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DNV GL © 2013 2015.01.21 SAFER, SMARTER, GREENERDNV GL © 2013
2020.12.02
Bjørn-Andreas Hugaas
Vice President
OIL & GAS
Transportation of Hydrogen Gas in Existing Carbon Steel Pipelines
DNV GL © 2013 2015.01.212
Introduction
DNV GL © 2013 2015.01.21
Hydrogen as an Energy Carrier
I will not spend time on:
the fact that hydrogen will play an important factor in
decarbonizing the world’s energy supply and building clean-
energy businesses, or
the three ways to produce H2 gas:
–GREY (out)
–BLUE (natural gas with CSS)
–GREEN (renewable sources)
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DNV GL © 2013 2015.01.21
Hydrogen as an Energy Carrier
Though, I will say something about how H2 gas may affect the material
properties and pipeline integrity.
In this regard it is important to ensure that our codes and standards have design
and material requirements that do not compromise the pipeline integrity (e.g.
DNVGL-ST-F101 and ASME B31.12).
If the understanding on how H2 gas affects the material properties is lacking;
Too conservative design and material requirements
However, by performing more testing to enhance our general understanding on
how H2 gas affects the material properties;
Less conservative design and material requirements
Possibly higher pressure and flow capacity
Better utilization of the pipeline system
Better economy
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DNV GL © 2013 2015.01.21
Safe H2 Gas Transportation
Identify the key issues that need to be considered to determine if a certain pipeline system can be safely used for H2 gas transportation.
Tailor make a qualification program addressing the key identified concerns.
If necessary, establish mitigation measures.
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DNV GL © 2013 2015.01.21
“The Overall Picture” for Carbon Steel Pipelines Exposed to H2 Gas
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Inside pipe Pipe wall Outside pipe
H2
+
Other“H
2>
2H
+”+
oth
er?
Crack nucleation
Crack growth/
Stability
H+
Diffusion
Coating
CP
SeawaterInhibitors?
Wett
ing
?
σ
pH2
DNV GL © 2013 2015.01.217
Key Materials Questions Related
to Hydrogen Embrittlement
DNV GL © 2013 2015.01.21
Key Materials Questions Related to HE
Is the environment and loading
scenarios likely to result in initiation of
hydrogen induced cracks from initially
defect free surface?
What are the conditions for an existing
crack to remain stable during constant
loading?
If comparing hydrogen charging by H2
gas and electrochemically, how will this
influence the likelihood to trigger HE?
8
?
Load
Crack extension
?
DNV GL © 2013 2015.01.219
Hydrogen uptake and transport and
Hydrogen Embrittlement Mechanisms
DNV GL © 2013 2015.01.21
Uptake and Transport of Hydrogen Gas
During transportation of H2 the following may happen:
- Adsorption: H2 gas will attach to the steel surface
- Dissociation: H2 gas will be separated into atomic H
- Absorption: H will migrate into the steel
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DNV GL © 2013 2015.01.21
Hydrogen Embrittlement (HE) - General
The first notable attempt at explaining HE was made by W.H. Johnson in 1874 and HE has since been a hot topic for researchers worldwide.
Despite the tremendous effort that has taken place to grasp the HE failure mechanisms, there are still several controversial findings.
No apparent single dominant mechanism.
Further work is required to fully understand these mechanisms at an atomic level.
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DNV GL © 2013 2015.01.21
Hydrogen Embrittlement - General
The three general prerequisites that need to be present to promote HE in metallic materials are:
A material that is susceptible to HE
Presence of nascent hydrogen
A sufficiently high stress level
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DNV GL © 2013 2015.01.21
Proposed Mechanisms of HE
Hydrogen Enhanced Localized Plasticity – HELP
Hydrogen Enhanced Decohesion – HEDE
Hydrogen Induced Pressure Cracking – HIPC
Hydrogen Enhanced Stress Induced Voids – HESIV
Adsorption Induced Dislocation Emission – AIDE
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DNV GL © 2013 2015.01.2114
Effect of Hydrogen on Material
Properties and Pipeline Integrity
FACTS
DNV GL © 2013 2015.01.21
Effect of Hydrogen on Material Properties and Pipeline Integrity
Depending on the H2 gas pressure and applied strain level, hydrogen will typically reduce the material’s fracture toughness and ductility.
