Corrosion Protection for Offshore Pipelines

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Corrosion Protection for Offshore Pipelines

• Ernest W. Klechka, Jr., P.E.
• CC Technologies
• Dublin, Ohioeklechka_at_cctechnologies.com

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Methods for external protection of sub-sea
pipelines

• Design plays a big role in corrosion control
• Primary protection is provided by coatings
• Cathodic protection is used to protect holidays
  in the coating

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Internal Corrosion Control Requires Monitoring

• Chemical injection
• Corrosion inhibitors
• Biocides
• Scale inhibitors
• Materials selection
• 13-Cr alloys
• Duplex Stainless steels
• Not usually controlled with coating

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Corrosion Control Integrity Management Flow
Diagram
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Operating temperature has a great influence on
corrosion control

• Operating temperature can be as high as 65oC to
  100oC
• For every increase of 10oC the corrosion rate
  nearly doubles

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Design data needed for internal corrosion control

• CO2
• H2S
• Oxygen content
• Operating temperature and pressure
• Organic Acids, pH
• Velocity
• Solids, three phase flow,scaling

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Design data needed for external corrosion control

• Operating temperature
• Water temperature
• Water movement
• Depth of water
• Burial
• Pipe size and length

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External corrosion failure modes

• Seawater corrosion, scowering, abrasion of the
  coating, and sea bottom movement
• Galvanic corrosion (dissimilar metals in an
  electrolyte)
• Oxygen concentrations cell corrosion (pitting and
  crevice corrosion)

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Design Of Risers Effects The Choice Of Coating
Materials

• Riser can be coated
• Fusion Bond Epoxies
• Three layer systems
• Rubber linings
• Risers can have extra wall thickness for
  corrosion and mechanical damage allowance

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Typical Pipeline Coatings For Corrosion Control

• External pipeline protective coatings
• Fusion bond epoxy
• With a rough coat
• Polyethylene coatings (2 layer)
• Three layer
• Polyolefin coatings (3-layer PE and 3-layer PP)
• Bitumen, asphalt and coal tar coatings
• Coal tar epoxies
• Coal tar urethanes
• External concrete coatings
• weight coatings
• Polymer concrete

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Qualification requirements for fusion bonded
epoxy coatings
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Typical properties for extruded polyolefin
coatings
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Typical properties for coal tar enamel coatings
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Typical corrosion allowances for internal
corrosion of carbon steel subject to in service
corrosion.
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Cathodic Protection of Sub-sea Pipelines

• Impressed current cathodic protection (ICCP)
• Onshore
• Offshore
• Sacrificial cathodic protection
• Bracelet anodes
• Aluminum
• Zinc

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Cathodic protection design parameters and
coatings design considerations
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Typical calculation for anode bracelet design

• IReq IdesignApipeFCoating/1000 (1)
• Where
• IReq is the total current demand (Amps)
• Idesign is the design current density
• Apipe is the total area of the pipeline
• FCoating is the coating breakdown factor

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total anode weight required is then Wanodes
(Ireq 8760 hr/year expected life) /
(Consumption rate efficiency) (2) Where Wanod
es is the total anode weight need to provide the
current requirement Ireq is the required current
calculated in equation (1). anode
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The number of anodes then is calculated
as Ntotal Wanodes/ W bracelet (3) Where Ntota
l is the total number of bracelet anodes
requires Wanodes is the total weight calculated
in equation (2). W bracelet is the weight of each
individual bracelet
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Monitoring and Inspection of Coatings

• As part of the corrosion designs for offshore
  pipelines corrosion monitoring and corrosion
  inspection plans are needed.
• These plans are intended to monitor the
  effectiveness of corrosion mitigation and to
  measure changes as the pipeline ages.

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Determining the effectiveness of corrosion control

• Side scanning sonar
• detect areas where the pipeline may be bridging
  the ocean floor
• shifting of the ocean floor
• Cathodic protection monitoring
• potential survey
• current drain surveys.
• These surveys provide information about the
• condition of the cathodic protection system
• coating performance and coating breakdown.

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Inspection and testing can demonstrate pipeline
integrity

• In-line inspection tools
• Magnetic flux leakage
• Ultrasonic testing
• Hydrostatic testing
• Pressure testing
• Spike testing

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Coatings supplemented with cathodic protection
can result in long service life

• The first line of defense for an offshore
  pipeline is the coating on the pipe.
• Many different types of coating are used for
  offshore pipeline.
• Coatings for offshore must have good resistance
  to water absorption, cathodic disbondment, and
  strong adhesion to the pipe.
• Cathodic protection is used to protect holidays
  in the coating.
• Testing of coatings can provide some guidance
  concerning the ability of a coating to survive
  the offshore environment. Coating history and
  performance is very valuable information.

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Questions?Some Answer!