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minimum required specific gravity (Picture 6).
Hydrogen Pipelines Offshore
As far as the occurrence of cyclic loads for offshore
The offshore pipeline Oil and Gas industry designed pipelines, the high longitudinal stress and strain due to
using a stress-based approaches till the 90’s when a the installation phase (Picture 7), to the sea bottom
dedicated R&D project - SUPERB JIP - introduced in unevenness and to the environmental loads need to be
DNV-ST-F101 (former DNV ’96) the “limit state” design verified against the impact of the presence of Hydrogen
approach. Since then, the design by failure mode is the on the resistance of pipe materials and welds to
basis for the offshore pipeline design and relevant fatigue.
safety factors are calibrated through structural reliability Fatigue damage is accumulated since the installation
theory based on acceptable target failure rates. The phase because of weather condition and depending
transportation of H , or H /NG through existing or on on dynamic response of the pipe-vessel system. Also,
2 2
purpose designed pipelines can cause additional the fatigue in operating conditions is caused by
failure modes or important changes on the failure environmental loads originating bending stress cycles
modes mechanisms with respect to the typical with frequencies of the order of less than one hertz
occurring to submarine pipelines according to DNV- joined with long cycles temperature and pressure
ST-F101. It is, therefore, required that a combined variations.
assessment is done, and cross correlation(s)
established among failure modes, material properties,
usual and typical loads of the new energy scenarios
and the specific fluid (e.g. H or H /NG) environment
2 2
(Torselletti et al., OMC-2021).
Hydrogen presents some unique “degradation
mechanisms” to be considered during design. It has an
interaction with typical offshore high strength line pipe
materials (e.g. API 5L X60, X65, X70) and pipe welds,
affecting key properties such as ductility, toughness
and fatigue performance. A dedicated Saipem Offshore
Engineering Team analyzed these issues considering all
typical failure modes applicable to an offshore pipeline.
Analysing the different failure modes, the one related to
circumferential stress is ruling the sizing of the offshore Picture 7 – Complexity of interactions pipe vessel
pipelines in shallow and medium water depth (up to and sea environment in different pipe laying
approx. 800 m, ASME B31.12 Option A) while in deep modes
or very deep water (above 800 m and up to 2000 m)
the wall thickness sizing is determined to fulfil the In fact, an important reference code such as ASME
criteria of collapse for external pressure, or the B31.12 2019 does not include a specific approach for
offshore pipelines or and for their girth welds that are
part of the offshore pipeline fabrication process
(Picture 8).

Based on these considerations it was decided to go
through steps starting from the analysis of how
hydrogen affects failure modes, elaborating a test
matrix for materials and welds in hydrogen environment
to consolidate or cover areas of uncertainties and work
on a methodology for qualification of new and existing
offshore pipelines to be re-purposed.
The years 2021-2022 have seen the dedicated Saipem
Offshore Engineering Team promoting first and then
joining in the JIP H2Pipe (started with 5 industry
participants, it reached more than 30) by DNV to write
a Guideline on design, construction and operation of
hydrogen pipelines (offshore steel pipelines) to
Picture 6 – Example of Sizing Criteria applicable to hydrogen offshore pipeline supplement the standard DNV-ST-F101 on submarine
design as a function of water depth pipeline systems. JIPH2Pipe is developing not only a

IndustrIal Plants - May 2023
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