The Plastic Pipe Database Committee (PPDC) has identified early life failures in electrofusion joints as a significant cause of pipeline failure. Similarly, a comprehensive study of electrofusion joints in the UK found that 20% of field joints sampled failed in destructive testing.
The primary causes of failure in this study were identified as:
- Inadequate clamping or misalignment: 34%
- Contamination: 29%
- Poor scraping: 26%
- Other: 11%
Proper qualification programs, proper installation procedures, and operator training best practices can significantly mitigate these potential failures. This is particularly true for issues of contamination and poor scraping.
JANA recognized that an effective and reliable non-destructive evaluation methodology would provide a valuable tool for inspection of joint quality to ensure pipeline integrity, providing the important ‘check’ function in the Plan – Do – Check – Act (PDCA) cycle. We began a research program to develop a better tool, based soundly on field experience in testing EF joints, and the result was jaNaDeTect™.
The Goal of jaNaDeTect™
The goal of ultrasonic inspection is to “see” the hidden regions of an electrofusion joint to assess joint quality. There are two primary ways that ultrasound can be used on plastic pipe joints. The first method is to use a pulse-echo system, using a single probe transducer and presentation of results in the form of an A-Scan (time domain trace). This is a very simple and inexpensive system using only one probe and modest electronics.
A typical A-Scan trace includes an X, Y plot showing energy received (Y-axis) vs. time (X-axis). Information from the material interfaces and other reflections are contained in the sinusoidal wave shape.
This led to the development of a simple-to-use, cost-effective and highly accurate tool – jaNaDeTect™ – based on A-scan technology. The key to this methodology is the development of a novel approach for analysis of the sound waves.
The sinusoidal waveform output from an A-scan contains a significant amount of information about the substrate through which the sound passes. Good welds with no defects produce a very distinctive sinusoidal trace where the ‘ring down’ from the wires is overlaid by the various weld reflections, resulting in slight changes to peak height and received frequency. Voids show up as additional peaks. Contamination produces very unique and easily identifiable waveforms.
Simple to Use
The jaNaDeTect™ hardware is portable and handheld while still being rugged enough to perform in the field. The jaNaDeTect™ hardware easily connects to a tablet or laptop and its patented software guides users through each electrofusion joint test, giving an overall pass/fail result for the joint.Analysis of a 4″ electrofusion coupling takes 5 – 15 minutes.
jaNaDeTect™ is hand-held, rugged and can be connected to a portable tablet or laptop. Given the very low profile of the end of the probe, it can be used in very tight areas and measure right up to shoulders and other molding irregularities. The probe needs to be in direct contact with the surface, which is achieved using a coupling gel.
The A-Scan output–a string of numbers representing the power received by the receiver in time increments–is processed to provide a green/red light for a pass or a fail of the joint. It is also possible to determine the type of void and, hence, the most likely cause of the joint failure so that corrective action can be taken. Roughly thirty readings are taken each second. Repeatability is excellent so averaging of the spectra is not required.
One requirement for A-scan technology is that the probe is held vertically to the weld to ensure maximum sound reflection. Even small deviations from the vertical can result in poor results, which may be one reason why A-Scans have not become popular. This issue has been resolved by the development of a patented software solution that ensures results cannot be taken until the probe is in the vertical position, confirming that the operator obtains an accurate assessment of the joint.
Low per-unit cost allows jaNaDeTect™ to be used widely in the field, affording gas distribution pipeline operators the ability to equip each fusion crew with joint inspection capabilities, providing a viable means of achieving 100% joint inspection.
jaNaDeTect™ has been verified for couplings and tees through testing of over 200 pipe joints of various diameters between 1″ – 20″. Excellent correlation has been achieved for all major defects found in electrofusion joints, including voids, contamination, cold fusion and more.
Specifically, jaNaDeTect™ can identify the following type of defects, giving a green/red light (pass/fail) indication:
Voids: Readily detected due to the PE-to-air interface, which produces a significant response where position on the x-axis of the spectra varies depending on the void location
Cold Zones: The area where there is a tight interference fit of the pipe inside the coupler but not within the fusion zone. There are two interfaces (the pipe and the EF fitting) with a very small air gap between. This gives significant peaks, which are impossible to misinterpret. Their position on the x-axis of the spectra is fixed with respect to EF fitting thickness
Contamination: Assessed through a novel spectral analysis methodology and correlated with reference spectra and destructive testing to provide a green/red (pass/fail) response. Contamination results in the PE in the coupler and the pipe not flowing into each other sufficiently to enable chain entanglement during the melt phase of the welding. This results in a specific spectral pattern.