The Need for Pressure De-rating Prior To In-Service Welding
Status:
Complete
Project Reference Number:
NIA_NGGT0015
START DATE:
END DATE:
Project summary
Funding mechanism:
  • Network Innovation Allowance
Expenditure:
£85,000
Third Party Collaborators:
  • BMT Fleet Technology Ltd
Summary
Documents
The expected design pressure was limited to 70 barG with a specified maximum yield stress (SMYS) of 72%. Now National Grid have pipelines that may operate up to 80% of SMYS and pressures for some pipelines have increased to a maximum of 94 barG. To quantify the current specified safety factors, additional analysis, using the latest modelling techniques, is required to ensure that the mechanistic behaviour of the welding of hot-tap connections is better quantified and incorporated in best practice.
Benefits
The programme will provide a better understanding of the mechanical behaviour of pipe sections under the circumstances of hot tap welding operations which will either:

  • Confirm the existing safety margins already specified in the relevant National Grid standard T/SP/P/9 are appropriate

  • Will provide supporting evidence to be incorporated in an updated T/SP/P/9 standard.