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Direct Electrical Heating of Subsea Pipelines
Martin Høyer-Hansen Supervisors Prof. Arne
Nysveen Dr. Jens Kr. Lervik
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Why is heating needed?
Wax or hydrate plugs may block the pipeline
Must be prohibited either by chemical treatment
or heating!
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Electrical heating of pipelines - Alternatives
Indirect heating
Inductive heating
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Electrical heating of pipelines Alternatives
cont.
Direct heating
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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DEH system layout
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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DEH circuit equivalent
Typically 50-70 of the applied current (Icable)
returns in the pipeline
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Challenges with the DEH systemI Grounding the
pipeline

• At the cable connection points there will be a
  current transfer zone before a stationary current
  distribution is obtained

Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Challenges with the DEH systemI Grounding the
pipeline
About 65 current in pipe
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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2D finite element method simulation
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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2D finite element method simulation
66 current in pipe
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Challenges with the DEH systemI Grounding the
pipeline

• The anodes function is to sacrifice themselves
  to protect the steel pipe from corrosion

Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Challenges with the DEH systemI Grounding the
pipeline

• A crack in the pipe insulation may result in
  leakage currents

AC corrosion?

• If jac gt 240A/m2 risk of corrosion is significant
• Do ac currents affect the anodic protection
  system?

Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Challenges with the DEH systemII Variation in mr

• Pipelines are several welded batches
• A sudden change in mr between 2 batches results
  in a change in impedance
• the current distribution changes!
• May lead to large current densities in the case
  of a insulation holiday near this point

Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Further work

• In theory, the current distribution can be
  calculated by superposition of the applied ac
  currents and galvanic dc currents

• This simplifies FEM calculation considerably, as
  a transient analysis no longer is needed

Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Further work

• In practice, is the dc current dependent on the
  ac current???
• ac currents may alter passivating films
• If so how can this be modelled?

Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Thank you!
Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines
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Overview of presentation

• Introduction
• The direct electrical heating system
• Challenges
• Further work

Martin Høyer-Hansen, Direct Electrical Heating of
Subsea Pipelines