transportation of hydrogen gas in existing carbon steel

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

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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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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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“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

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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

?

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Hydrogen uptake and transport and

Hydrogen Embrittlement Mechanisms

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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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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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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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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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Effect of Hydrogen on Material

Properties and Pipeline Integrity

FACTS

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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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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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Mechanism that may Reduce

the Effect of H2

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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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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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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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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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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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Summary

Relevant Questions that Need to be Addressed

to Establish Non-Conservative Design Criteria

For H2 Gas Transportation

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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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transportation of hydrogen gas in existing carbon steel

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