Joint Industry Project

Developing a unified guideline for the design and operation of rigid spools

Addressing the need for a unified guideline

The offshore industry continues to evolve, demanding robust and reliable solutions for subsea pipeline systems. Rigid spools are critical components, connecting pipelines and subsea structures. However, the current absence of explicit, industry-wide guidance for their design and operation presents challenges to ensuring safety, efficiency, and consistency across projects. To address this gap, DNV is launching a new Joint Industry Project (JIP) to develop a comprehensive guideline for the design and operation of rigid spools.

Background

The industry standard, DNV-ST-F101 (December 2021), offers limited coverage on rigid spool design, particularly lacking explicit limit state criteria for spool bends. This gap leads to varied interpretations, inconsistent practices, and potential safety risks or over conservatism. Meanwhile, Equinor has together with DNV developed and successfully implemented an internal rigid spool design guideline, setting a benchmark for best practices. Its adoption has delivered tangible improvements in reliability and constructability, demonstrating the value of a structured approach, assuring compliance to industry standards while optimizing the design. Equinor has kindly offered to release this guideline as basis for the JIP.

Objectives

The primary objective of this JIP is to create a unified and practical guideline that addresses the current shortcomings in rigid spool design and operation. By building on Equinor’s proven methodology and expanding it through industry collaboration, the project aims to:

  • Define clear, explicit limit state criteria for spool bends
  • Standardize design and operational procedures for rigid spools across the industry
  • Enhance safety, reliability, and constructability in spool applications
  • Lay the foundation for a future DNV Recommended Practice, recognized by operators, manufacturers, contractors, and authorities.

Scope of work

To ensure a comprehensive and effective outcome, the JIP will be structured into the following work packages:

  • WP1: Gap analysis, industry survey and define focus areas
  • WP2: Execute and document selected focus areas
  • WP3: Develop new industry guideline

Key focus areas

The JIP will focus on addressing critical technical and operational topics, including:

  • Explicit limit state criteria for spool bends and interfaces
  • Design methodologies for various spool geometries and materials
  • Fabrication, installation, and operational considerations
  • Inspection, testing, and maintenance requirements
  • Alignment with regulatory frameworks and industry standards.

Active engagement and input from operators, steel manufacturers, EPCI-contractors, and authorities will be essential to ensure the guideline is robust, practical, and widely accepted.
Currently, the following areas for further development are suggested and are listed here for inspiration:

  • Improved guidance on in-plane vs. out-of-plane behaviour
  • Optimization of conservatism levels in out-of-plane bending assessments
  • Expansion of the range of steel material grades covered in the guideline
  • Reassessment of flexibility factors, comparing with elbow elements, with the aim of enabling the use of elbow elements
  • Slug load considerations in spool design

Expected outcomes

Upon completion, the JIP will deliver a unified guideline for the design and operation of rigid spools, addressing the current gaps and harmonizing practices across the sector. This guideline will serve as the basis for a future DNV Recommended Practice, supporting safer and more efficient subsea developments worldwide. The collaborative nature of the project ensures that the resulting guidance reflects the collective expertise and needs of the industry.

Join the initiative

We invite operators, steel manufacturers, EPCI-contractors, engineering consultant and regulatory authorities to participate in this important Joint Industry Project. Your expertise and collaboration are vital to shaping a unified guideline that will elevate industry standards and ensure the continued success of offshore projects. For more information on how to join, please contact DNV’s JIP coordination team.

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