Learnings

Outcomes

The TDW stopple (as used by NGS) is not designed to be operated as a single isolation seal and is normally used in conjunction with another stopple. The technicians who performed the stopple operation were open about the levels of let-by they would expect to operate in under methane conditions. Acceptable let-by levels were not quantified and were not documented across existing NGS procedures, this demonstration was to establish if the stopple did isolate hydrogen (or substitute medium). 

As is described the seal did not provide a 100% seal on helinite or on 100% nitrogen condition. The pressure drops observed do not appear consistent across the two test gases, which would affirm that the sealing face is not suitable for repeated sealing in one deployment, even without retraction. This was highlighted by the technicians as a concern during the demonstration. 

The stopple housing itself held pressure with no pressure drop, therefor demonstrating no leak path and proving it was completely effective at holding helinite, which determines it should hold hydrogen safely for future operations.

The existing practices and procedures used do not appear to have any gaps for deployment in hydrogen environments.  However, the consideration when deployed in hydrogen provisionally was to extend the hold and test periods. This consideration however was communicated on site and was not provided in written procedures. 

Lessons Learnt

The aim of the project was to successfully demonstrate the suitability of the Stopple tool in hydrogen operations. This project proved that on its own and in the set up tested, it would provide an ineffective seal in a hydrogen pipeline.  Further investigation is needed to understand the effectiveness of double deployment (Stopple Train), where the Stopple would be used in conjunction with additional seals. 

This demonstration of the operational effectiveness of the stoppling operation is in essence a demonstration of business as normal approaches to understand any observed gaps or improvements for potential hydrogen operations.

This project provided critical insight into the identified issues and illustrated solutions for the commissioning to 100% hydrogen for the wider gas transmission network. Lessons learnt from this project will be disseminated to the other gas distribution networks through the appropriate channels.