PL ILI Comparison - Girth Weld Matching Data

Take Note

This overview will explain how to read the data in the right upper pane of the ILI Comparison module.

The Right Upper Pane of the ILI Comparison module is dedicated to presenting the Girth Weld Matching data, an essential aspect of your In-Line Inspection (ILI) analysis. This article focuses on the automated Girth Weld match algorithm, which identifies and aligns Girth Welds from the compared ILI runs to enhance the reliability of Defect location accuracy. Given the potential for cumulative errors in odometer readings, it is crucial to verify the quality of the Girth Weld matches before proceeding to the automated Defect Matching step.

Automated girth Weld Match

The absolute distance reported by the odometer between different ILI runs along the same route could have a cumulative error of up to ±1% of the traveled distance. For a 10 km Pipeline, this translates to a location accuracy of ±100m. Even when an Above Ground Marker (AGM) is used as a reference point to improve the location accuracy, for a typical AGM spatial interval of 2 km, the Defect location accuracy is still not sufficient for the Defect matching. The first step in the ILI Comparison algorithm is to identify and match the same Girth Weld in compared ILI runs and use them as reference points to improve the defect location accuracy.

The Girth Weld Distance List could be extracted from the pipe tally spreadsheet listing all Pipeline Components and Anomaly features. Alternatively, it could be requested from the ILI vendor.

The ILI Comparison algorithm identifies and matches the same Girth Weld by comparing the spool length difference between compared ILI runs against the parameter Odometer Tracking Accuracy(OTA) (default: 5%). If the algorithm finds that a spool has a length difference less than OTA, it will match both Girth Welds of this spool. On the contrary, if the algorithm finds that a spool has a length difference greater than OTA, it will automatically skip the current spool and look for the next one, until the spool length difference falls again below OTA.

A default value of 5% is recommended for OTA. ILI vendors usually state that their Odometer Tracking Accuracy is ±1% over the traveled distance. This accuracy is achievable over a long traveled distance. However, for a single spool that could be as short as 0.5m, even if the absolute distance difference is small, the relative error could be well above 1%, i.e. 5mm. For this reason, a default slightly higher threshold of 5% is recommended in the algorithm.

In the example below, in column

A: The girth weld distance of Run Old (the first run), in meters.

B: The girth weld distance for Run New

C: The difference between the girth welds from column A (formula for range C2=A3-A2)

D: The difference between the girth welds from column B (formula for range D2=B3-B2)

E: The OTA, formula for range E2=Abs(C2/D2 – 1)*100%

If the OTA is set to 5% then the data in rows 4 and 5, for which the OTA is greater than 5% will not be matched and girth welds will be skipped. If you want to use a manual girth weld match that includes these welds, set the OTA to 100% to ensure all matches are considered.

Occasionally, girth weld locations may differ between compared ILI runs due to spool repair or replacement on the Pipeline. Another common scenario is that two ILIs may not start and end at the same location but are Offset by one or two Girth welds. The automated Girth Weld match algorithm has capabilities to handle these special cases. The figure below shows four different cases where the algorithm can make automatic correction and continue the girth weld matching work.

Example case B/D:

In the new run, a girth weld at 40 meters is present. On the right side, we see that this girth weld is ignored by the girth weld match algorithm.

The pane in the right upper pane contains four tabs:

• GW Offset

• Table Unmatched Spool

• Table GW Matched

• Table GW

GW Offset

The automated Girth Weld match algorithm generally works well. However, before proceeding to the automated Defect match step, you should check the Girth Weld match quality by viewing the figure in the GW Offset tab and signing off this step. The blue curve in the diagram shows the differences in Girth Weld Offsets between the two compared ILI runs, referred to as "ILI Run 1" and "ILI Run 2."

Example:

The diagram in the figure below shows no abrupt changes, which might be an indication that the match is correct.

Example:

In the diagram on the image below, an abrupt change is seen which indicates an incorrect match.  This could happen when substantial repair work has been performed on the Pipeline between compared ILI runs. At 3 km, this pipeline is shortened by 16m over the original length of 193m between two ILI runs. The spools within this area do not match between two ILI runs. The automated Girth Weld match algorithm is not designed to handle this unusual scenario.

Note: In the tab Table GW Matched you have the option to upload your own manual weld match list to proceed with the analysis.

Table GW Unmatched

The Table GW Unmatched contains four columns. The Old From and Old To columns list the Girth Welds for ILI Run 1, while the New From and New To columns displays those for ILI Run 2.

Example:

In the example from the image above, there are several Girth Welds in the input data between 9864.431 m and 9880.435 m for which no match has been found. Specifically, the Girth Weld at 9864.431 m in ILI Run 1 corrisponds to the one at 9862.847 m in ILI Run 2, and the Girth Weld at 9880.435 m matches with the one at 9878.861 m from ILI Run 2.

A total overview of the matched and unmatched girth welds are described in tab Table GW. Here we will see:

Table Matched GW

The Table Matched GW tab contains the Girth Welds that match. The first column shows the Distance of Run 1, the second column of Run 2.

Adding a Girth Weld Match

The Table GW Matched tab allows you to add a Girth Weld match manually. To add a Girth Weld match:

• Click the Plus button.

• In the GW Distance Run 1 field, enter the distance of the Girth Weld in the first ILI Run.

• In the GW Distance Run 2 field, enter the distance f the Girst Weld in the second ILI Run.

• Click Save.

Editing a Girth Weld Match

To edit a Girth Weld Match:

• Click the Edit button on the left of the GW Match.

• Change the values in the applicable field(s).

• Click Save.

Table GW

The Table GW tab contains all the GW data. If a cell is empty, it indicates that no match was found. For instance, in the example below, there is a Girth Weld at 0.3 m in Run 2, but no corresponding match exists in Run 1.