Duck or Rabbit, Insulant or Bracket?

I’m sure most of us have seen the left-hand picture before. Do you see a duck or a rabbit? Apparently, what we see doesn’t just change from person to person - it also changes depending on our current circumstances. Looking forward to Easter? You’ll probably see a rabbit. Raining outside? Nice weather for ducks of course! Perhaps the only correct answer is a duck-rabbit!

How about the picture on the right? Do you see an insulation system or a bracketry system? The answer is again most likely affected by our circumstances. To the Thermal Insulation Specialist, load bearing insulation is a continuation of the insulation system and both thermal performance and compatibility with the insulation system is key. To the pipefitter the load bearing insulation is part of the pipe support system and load bearing performance is key. The insulated pipe support insert is of course both – a “duck-rabbit” of sorts – and it must fulfil its function as both an insulant and a load bearing support.

The problem is that insulated pipe support inserts are often only specified or installed with one viewpoint in mind. A focus on thermal performance alone does not guarantee that the insulated pipe support insert is fit for purpose at the specified loading requirements. A focus on load bearing performance alone does not allow for effective mitigation of energy losses.

This is an important consideration for the building services industry. The increased focus on minimising heat losses (particularly on heat network projects) means that insulated pipe support inserts are now specified as standard on heating and hot water services, as well as below ambient services. Anyone still applying brackets direct to pipe on these services really should become better acquainted with BS 5970:2012 and CP1 Code of Practice for Heat Networks.

At the same time, we also need to acknowledge that a misapplication of an insulation product beyond its load bearing capabilities is also an issue – one which could lead to failures and increased inspection and maintenance costs. Arguably the biggest issue here is in the misapplication of standard insulation materials to do a load bearing job – it is still far too common to see cut lengths of low-density pipe section inserted under brackets as a cheap - and wholly unsuitable - alternative to a load bearing insulated pipe support insert.

However, there is also a case that certain insulated pipe support inserts may be unsuitable for large pipe applications. For example, the pipework in large plant rooms could be crowded with valves and other pipework equipment – how do you prove that the insulated pipe support insert is suitable for application unless you calculate for the specific loading requirements of the pipework system?

Thankfully BESA Good Practice Guide TR70 has some useful guidance in this respect:

“For large diameter pipework, typically 200mm and above, specific loading calculations should be sought from the pipe support manufacturer. Where calculations are unavailable, alternative supports such as wood or silicate blocks may be acceptable. It should be noted that wood and silicate blocks have a lower thermal performance.”

Wood blocks highlight the whole “duck-rabbit” scenario perfectly. The thermal performance of wood is not in the same ballpark when compared to the insulated pipe support inserts marketed by thermal insulation product manufacturers. However, the load bearing potential could of course be advantageous. Depending on your circumstances you may have a very different view on this.

Perhaps the question should be “what should be done if wood blocks are required for the application”? First of all, wood blocks should be clearly tested for reaction to fire, thermal performance, water absorption/vapour barrier quality and load bearing performance.

Secondly, mitigating measures should be considered when wood blocks have been specified for application. BS 5970:2012 states the following:

“Incidental heat losses not directly related to those through the insulating material should be taken into account. NOTE: Such incidental losses include losses by conduction through the suspension or supporting system and losses from uninsulated areas, e.g. valve or damper control spindles and operating gear. These losses can add approximately 20% to the theoretical heat loss from the insulated system.”

We can therefore see how using wood blocks in place of low conductivity insulated pipe support inserts could push up the theoretical heat losses from the insulated system. We should therefore consider mitigating measures such as increasing the thickness of both the wood block and the specified thermal insulation system to compensate for the system energy losses.

It is of course important that all insulated pipe support inserts be tested to the same criteria. It makes sense that all products are tested for reaction to fire, thermal performance, water absorption/vapour barrier quality and load bearing performance. This may require a separate standard to ensure buy-in from all manufacturers.

Finally, the role of the Thermal Insulation specialist should not be underestimated. Early engagement is vital and both pipefitter and thermal insulation specialist should be appointed at early stages to ensure that the installation is planned according to the specification. This is a natural junction between trades and those appointing specialist contractors need to be able to see the rabbit and the duck.

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The earliest known version of the Rabbit-Duck is an unattributed drawing from the 23 October 1892 issue of a German humour magazine. After being used by psychologist Joseph Jastrow, the image was made famous by Ludwig Wittgenstein who included it in his Philosophical Investigations as a means of describing two different ways of seeing: "seeing that" versus "seeing as".