The UKOPA Girth Weld Defect Database plays a critical role in assessing the integrity and reliability of pipelines across the UK’s Local Transmission System (LTS) and National Transmission System (NTS).
Here we delve into the findings from a recent in-depth analysis of the database, highlighting key insights and providing recommendations on how good quality and quantity of data is key to improving the management of pipeline girth welds – especially considering potential repurposing for hydrogen transport.
Background
Pipelines are the lifeline of energy distribution, and their safety is paramount. However, the integrity of girth welds — circumferential welds connecting pipe sections — can be a concern, particularly for pipelines constructed before the introduction of stringent welding standards in the early 1970s. These welds, especially those classified under the P/18 definition, often require careful inspection and management to ensure continued service without failure, especially during excavations.
The P/18 designation refers to pipelines built before 1972, with a diameter greater than 100 mm and a maximum operating pressure (MOP) exceeding 7 barg. The integrity of these older welds is crucial, particularly as the energy sector explores the possibility of repurposing natural gas pipelines for hydrogen transportation. Hydrogen embrittlement, a process where hydrogen can reduce the material fracture toughness and make it more prone to cracking failure, is a significant concern for these legacy systems.
Hydrogen Embrittlement: A Growing Concern
The potential for hydrogen embrittlement in girth welds presents new challenges. Hydrogen can reduce fracture toughness by half and significantly increase the fatigue crack growth rate, particularly in high-pressure environments. This makes understanding the existing defect populations and their sizes more important than ever, as the critical defect size decreases in a hydrogen environment. The UKOPA Girth Weld Defect Database provides a wealth of information that can help mitigate these risks, but the quality and completeness of the data is paramount.
UKOPA Girth Weld Defect Database: Key Findings
The UKOPA Girth Weld Defect Database is a valuable resource that documents faults and defects in pipeline girth welds from 1962 to 2020. The analysis revealed several important trends and data quality issues:
- Distribution of Defects: Most girth weld defects discovered were relatively small, with lengths under 50 mm. However, there were a notable number of fully circumferential defects, which are more concerning due to their potential to cause leaks. This assumed that the designation of length referred to the circumferential extent of the defect.
- Data Quality Challenges: The database contains numerous entries with missing or unclear data. For instance, defect dimensions were often not well-defined, and in some cases, data entries included anomalies such as defect depths greater than the wall thickness. Only 25% of identified defects had defect depth readings recorded. These issues necessitate assumptions and adjustments, which can impact the accuracy of the analysis.
- Historical Data Limitations: Correlating defects with the age of the pipeline proved difficult due to incomplete records. Additionally, early data entries, particularly from the 1960s and 1970s, often lack the rigour of later records, making trend analysis challenging.
- Statistical Analysis: Despite these challenges, the analysis provided valuable insights into defect distributions across different parameters, such as operating pressure, pipe diameter, and material grade. These insights are crucial for prioritising inspection and maintenance efforts, especially for pipelines at higher risk of hydrogen embrittlement.
Recommendations
Based on the findings from the UKOPA Girth Weld Defect Database analysis, several recommendations have been made to improve data quality and pipeline safety:
- Enhance Data Collection: Gas Networks (GNs) should improve the completeness and accuracy of data submitted to the database. This includes ensuring that defect dimensions—length, width, and depth—are clearly defined and recorded.
- Standardise Reporting: Implementing standardised guidelines for recording and reporting defect data will help ensure consistency across different GNs and over time.
- Focus on Pipeline Age Data: Improving the availability and accuracy of pipeline age data will enhance the ability to correlate defects with the pipeline’s construction period, which is critical for assessing risk.
- Prepare for Hydrogen: Given the challenges posed by hydrogen embrittlement, there is a pressing need to gather more detailed information on defect sizes and material properties in pipelines that might be repurposed for hydrogen transport.
The UKOPA Girth Weld Defect Database provides a crucial foundation for understanding and managing the risks associated with pipeline girth welds. However, the analysis highlights significant areas for improvement in data quality and reporting standards.
Future needs for the gas industry with new fuels such as hydrogen will require better quality and greater quantity of data. This needs to be incorporated into current business practices. For example, when an excavation and repair is made on a pipeline, it is cost-effective to make the small additional effort and incur the minor cost of collecting precise data on the defect being repaired.
The safety cases for repurposing of the gas network for methane/hydrogen blends requires several integrity assessment steps to be taken. These will rely on collecting specific data about the condition of the assets. Some of the data required is not currently routinely collected. For the gas industry to help meet net zero targets by 2050, a different approach to data collection and analysis is needed.
UKOPA’s Failure and Risk Assessment Working Group is working to identify and address these issues so the industry can better ensure the safety and integrity of the UK’s pipeline infrastructure, particularly as it adapts to new challenges like hydrogen transportation.