aerial, river, road and railway bed crossings

  • Pipes of pumping and compressor stations, gas distributing stations

Applications and Usage:

  • Testing when in service:
     - Annual testing
    -     Continuous monitoring

  • Testing when lowering pipeline in

  • During hydrotest

  • Before major repair

Defects Identified:

  • Cracks, lack of penetration, under-cuts, inclusions, edge displacements in butt welding

  • Corrosion

  • Laminations

  • Leaks

  • Ice plugs

also:

  • External noise / safety (drilling, hammering etc.)

Advantages:

  • Testing is performed during operating conditions  

  • Inspection of whole structure

  • Inspection of areas not possible with other NDT techniques

  • Minimum access to surface for sensors mounting

  • Distant location of flaws

  • Very efficient method of testing

  • Sensitive to growing defects, i.e. most dangerous flaws are detected

Questions for Practical Applications

 

1. What is the minimum leak to be detectable?

Depending on the type of fluid, the pressure difference across the defect, the size of the defect and the instrument. Minimum 0.3 ml/sec was reported. Generally, 1-10 ml/sec for liquid or 10-20 ml/sec for gas is more practical.

 

2. What is the optimum space between two sensors for leak detection?

Depending on materials under test, the leak rate, the type of fluid, the pressure difference across the defect, the size of the defect and the instrument. There is a trade off between the detectable leak rate and the space. Maximum 250m was reported. 50 – 125m is usual.

 

3. What is the frequency bandwidth which is suitable for leak detection?

Generally, the frequency of the leak noise has a character of wide bandwidth. The sensors with the resonant frequency between 30 - 400 KHz were frequently used.

 

4. How efficient for underground pipeline leak detection?

1-2 kilometers/day is not unusual.