statistically active corrosion_ lite
DESCRIPTION
A DNV Columbus Integrity Tool. 07 August 2009 Points = Average Depth for the Joint Error Bars = Variability of Depths for the Joint This screen shows a preliminary analysis of 41 joints. While there is deep corrosion on three joints, the average depth and variability of the 2003 and 2008 ILI results are nearly identical. So, there appears to be no active corrosion. Joint Number Depth Calls > 50% © Det Norske Veritas AS. All rights reserved.TRANSCRIPT
07 August 2009
Statistically Active Corrosion AssessmentsA DNV Columbus Integrity Tool.
© Det Norske Veritas AS. All rights reserved.
Friday, 07 August 2009
2
Step 1: Compare Defects in Each Joint
Calls > 50%
Points = Average Depth for the Joint
Error Bars = Variability of Depths for the Joint
Joint Number
DepthThis screen shows a preliminary analysis of 41 joints. While there is deep corrosion on three joints, the average depth and variability of the 2003 and 2008 ILI results are nearly identical. So, there appears to be no active corrosion.
© Det Norske Veritas AS. All rights reserved.
Friday, 07 August 2009
3
Step 2: Identify Outliers
Joint Number
Depth
Here are several joints with deep corrosion (the middle joint was sleeved). It could be active. A Statistically Active Corrosion (SAC) analysis will tell if some of the anomalies in each joint are growing.
© Det Norske Veritas AS. All rights reserved.
Friday, 07 August 2009
4
Step 3: Look for New Corrosion
Joint Number
Depth
Here, we have new corrosion, but it’s mostly shallow. A Statistically Active Corrosion (SAC) analysis will determine an effective growth rate, which can then be used to estimate remaining lives.
© Det Norske Veritas AS. All rights reserved.
Friday, 07 August 2009
5
Step 4: Growth
Joint Number
Depth
These indications might be growing, but the error bands overlap somewhat. It’s not clear whether there is active growth. SAC will identify joints like these for further analysis, which could include comparisons of the actual MFL signals.
© Det Norske Veritas AS. All rights reserved.
Friday, 07 August 2009
6
Step 5. Check Areas with High Growth Rates This looks like new deep
corrosion – we check the MFL features lists and compare the MFL signals. Sometimes, they show there were defects in the earlier data that were not reported or were reported as something else (e.g., internal not external).
© Det Norske Veritas AS. All rights reserved.
Friday, 07 August 2009
7
SAC Summary SAC refers to a Statistically Active Corrosion assessment.
SAC creates and compares distributions of features from two (or more) inspections over a window.
When the distributions show evidence of change, the differences are analyzed to estimate growth rates.
Checks and balances weed out outliers and problem data.
© Det Norske Veritas AS. All rights reserved.
Friday, 07 August 2009
8
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