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Stress Corrosion Cracking Assessment in Pipeline Mohammed Abu Four October 11, 2010

2. Outline Introduction Objective
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Outline
Introduction
Objective
Schematic of Stress Corrosion Cracking (SCC)
When does SCC occur?
Challenge of detecting SCC
SCC Assessment at pipeline (Case study)
Detection utilizing Advanced Ultrasonic systems
Conclusions
The outline of my presentation as the following. I will start with introduction

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Introduction
In Middle East region, thousands of kilometers of pipelines are carrying many kinds of fluids, anything from water to crude oil. It is estimated that over 75% of pipelines are buried, and therefore subjected to environmental abuse, external damage, coating de-lamination, soil movements/instability, and attack by external stress corrosion cracking.

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Objective
To determine a suitable advanced NDT technology in detecting stress corrosion cracking in order to avoid serious leaks or ruptures and to ensure the reliability of Pipelines

5. Objective Goals Enhance environment safety Proactive prevent failures
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Objective Goals
Enhance environment safety
Proactive prevent failures
Improve pipeline integrity
To assist Pipeline integrity and SCC location identification for replacement and future repair.

6. Background
Stress corrosion cracking (SCC) is a form of localized damage that refers to cracking under the combined influence of tensile stress and a corrosive environment.

7. Schematic view of Stress Corrosion Cracking (SCC)
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Schematic view of Stress Corrosion Cracking (SCC)
SCC is believed to be at pitting damage sites and develops under the action of local tensile stresses as a highly branched network of fine cracks.
At each crack tip the combined action of the tensile stress and specific ions in the
corrosive media cause continual crack propagation with little evidence of local deformation.

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When does SCC occur?
Stress corrosion cracking presents an especially difficult problem, not just because it is highly localized, but also it can occur in environments that are merely mildly corrosive to the material.
The damaging concentration of the harmful ions in that environment may be quite small and difficult to detect and, even in the absence of applied stress, residual stresses in a structure can often be of a sufficiently high level to cause SCC and failure in service.

9. SCC Detection challenge
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SCC Detection challenge
Stress corrosion cracking is generally considered to be the most complex of all corrosion types. SCC is classified as a catastrophic form of corrosion, as the detection of such fine cracks can be very difficult and the damage cannot easily be predicted. As I said at the beginning, It is very difficult because we are looking for cracks at level of crystal grains size.

10. Case study Crude Oil liquid pipeline 16 inch diameter
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Case study
Crude Oil liquid pipeline
16 inch diameter
49 kilometer long
Material is C/S, W.T. 9.5 mm
Type of pipe is ERW
Build in 1952

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Initial Inspection
Electro Magnetic Acoustic Transducer (EMAT) technology was utilized and result recorded many indications with a linear reflection caused by crack like anomaly.

12. EMAT Inspection results
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EMAT Inspection results
EMAT inspection provide useful information such as distance from the start up, clock position of the indication, joint number and type of the indication.

13. What Is Non-Destructive Testing?
Nondestructive testing is an examination performed on any type of test object without changing or altering that object in any way

14. What Is Advanced Non-Destructive Testing?
Advanced Non-Destructive Testing is an examination performed on any type of test and all the data are analyzed and recorded by computers

15. Phased Array Ultrasonic Inspection
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Phased Array Ultrasonic Inspection
Phased Array is a precision ultrasonic system that can give high accuracy of flaw height and width of in-service flaws.

16. Why we used Phased Array ultrasonic system?
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Why we used Phased Array ultrasonic system?
Provide accurate sizing & measurements
more than any other UT equipments
Provide 4-D images (permanent record)
Faster inspection
Because it

17. What Are Ultrasonic Phased Arrays?
PA probe consists of many small ultrasonic elements, each of which can be pulsed individually
The beam is swept like a search-light through the tissue or object being examined, and the data from multiple beams are put together to make a visual image showing a slice through the object.
sound beam through a range of refracted angles or along a linear path, or dynamically focus at a number of different depths, thus increasing both flexibility and capability in inspection setups.

18. What are Ultrasonic Phased Arrays?
Ultrasonic phased arrays use a multiple element probe whereby the output pulse from
each element is time delayed in such a way  to produce constructive interference at a
specific angle and a specific depth.
These time delays can be incremented over a range of angles to sweep the beam over the
desired angular range. For example, 40 to 75 degree beam sweep would be produced by
calculating the time delays to produce constructive interference at 40, 41,
degrees. This NDT technology is also referred to as Swept Beam Ultrasonic testing.

19. Advantages of phased array
Ability to sweep a range of angles
Ability to display the image in real time for the swept angles
Ability to focus

20. Phased Array Technology = S-Scan (Sectorial Scanning)65 35 45 55
Delays 40 75

21. Phased Array Calibration

22. Phased Array Set-up

23. Phased Array Sensitivity Set-up
EDM Slot Sizing Block
This block contains nine EDM slots from 0.050" to 0.900" deep. Slot width is 0.011". Nominal depth is laser engraved on the side of the block.

24. Phased Array results SCC almost connected through the W..T
SCC connected to OD surface

25. SCC almost connected through the W..T
Phased Array result
SCC almost connected through the W..T

26. Outer Surface of the pipe
Phased Array result
Two SCC connected to the OD
SCC at OD surface
SCC at OD surface
Outer Surface of the pipe

27. Phased Array result
SCC at OD surface

28. Visual & Magmatic Particle Inspection Result

29. Conclusion
Advanced NDT technology is the best way to ensure safety and reliability of the pipeline
Phased Array ultrasonic technique confirms the present of stress corrosion cracking
Stress corrosion cracking open to surface and OD surface cracks were confirmed by Magnetic particle inspection
Affected spools were removed and pipeline was put back on service

30. Thank you