Technical Presentations at the October 2006 Meeting

2.1   Low Signature Impressed Current Cathodic Protection Systems - Recent Developments - Future Concepts’, Barry Torrance (Aish Technologies Limited)  

After a brief introduction to present Impressed Current Cathodic Protection (ICCP) technology and its purpose in minimising corrosion, this paper reviewed recent developments in ICCP equipment and its contribution to (a) hull condition management, and (b) corrosion-related signature management.   

It also looked forward to some future concepts. 

The topics are grouped broadly into ‘corrosion reduction’ and ‘signature reduction’ areas, but there is much interaction between the two.  This interaction can be managed with computer control. 

The paper emphasised the need for corrosion and signature management to be built into the design of a vessel right from the start, rather than being almost an afterthought. 

Topics covered:

Hull Condition Management

Corrosion-Related Signature Management

Equipment Overview

Computer Controlled Multi-Zone systems

Active bonding of moving parts

System Modelling

Condition Based Maintenance

Accuracy and Reliability of ICCP information

Fine-Grain ICCP

Damage location

High-Immunity Reference Electrodes

Own-Ship Signature Display

Diver-Safe ICCP 

(Similar paper previously presented at: ‘Underwater Defence Technology Europe’, Amsterdam, June 2005; ‘Recent Advances in Cathodic Protection’, University of Manchester, February 2006; NACE / CB&I John Brown Limited Evening Technical Meeting, May 2006)

2.2   Keynote Lecture:     Application of Physical Scale Modelling to the Evaluation of a ship’s ICCP Systems’, Horst-Friedrich Arendt (ex-Bundeswehr Technical Centre for Ships and Naval Weapons, Germany) 

The purpose of this fundamental study was to establish optimum cathodic corrosion protection system configurations for ship hulls. Comprehensive surveys were conducted in order to develop a better understanding of the electro-chemical processes occurring on a ship hull in a seawater electrolyte. The results obtained show that the performance of a system can only be evaluated when it is installed on a real object. However, once installed the location of the impressed current anodes and the reference electrodes cannot be changed if the potential distribution over the underwater hull is not optimal. Hence, a procedure had to be established that permits the development and optimisation of system configurations for future objects. 

A validated, experimental laboratory technique using scale ship models was established to determine the fundamentals of cathodic corrosion protection and to develop a theoretical understanding of the underlying mechanisms. The findings obtained in practice could be applied to the models. The model studies were conducted in a systematic manner and under defined conditions in German standard (DIN) artificial seawater and in a natural electrolyte. 

The experiments clearly showed the functional correlation between the geometric configuration of the reference electrodes on the hull and the locations of the anodes. The results reflect the interrelationships between the electro-chemically more positive bronze propeller and the steel. The configuration developed in the course of the experiments provided an optimum distribution of the protection current over the entire hull model. 

The data from the model study were applied to the design features of the Class 123 Frigate. Subsequently, the efficiency of this procedure was evaluated on a real object in a real electrolyte.

The results obtained clearly demonstrate that physical scale modelling is a rational, scientific method for the evaluation and design of impressed current cathodic protection systems.

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4.1   Long range guided wave inspection for oil pipelines and offshore risers’, Prof Peter Cawley (Imperial College, London) 

This presentation considered the attraction of guided waves for long range inspection and the problems to be overcome.  It then looked at examples of use: pipes in chemical plant, offshore and target applications and sensitivity. 

Typical Ranges (in each direction, using standard transducers) are as follows: 

·        In ideal conditions: 80m

·        Typical 30 year old pipe with little internal or external corrosion: 40m

·        Typical 30 year old pipe with some general corrosion: 20m

·        Typical pipe wrapped in factory applied foam:15m

·        Heavily corroded pipe or pipe that is bitumen wrapped: 5m

·        Six welds

·        The first flange or the second bend or branch

 Note: these ranges can be doubled by using low frequency transducers  

Target Applications are those requiring rapid, full coverage screening of pipes.  Especially cost effective in locations with difficult access, such as sleeved road crossings, corrosion under insulation, wall penetrations, pipe racks and rope access.  Can detect cracks and general metal loss (greater than 5% of the cross-sectional area). 

The conclusions were: 

·        Long range guided wave inspection now in routine commercial use worldwide

·        Particularly valuable for screening long lengths of pipe and for testing inaccessible areas

·        Increasing use offshore and new applications subsea

·        Dry coupled piezoelectric array very quick to attach and gives reliable, reproducible results with minimal surface preparation

·        Permanently attached arrays now available

           Measurement of mode conversion is a key feature for reliable feature recognition

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