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Cathodic protection works by providing sufficient current to polarise the at risk steel so that the electrical potential drops so that it what is called in the ‘immune zone’ and will not corrode. Galvanic anodes do that due the naturally low potential of zinc in the electrolyte surrounding the zinc. Impressed current anodes do it by the applied current from the power source. In both cases a uniform spread of current over the steel surface in contact with concrete is organised by the anode layout. Galvanic anodes are consumed in the protection process and have a life limited by the mass of zinc. Impressed current anodes have very very low consumption of the active surface due to the special metals used. However they require a transformer/rectifier control system and wiring that makes them more complex and they have a higher maintenance requirement. Hence the most appropriate system will be project specific. Corrpre lead the world in the development of their zinc activation paste that coats the active zinc surface and hence their anodes can achieve high polarisation of the steel surface in contact with the concrete. The specific arrangement of anodes will depend on the project. Roll anodes could be inserted in the deck surface above each beam or into the soffit adjacent to each beam as shown in the sketch to the right. The number of anodes required to achieve a given life varies depending on the beam width (steel surface area). A 20-25 year design life is typically assumed for a repair. Alternatively Zinc Layer Anode (ZLA) could be applied as a strip between the beams or in the same fashion as the magnetite floor protection method above the beam. Roll Anodes can be used to protect the as shown in the figure to the right .

View looking up at slab

Zinc Layer Anode can also be used by applying it to the soffit between beams. As beams get further apart the ratio of steel surface to anode surface remains the same so the design life remain constant. As the beam width increases for the same beam spacing the area of steel to be protected increases but the zinc mass remains the same. Hence design life decreases with increasing beam width. If the design life is less than that required then 2 strips of ZLA can be applied between each beam and this will double the life. If the beam width exceeds 150mm it is preferable to protect the beam from both sides and if the beam spacing is over 51cm this will require the use of 2 strips of ZLA between each beam. Design lives in excess of 25 years can not be relied on.

View looking up at slab

Various of the impressed current systems could be used for protection on large projects or projects where a life in excess of 25 years is required. DurAnodes require only a 12mm diameter hole and are the most effective internal impressed current anode because of the various design features. However if aesthetics is not a high priority, and that’s like to be the case in this type of construction, then the lowest cost, fastest installation and lowest noise is likely to come from the Cassette system as it is applied by bolting to the concrete surface. The DurAnode system can also be applied to the top of the slab, even in trafficked areas, to protect the underlying beams and this may be an advantage. The anodes and wiring are located below the concrete surface so the system is largely invisible making it very attractive where aesthetics are concerned.

View looking up at slab

Corrosion Proof Water Tanks

Heritage Tanks provide premium residential and commercial water tanks that are built tuff and use excellent quality BlueScope steel and the toughest liners in Australia. Take a look at Heritage Water Tanks here.

Zinc Tape makes for quick and long lasting repairs of hand rails, ideal for apartment blocks and beach side hand rails, Zinc Tape can be applied with the metapress with ease. Simply prepare the surface area, then apply Zinc Tape using either the meta press or meta wrapper.

Surface Preparation

Where a corroding pipe line is to be protected there are two key elements. Firstly the steel must be protected from further exposure to external elements, and secondly the steel must be protected from any corrosion occurring below the protective layer. In old pipes this is a significant issue, as chlorides trapped in pits for example can lead to rapid failure using conventional coatings. That is why a very high level of surface preparation is essential with conventional coatings.

The normal blast clean requirements to get bright steel to the SA 2.5 level is to open and clean out all pits so that there is no corrosion locked in beneath the coating. Whist this is good practice when using ZincTape, it is not so critical as the ZincTape provides galvanic protection at any localised corrosion cells.

As with most types of coating, correct surface preparation is essential in achieving the optimum performance of the applied coating. Because of the many applications of ZincTape it is recognised that it would be impractical to use the same method of surface preparation for all types of substrate, therefore we have listed a number of methods of surface preparation, all of which are suitable for the various substrates in their particular operating conditions. Follow the link for a full list of surface preparation methods.

