Table of Content
- HDPE Inspection Challenges
- HDPE Wedge
- HDPE Sample and Artificial Defects
- Used Equipment and Accessories
- Scan Plan & Focal Law
- Semi-auto Encoded Data Collection
- Data Evaluation
- Results
- Conclusion
High-Density Polyethylene (HDPE) is an alternative material being adopted for industrial uses like the transportation of water for mining processes, low and medium-pressure gas lines, emergency fire systems, and class 3 nuclear piping systems. Price, high corrosion resistance, easy manipulation, transportation and handling (HDPE is a very light product), faster and easy welding process, flexibility, and other characteristics have made HDPE pipes popular in industrial and domestic facilities and it is a cost-effective replacement for metal pipes.
HDPE butt welds are manufactured in four stages: heating, heat soaking, heater plate removal, and joining-cooling. The heating stage involves the two prepared pipe sections of HDPE being pressed against a heater plate under specific pressure and being held there for a specific time (heat soaking). Thereafter, the heater plate is removed and the two ends are aligned exactly and brought together. The joining-cooling process involves the compression of the two faces together and being held for a specified duration in order to fuse the two ends. The excess material squeezed out during the butt fusion force forms a bead on the inner and outer surface of the weld leaving virtually no heat-affected zone in the weld.
Installation and joining of HDPE pipework sections happen on-site where environmental conditions may introduce impurities such as grease, dust, dirt and sand to both the heater plate and pipe ends. This type of contamination can lead to defects in the Butt Fusion Weld. The size of the air pocket created by the contaminants can produce a Lack of Fusion (LoF) where there is no bond or a partial bond between the faces of the sections. Generally, it is considered that any LoF present will occur perpendicular to the radial-axial plane i.e. 0° tilt. Kissing bonds or cold joints can occur when the contact that is made is not sufficient to form bonds capable of transmitting shear stress resulting in a lack of strength.
Classical Non-destructive Testing Methods as Radiography and Ultrasonic Shear Waves angle beam doesn’t’t show good results. The properties of this product make difficult to work with shear waves since attenuation of this waves is an issue in this type of materials.
In Article 4 of 2021 ASME BPVC Section V edition, the Ultrasonic Examination of fusion joint s of HDPE pipes has been included in the mandatory Appendix X.
As a result of the research presented in this paper, an inspection solution using phased arrays has been developed for detecting the artificial reflectors introduced into HDPE samples through the use of a new HDPE wedge developed by Olympus/Evident. This approach has been implemented to find defects in the entire volume of the weld.
HDPE Inspection Challenges
- High attenuation
- TOFD - Limitations
- Refracted angle issues with rexolite wedges
1. High Attenuation:
HDPE's high attenuation property prevents the use of shear waves for inspection
2. TOFD Limitations:
Time of Flight Diffraction (TOFD) technique has the ability to detect defects in the HDPE material, however this technique also has limitations such as.
- The deployment of TOFD requires access from both sides of the weld
- Single-side access welds/components cannot be inspected with TOFD 3. Dead zone issues
3. Refracted angle issues with Rexolite wedges:
The longitudinal velocity of sound in HDPE is around 2150 m/s to 2500 m/s like that of standard Rexolite wedges; this makes the generation of high-angle beams difficult
HDPE Wedge (SA32C-AQ-N55L-IH-HDPE)
Figure 1. The wedge has been developed by Olympus/Evident which will give 55 refracted angles in HDPE material.
HDPE Sample and Artificial Defects
Figure 2. HDPE sample with artificial defects
HDPE Equipment and Accessories
Figure 3. Equipment and accessories used for the inspection
Scan Plan & Focal Law
Figure 4. PAUT Scan plan for the inspection
Semi-auto Encoded Data Collection
Figure 5. Semi-auto encoded Data Collection A, C & S views
Data Evaluation
Actual defects comparison with PAUT Data:
Figure 6. Actual defects in the HDPE sample are shown in the PAUT Sectorial view
Results
Figure 7. Each defect depth is shown in the C, and S views along with measuring window
Conclusion
- Used an HDPE wedge produce a strong SNR improvement, helping to analyse the data clearly.
- The new implementation of the HDPE wedge & developed PAUT setup seems one of the better techniques for HDPE Butt Joints inspection
- The effectiveness of the wedge-refracted angle is giving the required direction to the beam-set
- 100 % volume(thickness) has been covered with the suggested technique
- Surface & sub-surface defects have been detected
- A compound beam set is given the effective results on various orientation defects.
Further Work
Further work is underway to find the defects in the actual weld sample of HDPE & Test results will be presented in the next publication.
References
1. ASTM E3044/E3044M−16, Standard Practice for Ultrasonic Testing of Polyethylene Butt Fusion Joints, Published by American Society for Testing and Materials
2. ASME Section V, Article 4, BPVC.V -2021
3. Ultrasonic TOFD Butt Fusion | Olympus IMS
4. Phased Array Instruments | Evident IMS
“It has been an absolute delight to collaborate with Shah Nagardas and work alongside such talented and supportive colleagues. I would like to extend my heartfelt gratitude to Mr. Anil Shah, Mr. Vikas Satore, and Mr. Sabri Baba (Evident) for their unwavering support and encouragement throughout this journey.
With the continued trust and backing of Shah Nagardas's leadership and management, our team remains committed to reaching new milestones and achieving even greater success.
My sincere thanks to OnestopNDT management and team for publishing this article, which contains very useful technical information for the NDT industry”
Author
Application Specialist
