Archives for May 2013

Cold Shrink and Heat Shrink tubing may appear similar from the outside, but their key characteristics are very different. Both types of tubing have different installation techniques, applications and physical properties.

HeatShrink and ColdShrink tubing can be used for a variety of cabling applications including: terminating, splicing and providing environmental seals on LV and MV cables. More than price, ease of use and environmental conditions should be taken into consideration when choosing the most suitable product.

The differences

The most obvious differences between the two products are how each of them is applied. Cold Shrink comes stretched over a removable plastic core, allowing the tube to be slid over the application, the core removed and the tubing will contract to create a watertight-seal around the cable or connection due to the ‘active memory’ contained within the EPDM rubber or silicone material. Heat Shrink, also comes pre-stretched but as a sleeve rather than over a removable core. The sleeve requires a heat source for installation, usually from a gas torch, to heat the polyolefin tubing so that it shrinks to its original size, creating a seal over the cable or joint.

Silicone-rubber Cold Shrink tubing has the greater UV-resistance of all the types of cold or heat-applied tubing and is therefore used in outdoor, exposed environments, for example: trackside terminations to rail power lines. EPDM rubber is also used in Cold Shrink tubings and is much more abrasion resistant than other cold or heat-applied products, being ideally suited for direct burial applications such as cable-to-cable jointing.

Cold Shrink tubing has an “active memory” seal characteristic, meaning the tubing is always trying to return to its original size and able to maintain its sealing capability around cables as they expand and contract under large load-swings or temperature fluctuations.

Another advantage of Cold Shrink tubing is that, because there is no direct flame required to install components, there is a reduced risk to the installer, especially in the presence of combustible gasses. Hot-work permits are not required and quality and reliability of the installation is guaranteed due to fewer critical installation techniques, with resultant time and cost savings.

The polyolefin-based material used in Heat Shrink is resistant to most chemicals and also becomes very rigid once it has been heated, therefore making it a good choice for mechanical protection. However, the downside to this rigidity is the products inability to expand and contract with the cable, meaning an environmental seal cannot be maintained without the aid of hot-melt adhesives or mastic tapes. Heat Shrink materials are not suited for installation areas experiencing high heat or humidity, but are ideal for use in most industrial/commercial installations where operating temperatures are below 90o^C and where chemical resistance is required.

Video: ColdShrink Joint vs HeatShrink Joint

Knowing which one to choose

Every cabling installation has a number of different requirements when it comes to chemical, abrasion and moisture resistance. When adding space limitations and temperature considerations into the equation, choosing the correct product can become difficult and confusing. Ultimately, ETS can provide a vast selection of Heat Shrink and Cold Shrink products to suit a wide variety of cable accessory requirements from low-voltage straight joints, all the way up to 72kV distribution line terminations.

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How the issue of galvanic corrosion affects installation of stainless steel trefoil cleats onto galvanised steel support structures in various environments.

The term galvanic corrosion refers to corrosion induced when there is electrical contact between two dissimilar metals in the presence of an electrolyte, i.e. water or corrosive vapour. The severity of the corrosion is determined by whether the metal is deemed cathodic, e.g. 316 stainless steel in its passive state, or anodic, e.g. zinc (the predominant metal of galvanised coatings).

In the majority of cable cleat installations, galvanic corrosion is not experienced due to the lack of an electrolyte in the atmosphere. Stainless steel has an inherent chrome oxide film layer which protects it from the environment, in what is deemed an “active” state, this layer can however be eroded in the presence of halogen salts in the form of fluorine, chlorine, bromine, iodine or astatine, many of which can be found in contaminated water or gas vapour. As the majority of ETS stainless steel cable cleats are installed within dry industrial or commercial environments, without the presence of any electrolyte and remaining in their “active” state, galvanic corrosion does not occur between the cleat and the surrounding galvanised steel support structure.

Cause and effect of galvanic corrosion

Galvanic corrosion is an issue which must be addressed in areas contaminated with high levels of halogen salts, namely exposed environments close to the sea or areas prone to contaminated rainfall, e.g. major conurbations and oil or gas fuelled power stations etc. In such areas the integrity of the stainless steel product is attacked by these halogen salts, breaking down the protective chrome oxide film, making the material deemed to be “passive” in its characteristics. Over a period of time and in the continual presence of an electrolyte, any zinc coated (galvanised) structure is adversely affected, dissolving the zinc and corroding faster than it would if not in contact with the passivated stainless steel, which conversely corrodes slower! In real terms, this means that the galvanised coated steel-work would corrode due to the loss of its zinc coating, although the stainless steel cleat suffers no adverse effects.

Avoid galvanic corrosion with a 91-ST washer

To overcome the issue of galvanic corrosion in such areas, we recommend the use of the 91-ST cleat separation washer. This provides an insulation layer between the dissimilar metals, increasing the distance between each metal and removing the electrical and physical contact points critical to the development of corrosion.

The importance to this process of time and “wetness” (as well as the chemical characteristics of the “wetness”) should be stressed. There is no definite period of time which can be mentioned as there are so many variables to the process, consideration should be paid to the projected life-span of the installation and the potential corrosiveness of the environment. In general terms, we would advise the use of the cleat separation washer for all external installations.

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