Methods for external protection of subsea 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
Internal Corrosion Control Requires Monitoring
- Chemical injection
- Corrosion inhibitors
- Biocides
- Scale inhibitors
- Materials selection
- 13-Cr alloys
- Duplex Stainless steels
- Not usually controlled with a coating
Corrosion Control – Integrity Management Flow Diagram
The operating temperature has a great influence on corrosion control. The operating temperature can be as high as 65oC to 100oC. Usually, for every increase of 10oC, the corrosion rate nearly doubles
Design data needed for internal corrosion control
- CO2
- H2S
- Oxygen content
- Operating temperature and pressure
- Organic Acids, pH
- Velocity
- Solids, three-phase flow, scaling
Design data needed for external corrosion control
- Operating temperature
- Water temperature
- Water movement
- Depth of water
- Burial
- Pipe size and length
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)
Design Of Risers Effects The Choice Of Coating Materials
- The riser can be coated
- Fusion Bond Epoxies
- Three-layer systems
- Rubber linings
- Risers can have extra wall thickness for corrosion and mechanical damage allowance
Typical Pipeline Coatings For Corrosion Control
- External pipeline protective coatings
- Fusion bond epoxy
- With a rough coat
- Polyethylene coatings (2 layers)
- 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
Qualification requirements for fusion bonded epoxy coatings
Typical properties for extruded polyolefin coatings
Typical properties for coal tar enamel coatings
Typical corrosion allowances for internal corrosion of carbon steel subject to in-service corrosion:
Cathodic Protection of Sub-sea Pipelines
- Impressed current cathodic protection (ICCP)
- Onshore
- Offshore
- Sacrificial cathodic protection
- Bracelet anodes
- Aluminum
- Zinc
Cathodic protection design parameters and coatings design considerations:
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.
Determining the effectiveness of corrosion control
- Side scanning sonar detects 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.
Inspection and testing can demonstrate pipeline integrity
In-line inspection tools
- Magnetic flux leakage
- Ultrasonic testing
Hydrostatic testing
- Pressure testing
- Spike testing
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 pipelines. Coatings for offshore must have good resistance to water absorption, cathodic dis-bonding, and strong adhesion to the pipe.
Cathodic protection is used to protect holidays in the coating.
The 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.
Online Video Courses related to Pipeline Engineering
If you wish to explore more about pipeline engineering, you can opt for the following video courses
- Pipeline Stress Analysis using Caesar II
- Design of Underground Pipeline Supports
- Hot Tapping in Piping and Pipeline Industry
- Buried or Underground Pipeline Stress Analysis using Caesar II
Few more Pipeline related useful Resources for You..
Underground Piping Stress Analysis Procedure using Caesar II
Comparison between Piping and Pipeline Engineering
A Presentation on Pipelines – Material Selection in Oil & Gas Industry
Corrosion Protection for Offshore Pipelines
Start up and Commissioning of the Pipeline: An Article
DESIGN OF CATHODIC PROTECTION FOR DUPLEX STAINLESS STEEL (DSS) PIPELINE
AN ARTICLE ON MICRO TUNNELING FOR PIPELINE INSTALLATION
A short presentation on: OFFSHORE PIPELINE SYSTEMS: Part 1
Factors Affecting Line Sizing of Piping or Pipeline Systems
Its very difficult to handle machinery ,equipment and pipelines which are located in offshore.This technology is amazing.Thanks for sharing such amazing and informative article which will help people to make the pipeline corrosion and rust free in the offshore are .