The fatigue crack growth rate (FCGR) tends to increase with increasing H2 gas pressure and stress level (loading) – i.e. reduced fatigue life.
Hydrogen has limited effect the yield stress and tensile strength.
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DNV GL © 2013 2015.01.21
Effect of Hydrogen on Material Properties and Pipeline Integrity
For high stress levels, the
FCGR has been reported to
be 30-40 times higher for
pipeline steel exposed to H2
gas compared to air (fatigue
degradation).
Fatigue testing (X70)
indicates that weld metal and
HAZ exhibit similar FCGR as
for the base material when
exposed to hydrogen gas
(5.5 and 34MPa).
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DNV GL © 2013 2015.01.2117
Mechanism that may Reduce
the Effect of H2
DNV GL © 2013 2015.01.21
Addition of Oxygen may Inhibit H2 Dissociation
There are some studies indicating that addition of oxygen to the H2 gas
may inhibit the H2 dissociation process.
O2 has greater affinity to the steel surface compared to H2, and hence tend
to occupy the most favorable adsorption sites.
This will hinder the H2 adsorption and dissociation rates, and the
concentration of atomic hydrogen available to enter the steel reduced.
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DNV GL © 2013 2015.01.2119
Design code ASME B31.12 (2019)
- Hydrogen Piping and Pipelines
DNV GL © 2013 2015.01.21
Design code ASME B31.12 (2019) - Hydrogen Piping and Pipelines
ASME B31.12 is originally developed for onshore applications with focus
on structural strength and burst.
The updated 2019 version of ASME B31.12 is based on fatigue testing
only, which is justified by a statement that fatigue is the primary failure
mechanism in onshore pipelines.
A model for hydrogen-assisted fatigue crack growth of pipeline steel has
been included.
It is important to identify additional development work required to
maintain the same safety level as in the existing offshore pipeline design
code DNVGL-ST-F101.
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DNV GL © 2013 2015.01.21
Design code ASME B31.12 (2019) - Hydrogen Piping and Pipelines
Two possible approaches for material assessment:
–Option A (prescriptive design method): Based on a
material Hf performance factor, provides the reduction in
pressure for most common pipeline steel grades. Does not
require testing in hydrogen gas.
–Option B (performance-based design method): The
material performance is based on testing and not a “knock-
down” factor.
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DNV GL © 2013 2015.01.21
Current limitations with ASME B31.12
Axial loading not covered (e.g. girth welds).
No additional requirements for hoop stresses below 40% SMYS.
Addresses loading due to pressure in hoop direction only, e.g. no
requirements to ensure adequate fracture arrest properties.
Fatigue only from hoop stress variations.
Uncertainties related to weld performance.
Environmental loads not directly addressed.
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DNV GL © 2013 2015.01.21
RP for Hydrogen Transport
The current information in ASME B31.12; 2019 is not necessarily sufficient
to decide with a high level of confidence if a pipeline system is fit for
transportation of H2 gas or not.
DNV GL is planning a Recommended Practice to complement DNVGL-ST-
F101 for design of offshore hydrogen pipelines.
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DNV GL © 2013 2015.01.2124
Summary
Relevant Questions that Need to be Addressed
to Establish Non-Conservative Design Criteria
For H2 Gas Transportation
DNV GL © 2013 2015.01.21
Relevant Questions when it comes to HE
Will surface cracks be nucleated under normal operating conditions?
Will significant crack growth take place under constant loading?
How will the environment affect the resistance to crack initiation and
growth under cyclic loading?
Is H2 gas a concern for large-scale yielding failure modes as third-party
damage (e.g. anchor drag)?
Currently design decisions must be based on what is judged to
be representative test results – i.e. may be overly conservative.
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DNV GL © 2013 2015.01.21
SAFER, SMARTER, GREENER
www.dnvgl.com
QUESTIONS?
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