Corrosion under pipe support inspection by advanced ultrasonic method

Corrosion under pipe support inspection by new advanced ultrasonic method 

#CUPS  #PA-CAT  #QSR  #Corrosion #Corrosion under pipe support #Quantitative Short Range #Ultrasonic testing

AUTHOR: Vittawas Bunjang

Introduction

     Corrosion under pipe support (CUPS) is a significant issue affecting the integrity and reliability of pipelines, particularly in regions like Maptaput, where over 50,000 pipelines have been in operation for more than 20 years. This problem contributes to unplanned downtimes, with approximately 44% of aged pipelines being affected. The resulting impact includes high maintenance costs due to sectional replacements and significant environmental risks from potential pipeline leaks.

     Corrosion under pipe support (CUPS) is a critical issue that arises from the way pipes are supported and the environmental conditions they are exposed to. The process begins with crevices inherent by design or natural formation, which trap moisture. This moisture entrapment and hold-up result in coating failure, exposing the metal surface to corrosive elements. Over time, corrosion occurs, leading to potential failure and loss of containment, posing significant risks to both the environment and the pipeline's integrity.

Figure 1. The Cause of Corrosion Under Pipe Support (CUPS).

Technical detail:

     The current methods for inspecting CUPS damage, such as visual inspection, medium-range ultrasonic testing (MRUT), and long-range ultrasonic testing (LRUT), present challenges.

1.     Visual inspections often rely on brute force approaches and require lifting pipes for accurate measurements, leading to false calls.

2.     Medium range ultrasonic testing (MRUT), and Long range ultrasonic testing (LRUT) techniques, while more advanced, are primarily used for screening and prioritizing further inspections. Therefore, both of these methods are inadequate for troubleshooting CUPS issues.

Figure 2. Long range ultrasonic testing can produce similar amplitude signals even when the volume of corrosion in a pipe varies.

Figure 3. LRUT and VT cannot determine the remaining pipe thickness, rendering the data unsuitable for decision-making.

     In corrosion under pipe support problem, advanced ultrasonic testing methods, such as Quantitative Short Range Ultrasonic Testing (QSR1) and Phased Array– Composite Angle Technique (PA-CAT), offer the most effective means for detection, remaining wall thickness measurement, and suitability for on-stream inspection.

     The QSR1 (Quantitative Short Range Ultrasonic Testing) inspection technique utilizes guided wave technology to effectively detect, size, and monitor corrosion and erosion in steel pipes. This innovative system focuses on frequency analysis to provide quantitative measurements of the minimum remaining wall thickness, as well as axial and circumferential lengths. Known for its reliability, repeatability, and accuracy, QSR1 simplifies complex inspection procedures and eliminates the need for pipe removal, offering significant time and cost savings while ensuring the fitness for service.

Figure 4. Schematics showing:

(a) the instrument on the pipe and the two main wave paths and

(b) the model of the unwrapped pipe used in finite element simulations extended clockwise (to the right) and anti-clockwise (to the left) with respect to the transmitter (in the middle) to give multiple transits around the circumference. T is the transmitter with notional receivers placed clockwise at A, A+C, etc, and anti-clockwise at B, B+C, etc, to give different received wave packets at these points.

The PA-CAT™ (Phased Array– Composite Angle Technique) system is an innovative inspection method that relies on amplitude-based signal attenuation between two phased array transducers in a pitch-catch configuration. This technique uses all available shear wave angles to provide quantitative measurements of the minimum remaining wall thickness, as well as axial and circumferential lengths. By focusing on amplitude changes, PA-CAT™ enhances the accuracy and reliability of corrosion assessments, making it a valuable tool for maintaining pipeline integrity.

Figure 5. PA-CAT™ is primarily amplitude-based and uses: Phased array and all available shear wave angles.

Corrosion under pipe support inspection results

Figure 6. QSR1 scan shows the pipe support section is in good condition

Figure 7. QSR1 scan shows the deepest corrosion depth was found to be at 1.9 mm deep (~26.7% wall loss), with a minimum remaining wall thickness of 5.2 mm. 

Figure 8. PA-CAT™ scan shows the deepest corrosion depth was found to be at 6.529 mm deep (~91.83% wall loss), with a minimum remaining wall thickness of 0.581 mm.

On-Field Practice (On-stream Inspection)

Figure 9. Comparison of QSR1 Results with Corrosion Depth Measurements Obtained by Pipe Lifting.

     Our field experiments demonstrate the efficacy of our methodologies and advanced technologies in accurately identifying both sound and damaged pipe sections affected by CUPS. The images above illustrate a sound pipe section and one with corrosion, as indicated in the QSR1 and PA-CAT systems. The superimposed 2D pipe image precisely locates the area of corrosion. Following the ultrasonic inspection, our team conducted further verification and confirmed the corrosion presence, validating the findings of our advanced ultrasonic inspection methods using QSR1 and PA-CAT.

Technical Summary:

1.     Visual Inspection (VT): Primarily used for pre-screening to identify CUPS (Corrosion Under Pipe Supports) damage, but it cannot determine the remaining pipe thickness.

2.     Long-Range Ultrasonic Testing (LRUT) / Medium-Range Ultrasonic Testing (MRUT): Effective for pre-screening and detecting CUPS damage over a wide range. However, these methods cannot determine the remaining pipe thickness.

3.     QSR1 and PA-CAT: These methods offer the most effective means for CUPS detection, accurate remaining wall thickness measurement, and are suitable for on-stream inspection.

Key benefits:

Quantitative: Measure minimum remaining wall thickness, axial length and circumferential length.

Reliable, Repeatable and Accurate: Measure minimum remaining wall thickness shown in axial length and circumferential length to calculate remaining life of pipe.

On-Stream Inspection: Ultrasonic methods can often be applied without taking pipe offline and without the need to lift up pipe, minimizing disruptions to operations.

Versatility: QSR1 can be adapted to inspect soil to air and concreate to air damage.

Environmental Friendliness: As a non-destructive testing method, ultrasonic testing avoids the need for destructive sampling or the generation of hazardous waste, contributing to a more sustainable inspection process.