Optimising burst pressure rates

Asset owners often rely on conservative methods for integrity evaluations due to their simplicity and familiarity, even though they involve excessive safety factors.

However, in the context of ageing infrastructure, asset owners face more pipelines requiring inspection and repair than their available human and financial resources can manage. To cope, they must prioritise and address only necessary repairs, while avoiding unnecessary work.

Level I, II, and III assessments

Asset owners decide to comply with Levels I, II, or III based on the complexity and accuracy required to assess the asset’s condition and the associated costs and time constraints.

Level I analysis for burst pressure is for simplified and conservative assessments. Requiring minimal data, it is primarily used for early-stage assessments or for straightforward pipeline defects. Level II provides more detailed analysis with refined estimates, typically used for complex defects requiring a moderately conservative approach. This level allows the owner to reduce some of the excessive conservatism present in Level I, resulting in more accurate pressure estimate for more complex or critical defects.

Level III, on the other hand, uses advanced tools like FEA for precise calculations in high-risk pipelines, offering the most accurate burst pressure estimates. This level is chosen for complex, high-risk pipelines where precision is critical, and failure could have significant safety, environmental, or financial consequences.

Comparison of burst pressure calculation: FEA simulation (Level III) vs. analytic method (Level II)

Creaform tested four pipeline samples to compare burst pressures using different methods. The maximum operating pressures of these pipeline samples were then calculated using five techniques:

• B31.G Standard.
• B31.G Modified Standard.
• B31.G Standard – Effective Area.
• PSQR.
• FEA Simulation.

Method for burst pressure analysis

B31.G standard

The B31.G standard focuses on evaluating the severity of metal loss due to corrosion and other defects and helps determine whether a pipeline can continue to operate safely or if repairs or replacements are necessary. It provides guidelines for calculating the remaining strength and safe operating pressure of corroded pipelines.

The B31.G method calculates a “safe operating pressure” based on factors such as:

• Size and depth of the corrosion defect.
• Original wall thickness and diameter of the pipeline.
• Material properties of the pipe.

The B31.G standard is integrated into VXintegrity’s Pipeline module.

The results obtained with the B31.G standard show very conservative burst pressures, between 3.17 x and 5.19 MPa, for the four samples.

B31.G modified standard

The B31.G modified standard is an enhancement of the original B31.G method for assessing the remaining strength of corroded pipelines. The modified version refines the original approach by providing a more accurate and less conservative estimate of the pipeline’s remaining strength, particularly when dealing with deeper or more extensive corrosion.

It allows for more precise calculations by:

• Considering the actual profile and dimensions of the corrosion defect in greater detail.
• Reducing the level of conservatism in calculating the safe operating pressure of a corroded pipeline, leading to less unnecessary downtime or repairs.

One key improvement in the B31.G modified method is the use of the actual measured dimensions of the corroded area instead of idealised defect shapes. It also better accounts for longer, shallower corrosion profiles, which are less critical than deeper, smaller defects.

The B31.G modified standard is also integrated into VXintegrity’s Pipeline module.

The results obtained with the B31.G modified standard show slightly less conservative burst pressures, between 4.22 MPa and 6.68 MPa, for the four samples.

B31.G standard – effective area

While B31.G and its modified version focus on relatively simple and conservative assessments, B31.G Effective Area is an iterative method that adds a layer of sophistication. It provides a more accurate evaluation of corroded areas and a less conservative estimate of the corrosion profile by using a more detailed representation of the defect geometry. By using different lengths to approximate the corrosion profile and assessing more data points at high resolution, VXintegrity produces a more reliable and consistent assessment.

The data obtained with B31.G – Effective Area shows slightly more permissive burst pressures, between 5.11 MPa and 7.98 MPa, for the four samples.

PSQR

The Pipeline Stress and Qualification Review (PSQR) method is an approximation technique developed by TransCanada for calculating the burst pressure of pipelines, especially those with complexities not adequately addressed by other methods. It is designed to provide a more accurate and less conservative approach than traditional methods like B31.G. PSQR incorporates more nuanced considerations, allowing for a better balance between safety and efficiency.

The PSQR method is also integrated into VXintegrity’s Pipeline module. The results obtained with PSQR show less conservative and more accurate burst pressures, between 5.57 MPa and 8.85 MPa, for the four samples.

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Read the article online at: https://www.worldpipelines.com/special-reports/28022025/optimising-burst-pressure-rates/