Application methods

ZincTape is very easy to apply to pipes, even when they are already in fixed in place. The main methods of application of ZincTape are:

    • Spiral-wrapping
    • Cigarette-wrapping

These methods are covered in detail on the ZincTape application methods page, which covers the metapress and the metawrapper, two tools custom designed for the application of ZincTape. SRCP can provide these tools, depending on the size of the job and your individual needs.

Tips

  • Tips for the application of ZincTape to pipes to provide cathodic protection to the steel.A ZincTape strip should cover each relevant weld seam without interruption, extending 20 mm on each side (90o) to the weld, prior to coating the substrate proper.
  • During application, the tape should be pulled constantly without deforming it.
  • Air voids can be removed by pricking the ZincTape with a Craft Knife and rubbing with a wooden or hard-plastic spatula to ensure a good bond throughout.
  • Where ZincTape is applied to irregular shaped or previously corroded and pitted steel the use of a rubber mallet is also effective in ensuring good adhesion on pitted or irregular shaped areas.

Steelwork applications for Zinc Tape with conductive adhesive for active corrosion protection

Below you will find a brief review of Zinc Tape application methods, with links to a detailed background of how to apply them to various structures. For Zinc Tape application methods check out the Zinc Tape applications methods page. For surface preparation methods click here.

 Columns

Zinc Tape can be applied using the meta press or meta wrapper to street light poles as is demonstrated on the following page. Suitable for protecting all steel elements from corrosion, Zinc Tape can be used on any steel columns to great effect.

Contractors are often asked to install corrosion protection to steel columns of various lengths and shapes, often on site where Zinc Tape offers the perfect solution. For a decorative finish, any coating that would ordinarily be applied to HDG can be used in the same manner.

 Handrails

Often handrails can become subject to corrosion, particularly when near coastal areas. In many cases, handrails are hot dip galvanised prior to being installed, however, Zinc Tape offers better protection that hot dip galvanising, and can also be applied to areas that may need additional protection.

By using Zinc Tape, it is possible to achieve excellent quality repairs where corrosion may take place around joints or unprotected areas. This section of the web shows how Zinc Tape was applied to repair corrosion of a hot dip galvanised handrail in a coastal area.

 Pipes

The conductive adhesive is a vital part of ZincTape. There is a major difference in performance when the adhesive is conductive as it means the steel also has active corrosion protection.

The fastest and most efficient method of applying ZincTape to pipe structures is using a manually operated wrapping machine called a metawrapper, designed and developed to apply ZincTape onto just about any tubular surface. Metawrappers are available from SRCP to hire or purchase.

 Tanks

Tanks showing signs of damage in the form of corrosion can be repaired using ZincTape, with the conductive adhesive and application via the Magnetic Roller applicator making ZincTape applications easy and effective. Cut the tape to form at the irregular shapes first and thereafter the more uniform shapes.The tape should then be carefully applied ensuring no voids or creases. Water tanks can benefit from Australian water tank manufacturer Heritage Tanks.

 Beams

Penetration of chlorides or carbon dioxide at the interface between steel and concrete makes the top surface of steelwork and stud connectors susceptible to corrosion. As the steel work coating system deteriorates it will be repaired but there is no way of coating the tops of the beams or studs. Of particular concern are the points where the studs are welded to the beam as the original corrosion resistance here may have been weak. Corrosion product that forms on the top of the beam exerts tremendous force on the concrete above forcing it upwards and causing cracking. Protecting the top of the beam and studs is relatively easy using standard cathode protection systems for reinforced concrete. An anode system can be installed alongside the beam and it will protect all steel surfaces in contact with the beam. The use of impressed current or galvanic systems will depend on the project as both types of system are suitable. Galvanic will generally be most suitable where a low cost installation is required and a short design life (less than or equal to 25 years) is acceptable. Impressed current systems are likely to be favourable for long life and large scale projects.

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