Articles protection afforded by the coating system, increases the structure design life, and prevents deterioration of the structure. Cathodic Protection therefore prevents there being any loss of product caused by external corrosion, a v o i d i n g environmental damage and safety implications.
cathodic protection. •
Maintenance
Cathodic protection is an electrical system that will need regular inspection & maintenance by suitably qualified personnel (see Section 8.0) •
Design
Each petrol filling station will have different safety and cathodic protection design considerations that should be assessed by a competent individual.
Frequently Asked Questions: •
Permanent
CP Anode ready to be inserted
To guarantee freedom from corrosion the coating must completely separate the metal surface from the ground water (or electrolyte). Coatings alone cannot entirely eliminate corrosion, because they can never, in practice, be applied and buried without any defect or damage. However, a correctly designed and maintained cathodic protection system can guarantee to stop corrosion at a fraction of the cost for replacement system. •
Well Established
The application of cathodic protection to prevent external corrosion on new buried steel storage tanks is a well-established technique. It is routinely specified as a method of protecting thousands of LPG vessels in the UK, it is widely used in the US and in some EU countries it is mandatory to protect buried petrol storage tanks with cathodic protection. Cathodic protection has been accepted in the US by the Environment Protection Agency as a method to prove that underground storage tanks remain structurally sound, as required by Federal Law. •
Verifiable
Buried storage tanks cannot be easily inspected once they are buried, but when fitted with cathodic protection they can be monitored, to assess the tank's corrosion status and the level of cathodic protection applied. So what are the limitations on using CP? •
Evaluation
Not all buried storage tanks are suitable for upgrading by cathodic protection. Tests on the t a n k s condition should be carried out prior to the application of CP Test Fink
Q. Is it safe? A. Yes - it uses very low voltage/current and installation techniques are regulated by established industry codes. Q. Is it proven? A. The principles were established by Sir Humphrey Davy in 1820's. Routinely used on pipelines and used on underground LPG vessels it is well established. Tanks protected by CP are given same status as new tanks by US Environmental Protection Agency. Q. Is it economical to install? A. Typically 1/10 cost of replacement and only 2% of new tank installation. Q. What are the running costs? A. Typical power consumption equates to one light bulb. Annual Monitoring/Maintenance is quick, simple and cheap. Q. How long do these sacrificial anodes last? A. Ground conditions determine the amount of sacrificial anode material required and this would be decided at the design stage. The life of the anodes will be dictated by the output, which relates to the coating condition of the tank. Typically sacrificial anodes will have a life of 10 15 years. Replacement is normally possible with minimal disruption utilising a small drilling rig. Q. Can an operator save money by checking the anodes themselves? A. Specialists should be used to monitor cathodic protection systems. The checks are carried out annually, they are inexpensive (typically less than 20% of a precision tank test) and do not affect site operation. For more information please contact the author: Martin McTague of Ecotech on 01325 316081.
43
