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Explain cathodic protection for marine vessels
Level
5
Credits
6
Purpose
People credited with this unit standard are able to explain: the process of
metal corrosion on vessels; cathodic protection of vessels using sacrificial
anodes; cathodic protection of vessels using an impressed current system;
electrolysis, electrolytic and stray current corrosion; and the potential effects
and prevention of over-protection on aluminium alloy vessels.
Subfield
Boating Industries
Domain
Boatbuilding
Status
Registered
Status date
21 May 2010
Date version published
21 May 2010
Planned review date
31 December 2014
Entry information
Open.
Accreditation
Evaluation of documentation and visit by NZQA and
industry.
Standard setting body (SSB)
Boating Industry Training Organisation
Accreditation and Moderation Action Plan (AMAP) reference
0136
This AMAP can be accessed at http://www.nzqa.govt.nz/framework/search/index.do.
Special notes
1
Vessels are expected to be greater than 20m but less than 120m in length.
2
Definition
Corrosion – electrochemical action produced by dissimilar metals in contact with
each other and an electrolyte that produces a flow of electrons and an associated
current flow.
3
Relevant reference standards
ABYC E-2 – Cathodic Protection
This standard is a guide for the design, installation, and use of cathodic protection
systems on boats. This standard applies to the use of galvanic anodes and
impressed current systems if installed on a boat.
ABYC E-11 – AC and DC Electrical Systems on Boats.
© New Zealand Qualifications Authority 2010
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These standards are guides for the design, construction, and installation of
alternating current (AC) and direct current (DC) electrical systems on boats.
http://www.abycinc.org/standards/toc.cfm.
NOTE: The United States Coast Guard has promulgated mandatory requirements for
electrical systems in Code of Federal Regulations (CFR), Title 33, Chapter 1, Part
183, Boats and Associated Equipment. Refer to the CFR for current federal
requirements. http://www.gpoaccess.gov/CFR/.
These standards apply: to direct current (DC) electrical systems on boats that
operate at potentials of 50 volts or less and to boat alternating current (AC) electrical
systems operating at frequencies of 50 or 60 hertz and less than 300 volts including
shore powered systems up to the point of connection to the shore outlet and
including the shore power cable.
AS/NZS 3004.2:2008 Electrical installations – Marinas and recreational boats –
Recreational boats installations.
Elements and performance criteria
Element 1
Explain the process of metal corrosion on vessels.
Performance criteria
1.1
Electrochemical corrosion is explained in terms of all the conditions that are
required for it to occur.
Range
includes – the corrosion cell, requirement for physical contact of
metals.
1.2
Explanation includes the flow of electrons and current in terms of direction of
each.
1.3
Explanation includes the current flow between different metals in terms of
potential voltage difference.
1.4
Explanation includes the concept of anodic and cathodic sites on single metals
corroding without contact with other metals.
1.5
Explanation includes the concept of energy required to manufacture and
corrode metals in relation to the metal’s position on galvanic series.
1.6
The effects of the properties of electrolyte are explained in terms of resistance
to current flow.
Range
1.7
includes – salinity, oxygenation.
Unique attributes of aluminium alloys are explained in relation to their natural
corrosion protection.
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Element 2
Explain cathodic protection of vessels using sacrificial anodes.
Performance criteria
2.1
A sacrificial anode protection system is explained in terms of protected
components, type and placement of anodes, and electron and current flow.
2.2
Cathodic protection using sacrificial anodes is explained in terms of advantages
and disadvantages compared to impressed current systems.
2.3
Cathodic protection using sacrificial anodes is explained in terms of bonding
requirements.
Range
2.4
includes – shaft bonding.
Installation requirements for sacrificial anodes are explained in terms of the
anode attachment system and its resistance.
Element 3
Explain cathodic protection of vessels using an impressed current system.
Performance criteria
3.1
An impressed current protection system is explained in terms of protected
components and electron and current flow.
3.2
Cathodic protection using an impressed current system is explained in terms of
advantages and disadvantages compared to sacrificial anode systems.
3.3
The system components are identified and explained in terms of their functions
and installation requirements within the system.
Range
3.4
includes but is not limited to – anode, reference electrodes, shield,
control system.
Cathodic protection using an impressed current system is explained in terms of
bonding requirements.
Range
includes – shaft bonding.
Element 4
Explain electrolysis, electrolytic and stray current corrosion.
Performance criteria
4.1
Electrolysis corrosion is explained in terms of its difference from common
electrochemical corrosion processes.
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4.2
Electrolytic corrosion is explained in terms of its difference from common
electrochemical corrosion process.
4.3
Stray current corrosion is explained in terms of electrical fault paths and
prevention.
Element 5
Explain the potential effects and prevention of over protection on aluminium alloy vessels.
Performance criteria
5.1
The implications of over protection on aluminium alloy vessels are explained in
terms of ions and the reduction of the properties of the alloy.
5.2
The prevention of over protection on aluminium alloy vessels is described in
terms of techniques and measurement.
Please note
Providers must be accredited by NZQA, or an inter-institutional body with delegated
authority for quality assurance, before they can report credits from assessment against
unit standards or deliver courses of study leading to that assessment.
Industry Training Organisations must be accredited by NZQA before they can register
credits from assessment against unit standards.
Accredited providers and Industry Training Organisations assessing against unit standards
must engage with the moderation system that applies to those standards.
Accreditation requirements and an outline of the moderation system that applies to this
standard are outlined in the Accreditation and Moderation Action Plan (AMAP). The
AMAP also includes useful information about special requirements for organisations
wishing to develop education and training programmes, such as minimum qualifications for
tutors and assessors, and special resource requirements.
Comments on this unit standard
Please contact the Boating Industry Training Organisation training@bia.org.nz if you wish
to suggest changes to the content of this unit standard.
© New Zealand Qualifications Authority 2010