Avoiding Corrosion Under Insulation

14 September 2020

Technical Thursday: Avoiding Corrosion Under Insulation

Here at Belgrade, we pride ourselves on our ability to stock and supply the materials our customers need, when they need it. As a trusted distributor for many of the construction industry’s key manufacturing brands, we’re also able to tap into a network of technical experts to extend our service offering for the benefit of our customers.

In the first of our Technical Thursday blogs, we’re partnering with Armacell to look at how insulating pipework and support brackets with the same material can ultimately improve energy efficiency and protect against corrosion under insulation (CUI).

What is CUI?

CUI can be a major issue in the HVAC and process sector, and severe cases can often put systems, and reputation, at risk. Representing all types of corrosion that can occur on the pipework surface beneath an insulation system, CUI can be triggered by multiple factors or conditions.

The biggest pain point? CUI occurs hidden beneath the insulation, and often is discovered later when the damage is done.

CUI occurs due to the moisture build-up on the external surface of insulated equipment, and one of the most common types of CUI is bi-metallic, or galvanic corrosion. This type of corrosion is the result of very small electric currents in the presence of moisture and oxygen between two different metals. The more anodic metal of the two will corrode when this happens. For example, copper pipework with steel fittings and hanger brackets will result in the steel undergoing accelerated corrosion.

However, just because two metals are used on a system it doesn’t mean accelerated corrosion will definitely occur – it’s just a case of following a few basic rules to mitigate the risk.

How can we mitigate CUI occurring?

In most cases insulating the pipe, fittings and hangers with an appropriate material will separate the two metals, eliminate condensation and help to mitigate the risk of any galvanic corrosion. Considering how different metals react will help when choosing the most suitable insulation material.

Stainless steel pipework is susceptible to stress corrosion cracking simply by the presence of chloride particles against the pipe surface particularly when combined with moisture and operating temperatures above 35°C. To mitigate the risk of corrosion on steel pipework, it is recommended to use a material that therefore doesn’t contain halogens.

It’s also worth understanding that copper pipework can fall victim to crystalline stress corrosion cracking, which is the result of ammonia or nitrides combined with moisture. Again, choose an insulation material that doesn’t have a large mass share of ammonia in the material makeup.

Don’t forget the pipe support brackets

Whilst we consider the behaviour of different metals on the pipe work itself, it’s crucial to consider how pipe support brackets can be a potential trouble spot when it comes to CUI too.

It’s important to choose a pipe support hangar bracket that doesn’t compress the insulation, and maintains the same thickness along the length of the pipe. This is because an all too common problem with pipe support brackets is that they can place the copper and steel in closer contact through compression, which causes galvanic corrosion.

For chilled applications, pipes should be isolated from their mounting element with an adequate insulation thickness taking into account the pipe size, line temperature, relative humidity and of course the chloride content of the material.

To achieve a reliable connection between the clamps and the insulation, it’s key to source a compatible pipe support from the same insulation manufacturer as this will ensure you’re matching nominal wall thickness and system performance.

That’s why insulating both pipework and pipe support brackets plays an important role in maintaining system efficiency and integrity. An integrated approach, where the insulation materials are from a single source offers greater compatibility in terms of condensation control, fire behaviour, energy saving and ease of installation.

If you would like more advice on technical insulation, Belgrade is here to help. Our team work closely with manufacturers to provide technical advice and support when required, so get in touch today and we’ll be happy to help.

Belgrade offers a range of technical insulation solutions and accessories, including AF/ArmaFlex Class O and Armafix supports, across all our branches. Take a look at our brand new Technical Insulation Price Guide and get in touch with your local branch to place your order.