Specialist Consultancy in Cathodic Protection

 

Amtec consultants are specialist experts in cathodic protection issues concerning protecting painted & coated marine structures & ships with sacrificial anodes or Impressed Current Cathodic Protection ,ICCP, systems. This expert knowledge is also applicable to land based structures such as stainless steel tanks & pipe work where extremely low rates of metal loss is needed such as exists in the food processing & pharmaceutical industries. Often pitting or crevice corrosion are a problem. Failures & problems resulting from pitting, weld corrosion & crevice attack can be controlled by a well designed cathodic protection system.

Telephone & e-mail enquiries are initially free & confidential. Tel +44 1928 734996. E-Mail enquiries@amteccorrosion.co.uk

Sacrificial Anodes.

Modern coatings are not immune to the effects of cathodic protection. Too many anodes can cause premature coating degradation, paint failure & coatings which delaminate by a process called cathodic disbonding. The number, type and placement of anodes has to be carefully matched to the barrier properties of the coating, which will change with time. Magnesium anodes have a high output voltage in comparison to zinc anodes or aluminium anodes & special care should be taken when used in conjunction with anti corrosive coatings. The placement of aluminium anodes in ship's ballast tanks is regulated by classification society rules.The placement of anodes in ballast tanks can have serious effects on the overall coating life time.

Impressed Current Cathodic Protection.

I.C.C.P. systems need a similar degree of management - especially with irregularly shaped structures such as exist around the propellers , rudders & propulsion systems of vessels. This is particularly true of long vessels such as VLCC or ULCC tankers . Fast craft such as container ships or fast ferries have special needs with the placement of anodes or he design of impressed current, ICCP ,systems. Aluminium hulled vessels such as patrol craft, high speed catamarans, high speed ferries & super yachts have a large variation of current demand with speed & care needs to be taken with the design of the cathodic protection system & how it interacts with the coating system on the hull. The wrong combination of coating & cathodic protection system can result in either a poor economic situation or a poor service lifetime before serious maintenance cost are incurred.

ICCP System Malfunctions.

Often Impressed Current, ICCP, systems malfunction and cause damage to both the coating system & the metal of the structure or hull. This damage can often penetrate into pipe work and cause damage at weak points in the coating such as flanges or welds. The distribution of any a.c. component of the current can be very non uniform & become focused on vulnerable areas. Reference electrodes or power supply components can fail in an unsafe mode. Amtec can carry out in water ICCP potential surveys using sensitive d.c & a.c. instrumentation which can detect problems associated with failures & problems with ICCP systems. We also offer an independent monitoring service of ICCP system logs where the data is correlated with the voyage data from the vessel.This allows early detection of problems. Data loggers can also be attached to the system where the data can be returned to the U. K. for analysis.

Over Protection from Cathodic Protection Systems.

Getting the potential correct with the application of both Impressed Current (ICCP) & Sacrificial anodes to coated Items is essential. Under protection leads to corrosion & metal loss whereas overprotection can lead to coating delamination or blistering due to cathodic disbonding. Different coating systems behave very differently in the presence of cathodic protection, some are totally unsuitable ( such as alkyds & oleo resinous paints) & others such as epoxies & polyurethane behave well as long as they are chosen correctly. Overprotection is particularly associated with ICCP systems.

Telephone & e-mail enquiries are initially free & confidential.Tel +44 1928 734996. E-Mail enquiries@amteccorrosion.co.uk

Anode Placement & Potential Distribution.

The placement of both sacrificial & inert (MMO or mixed metal oxide together with platinised Titanium) is essential to get a good potential distribution that ensures to no areas are either under or over protected. For existing structures and vessels potential surveys using a half cell (either zinc or silver/silver chloride reference electrodes) are essential to get good anode placement, Amtec can carry out such surveys or supply the reference cells & give advice on how to carry out such surveys. The placement of anodes in tanks to help a failing coating system is an Amtec speciality - contact our Help line.

Cathodic Protection & Aluminium Hulls.

Great Care has to be taken with applying all forms of cathodic protection to aluminium vessels such as fast ferries, military vessels & pleasure craft. The problem lies with the fact that aluminium is very sensitive to alkali the conditions that are produced at the cathodic site. Aluminium dissolves rapidly in both alkaline & acidic environments. Great care has to be taken so as not to generate high localised current densities & also to calculate the rate of removal of both anodic & cathodic reactants and also with the installation of any insulation or anode shield material around the anodes. Over protection in terms of voltage range should also be avoided. Under protection of aluminium can result in severe problems with pitting corrosion.

Extended Lifetimes.

Where extended vessel lifetimes between dry docking's are required , such as with FPSO's, Amtec can monitor the behavior of the external and internal cathodic protection systems & regulate them is such a way as to extend the coating lifetime by minimalising cathodic disbonding & the formation of calcareous deposits.

Telephone & e-mail enquiries are initially free & confidential. Tel +44 1928 734996. E-Mail enquiries@amteccorrosion.co.uk

 

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