cathodic_protection_in_practise(1) - CATHODIC PROTECTION P E FRANCIS CONTENTS 1 INTRODUCTION.2 2 PRINCIPLES OF CATHODIC PROTECTION.3 3 METHODS OF

cathodic_protection_in_practise(1) - CATHODIC PROTECTION P...

This preview shows page 1 - 4 out of 22 pages.

1 [CATHODIC PROTECTION/BM] CATHODIC PROTECTION P E FRANCIS CONTENTS 1 INTRODUCTION ............................................................................................................ 2 2 PRINCIPLES OF CATHODIC PROTECTION .......................................................... 3 3 METHODS OF APPLYING CATHODIC PROTECTION ........................................ 5 3.1 IMPRESSED CURRENT .......................................................................................... 5 3.2 SACRIFICIAL ANODES .......................................................................................... 6 4 DESIGN ............................................................................................................................ 8 4.1 PROTECTION POTENTIALS ................................................................................. 8 4.2 CURRENT DENSITY ............................................................................................... 8 4.3 COATINGS ............................................................................................................... 9 4.4 CALCAREOUS SCALES ......................................................................................... 9 4.5 CHOICE OF CATHODIC PROTECTION SYSTEM .............................................. 9 4.6 ANODE RESISTANCE .......................................................................................... 10 4.7 DANGERS TO BE AVOIDED ............................................................................... 12
Image of page 1
2 [CATHODIC PROTECTION/BM] CATHODIC PROTECTION P E FRANCIS 1 INTRODUCTION The first practical use of cathodic protection is generally credited to Sir Humphrey Davy in the 1 82 0s. Davy’s advice was sought by the Royal Navy in investigating the corrosion of copper sheeting used for cladding the hulls of naval vessels. Davy found that he could preserve copper in sea water by the attachment of small quantities of iron or zinc; the copper became, as Davy put it, “cathodically protected”. The most rapid development of cathodic-protection systems was made in the United States of America to meet the requirements of the rapidly expanding oil and natural gas industry which wanted to benefit from the advantages of using thin-walled steel pipes for underground transmission. For that purpose the method was well established in the United States in 1945. In the United Kingdom, where low-pressure thicker-walled cast-iron pipes were extensively used, very little cathodic protection was applied until the early 1950s. The increasing use of cathodic protection has arisen from the success of the method used from 1952 onwards to protect about 1000 miles of wartime fuel-line network that had been laid between 1940 and 1944. The method is now well established. Cathodic protection can, in principle, be applied to any metallic structure in contact with a bulk electrolyte. In practice its main use is to protect steel structures buried in soil or immersed in water. It cannot be used to prevent atmospheric corrosion. Structures commonly protected are the exterior surfaces of pipelines, ships’ hulls, jetties, foundation piling, steel sheet-piling, and offshore platforms. Cathodic protection is also used on the interior surfaces of water-storage tanks and water-circulating systems. However, since an external anode will seldom spread the protection for a distance of more than two or three pipe-diameters, the method is not suitable for the protection of small-bore pipework.
Image of page 2
3 [CATHODIC PROTECTION/BM] Cathodic protection has also been applied to steel embedded in concrete, to copper-based alloys in water systems, and, exceptionally, to lead-sheathed cables and to aluminium alloys, where cathodic potentials have to be very carefully controlled. 2 PRINCIPLES OF CATHODIC PROTECTION Corrosion in aqueous solutions proceeds by an electrochemical process, and anodic and cathodic electrochemical reactions must occur simultaneously. No nett overall charge builds up on the metal as a result of corrosion since the rate of the anodic and cathodic reactions are equal.
Image of page 3
Image of page 4

You've reached the end of your free preview.

Want to read all 22 pages?

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes