Introduction

External corrosion of subsea pipelines is the degradation of the metal by its electro-chemical reaction with the environment. The primary cause of external corrosion is due to an effect known as galvanic corrosion.

One method of protecting the pipeline is by using Cathodic Protection.

Galvanic corrosion occurs as all metals have different natural electrical potentials. When two metals have different potentials and are electrically connected via an electrolyte, current will flow from the more active (lower potential) metal to the other (higher potential), which will cause corrosion. The higher potential material is called the cathode, and the lower potentiual material is called the anode.

In the diagram, the more active material (Zinc) is the anode, and the less active material (steel) is the cathode.

The current passing through the electrolyte will cause the anode to dissolve as ions in the electrolyte.

The protection occurs as the cathode receives electrons from the anode via the metallic electrical connection. The result is that the cathode will be negatively polarised and thus protected against corrosion

buckling

Notable Projects

Project Name
Project Number
Notes
BAOBAB
Notable due to the Pipe in Pipe nature
Greater Plutonio
Deep Water, using SAFEBUCK
Qatar Gas
KW

Large Diameter Pipe
Shallow Water
Snake Lay Solution

 

Other Projects

Project Name
Project Number Notes
EPC2B
KW 0728
Controlled Buckles on Existing Pipeline Crossings
Algeria Pipeline
KW 1071
Onshore
Deep Panuke
 

 

Codes & Standards

Company
Title
Doc Number / Date
SAFEBUCK JIP
Safe Design of Pipelines with Lateral Buckling - Design Guideline
DNV
Global Buckling of Submarine Pipelines
DNV-RP-F110
DNV
Submarine Pipeline Systems
(Strain Based Limit State)
DNV-OS-F101

 

Course Notes

Author
Title
Notes
C. Sicilia
Lateral Buckling Assessment and Mitigation Design
Trevor Gee
IBC
Pipeline Course

 

Books

Author
Title
Chapter
Mikael Braestrup
Design and Installation of Marine Pipelines
6.5

 

Papers

Author
Title
Notes
Hobbes, R. E.
In-service Buckling of Heated Pipelines, Journal of transportation Engineering, ASCE, Vol. 110, No.2, March 1984, pp. 175-189
Approximate method for determining propensity for lateral buckling
Taylor, N. and Gan, A. B
Submarine pipeline Buckling – Imperfection Studies, Jour. Of Thin-walled Structures, Vol. 4, 1986, pp 295-323
A developed version of ‘Hobbs’, including the effects of initial OOS

 

Prepared Calculations

Title / Software
Description
Owner / Athor
Hobbs / Excel
Predicts the onset of buckling
KAJW / CSG

 

Related Subjects

Corrosion Assessment

Wall Thickness Assessment

Structures - Corrosion Protection

Corrosion Protection

Return

The Cathodic Protection system is normally combined with an External Coating System. The coating system is the primary barrier for protection, and reduces the requirement of the cathodic protection system by providing an electrical barrier between the cathode and electrolyte. Coatings that are used are primarily polymers or paint systems.