1 mol% Oxygen exemption for the NTS

This study builds on previous technical work undertaken to support the 1 mol% oxygen Gas Safety Management Regulations (GSMR) amendment up to 38 barg. The work plan was targeted to focus on aspects that are more pertinent to the National Transmission System (NTS), including information from the current developments for European standards and supporting information from published studies on the impact of oxygen. The scope covered:

• Integrity – focusing on changes to corrosion rates and developing the understanding that increased oxygen content may have on the different factors that impact on corrosion rates.
• Measurement – considering the effect of higher oxygen content on the ability of the different analysers and equipment to measure accurately.
• Gas quality – reviewing the impact on key gas quality parameters and considering the potential impact on trace components that may be present.
• Pipeline “dryness” – investigating the impact of water dew point and water content and the effect of increased oxygen.
• Gas mixing – recognising that the flow from biomethane injection will in most cases be lower than the main pipeline flow, deduce if higher oxygen content gas could be transported long distances through the pipeline network.
• Gas storage – building on available information to assess if higher oxygen content impacts on gas storage.
• Gas utilisation – identifying if there are end users that could be significantly impacted by elevated oxygen limits.
• Intermediate limits – considering if an intermediate limit would be preferential.

The scope was developed to provide technical evidence to understand the implications for the NTS recognising that this introduces additional factors that were not considered in the previous studies.