PL Non-Piggable Pipelines

Take note

This overview will explain how to use the (Non-Pigable Pipelines) NPP module in the IMS PLSS. The NPP Module is part of the FSS Module.

Before creating a new NPP case, the following steps must be completed:

• Fill in all the Design data and make sure that:

  • On the Equipment Details Page, in the Design section, from the Piggability drop down menu select “Non piggable (in current confgurantion)”.

  • Tick the NPP mode checkbox.

• Perform the Internal and External Corrosion assessment, thus specify a Future and Past Corrosion Rate, and Final approve the ECH.

• Perform the RBA.

Non-Piggable Piplines Analysis

NPP is a five step process:

1. Determine Confidence of integrity information.

2. Calculate β.

3. Determine Inspection Coverage.

4. Recalculate β.

5. Determine the Integrity Status of the Pipeline and schedule the next Inspection.

Step 1: Determine Confidence of Integrity Information

Before the Confidence of integrity can be determined, a new NPP case should be created. To create a new NPP Case:

• Navigate to the FFS module.

• Select the NPP tab.

• In the NPP case date grid, click the Plus button.

• In the NPP Case Date field, enter the date.

• Click Save.

On the right side from the NPP case date section, the Questionnaire (NPP) will appear. To fill in the questionnaire:

• Click Edit.

• Select the applicable answer to each question.

• Click Save.

If the score of the Confidence Rating is Very Low or Low then at least 10% of the total length of the pipeline or flow line should be inspected, see the overview in the previous section. If the score gives a Medium, High, or Very High Confidence Rating then carefully define the zones of potential degradation and determine the β for each zone.

Step 2: Calculate β and Degradation Stage

For Non-piggable pipelines, determining the required amount of inspection is challenging. The proposed approach is based on three main elements:

• The Confidence Rating of current integrity information.

• The creation of logical degradation-based zones for inspection and analysis.

• For cases where information Confidence is High or Medium, i.e. where Degradation Mechanisms have at least been identified by Inspection, three “stages” of the Degradation Mechanism(s) are linked to the estimated Remaining line Life.

The three stages, Type A, B or C, of the degradation for the High/Medium Confidence Rating are defined as follows:

1. In the early part of the designated line lifetime, where degradation is thought to be taking place but where inspection has not detected any defects.

2. In the mid-period of the designated line lifetime, where defects have been detected but are estimated not to become unacceptable for some time.

3. In the later part of the designated line lifetime, where the defects detected are likely to become unacceptable in the short to medium term.

The estimated time remaining, from a specific point, until the Degradation Mechanism reduces the Pipe Wall Thickness below the Minimum Acceptable Wall Thickness (MAT) is referred to as Remnant Life (RL).

For each designated degradation zone, integrity information is used to assess the degradation rate and tolerance. For the cases of Internal or External Corrosion, the two most common Degradation Mechanisms, the Corrosion Tolerance (CT) can be calculated with PLSS using a certain assumed worst-case defect aspect ratio.

First, the inspection regime applicable to the different pipeline degradation stages needs to be determined for each identified zone. These regimes are shown diagrammatically in the figure below.

In this figure, the lower left boxes have the following meaning:

• Compliance: confirmation of the assumption that there are no detectable defects in a degradation zone.

• Estimation: estimation of the size of the worst defect(s) in a degradation zone based on a limited sample of that zone.

• Find them: detect all significant defects in the complete zone to determine the Remnant Life.

The particular inspection regime is determined by the ratio β, which is the ratio of Defect Depth over Design Corrosion Tolerance:

Where:

• d: Defect depth (measured or estimated)

• MAT: Minimum acceptable thickness

• CT: Corrosion Tolerance = WT-MAT

• CT_design: Original Corrosion Tolerance at commissioning using Fitness-for-Purpose, the expected defect aspect ratio, and the current MAOP.

  Note: In the absence of firm defect morphology knowledge, the default Defect aspect ratio should assume infinitely long Defects. In other words, MAT must be determined from the current MAOP and then CT is given by “uncorroded” Wall Thickness minus MAT

To enter the data into the Internal NPP section:

• Click on the Down arrow to open the Internal NPP section.

• Click the (Re)Generate button.

Clicking the (Re)generate button will populate the Internal NPP grid with the data and calculate the β (pre) value and the Stage.

The most important data shown in the grid is explained in the table below:

To determine the Stage for the External corrosion, repeat Step 2 explained above for the External NPP grid.

The conclusion after calculating β is shown in the Status bar.

Step 3: Enter Inspection Data

After calculating the Stage, proceed to complete the Sample Inspection. You should inspect at least the suggested coverage.

Once the Sample Inspection is completed, enter Inspection data into IMS PLSS, including any detected Defects, into the Assessment tab.

Take note

Once the Defects are added remember to Final Approve the ECH.

Step 4: Recalculate β

After the Defects have been entered, proceed to fill in the the coverages in the Internal and External NPP sections.

• Click on the down-arrow button to expand the Internal or External NPP section.

• Click Edit in the grid.

• In the Overriden coverage enter the percentage of the Pipeline the Inspection covered.

• Click Save.

• Click (Re)Generate.

This will populate the β(post) and Stage columns with the data and update the Information Bar. Note: If the percentage of covarge is too low, the information bar will indicate “(Insufficient coverage)” next to the Stage.

Step 5: Determine the Integrity status and NID

Based on the β(post) value, check if your Stage (coverage) is sufficient. If yes perform the FFS analysis using the Inspection results. If not inspect more coverage based on the β(post) Stage.

Evaluate the sufficiency of your inspection coverage based on the calculated β(post) value.

If the coverage is deemed insufficient:

• Perform a new Inspection with expanded scope and repeat steps 3 to 5.

If the coverage meets the required threshold:

• Proceed with the Fitness-for-Service (FFS) analysis using the obtained inspection results.

To see the overview with all the steps, click the Diagram button.