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
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 |
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 |
Corrosion Protection
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.