The Impact of Insulation on Electric Heat Trace Design & Operation
It was freezing, even for Midwestern standards. That morning I received a call from a plant manager at a renewable diesel plant, about two hours from home. An excited plant manager announced that he had 5 tankers waiting to be loaded and another 5 on the way. He was not able to load out to the trucks because the biodiesel had setup from being too cold and was blocking flow. He had identified the pipe that was causing the problem, and he wanted to me to come out to help troubleshoot.
When I arrived, the operators were hooking up temporary steam lines to wrap the pipes and rewarm them. Eventually the product warmed up enough that they were able to restart the pumps and load out the trucks.
When we walked down the problem line the root cause was plain to see, we identified sections of pipe where insulation was either missing or completely frozen. In several areas, we could see the heat trace on the pipe. I later learned that during the summer, a contractor had replaced some piping in the pipe rack without reinstalling the insulation and jacketing. As fall turned to winter, rainfall and snow melt entered into the insulation system on the vertical piping sections and soaked a large portion of the fibrous insulation, causing it to become an ice block once it got cold enough.
In this event, the plant not only had to pay for truck drivers to sit for hours, but also overtime for all the additional operators called in last-minute.
Heat management system failure is an expensive, but often avoidable cost when insulated with the right material.
During my career in heat tracing, I helped my customers diagnose problems with their heating systems. The first signs of a failed system are often times when a line has lost flow, or a rupture occurs. After determining the electric heating system was functioning, my attention would turn to the insulation and jacketing system.
In order for an electric heat tracing system to function properly, the insulation performance must be matched to the process design needs, not only on day one, but for the life of the system. The output of the heating cable expressed in “watts per foot” is matched to the heat loss permitted through the insulation. If the insulation gets wet or damaged, the system will fall out of balance creating problems.
When designing a complete heat management system, it is important to consider the long-term performance of the insulation over-top of it.
Heat, water and mechanical damage – the three enemies of thermal insulation.
Wet or damaged insulation can cause costly failures to a process, resulting in frozen or plugged lines. These failures are not only costly to repair, but can also cause a loss of production and unplanned outages. In some cases, the failure of a heat tracing system can also create a health and safety risk if eye wash stations or active fire protection equipment freezes.
A common misconception is the jacketing or cladding over-top insulation will prevent water from entering the insulation system. In my experience:
- Operators walk and step on the piping to perform maintenance or access hard to reach areas, which causes damage to the system.
- Jacketing is removed but not reinstalled correctly.
- The process of thermal cycling can cause expansion and contraction of the insulation and jacketing.
When this happens, penetrations in the jacketing can cause water to flow in and come into contact with the insulation material. Traditional water absorbent insulation will hold moisture next to the pipe, resulting in an imbalance between the heat available from the tracing system vs. the increased heat loss through the wet insulation.
Even as little as 3% moisture uptake will result in a 3-4X loss of energy. This imbalance will cause the system to fail. Water soaked insulation will result in a greater heat loss and the potential for the piping to freeze or plug if no flow occurs. If wet insulation persists it can also increase the risk of corrosion under insulation.
Pyrogel® is engineered to resist the typical enemies of mechanical insulation; heat, water, and mechanical damage.
Another important consideration when selecting insulation for a heat tracing project is the thickness. A well-insulated system may reduce the number of circuits required for a project. A heat tracing system with less circuits can decrease power distribution costs. This will result not only in a lower total installed cost, but also a reduction in operating cost.
Solving insulation’s toughest challenges
Almost two decades ago Aspen Aerogels set out to re-imagine thermal insulation, the result of that effort became known as Pyrogel, uniquely designed to maintain performance even when the jacketing system has failed. Pyrogel’s multilayer system allows for staggered circumferential and longitudinal joints that make it near impossible for water to penetrate. Unlike traditional insulation, Pyrogel can resiliently resist water or snow ingress, keeping the asset dry and helping the heat trace system to operate as designed.
Pyrogel’s ultra-thin profile, up to 50% thinner than traditional insulation also helps to resolve clearance issues, a common problem that can limit the thermal resistance that can be applied over a heat trace system.
Finally, in the event of a heat tracing cable failing or is damaged, the insulation will have to be removed for that repair or inspection. Pyrogel is a flexible aerogel blanket designed to be removable and reused. At one of our customers in the Midwest, Pyrogel has been removed, stored and then re-applied for three separate maintenance events.
Looking back on my time supporting electric heat trace, it still amazes me how many issues were caused by wet or degraded insulation, those issues were costly to my customers. Now at Aspen Aerogels, I feel that we have the tools to help heat trace perform as intended. If you recognize some of the issues described above, feel free to get in touch with me or a colleague, we will be delighted to assist.