They say that April showers bring May flowers, but this is not the case in the Seattle area where I live. April showers bring May, June and July showers and occasional sun breaks three days in August. However, my role in our company involves traveling all over the Western U.S. and Canada, which allows me to experience the light and warmth provided by that unfamiliar, bright orange ball in the sky…
Summertime can create specific challenges for your insulated piping system. In many parts of world, extreme temperature swings during the summer can have a significant impact on the expected surface temperatures of hot piping systems, which can increase the potential for skin-contact injuries. How does this happen?
There are many conditions that influence the performance of an insulated pipe or vessel and make it potentially unsafe for personnel during the hottest months of the year. The following are the most commonly used design considerations when calculating the thermal performance of insulation for above-ambient to high-temperature range:
- Base metal type
- Pipe or vessel diameter
- Orientation (horizontal or vertical)
- Process temperature
- Ambient air temperature
- Wind speed
- Insulation type
- Jacketing material (emissivity)
During the summer, the two variables that heavily influence system performance are higher ambient air temperatures and changes in wind speed. In many areas of the world, including the U.S. Gulf Coast, temperature swings can reach extremes from winter to summer. For instance in Houston, TX, the lowest temperature ever recorded was 9°F (January 1989) and the highest was 106°F (August 1962)[i]. Plant managers have to take these potential extremes into consideration as they look at what insulations will best meet their requirements.
For an easy example of how external temperatures affect thermal performance, take a look at a 12” stainless steel pipe, operating at 600°F, with 3” thick expanded perlite insulation.
At 50°F ambient / 5 mph wind speed: Surface Temp = 131.5°F (safe to touch per ASTM C1055) At 95°F ambient / 0 mph wind speed: Surface temp = 177.3°F That’s almost 46 degrees hotter, meaning the same pipe will cause contact burn injury on bare skin just by a simple change in the weather. Looking at the numbers, it’s easy to see how a given insulation system can be affected by the higher ambient air temperatures and the still summer air during the “dog days of summer”.
Keeping this in mind, it’s clear that designing insulation systems to average annual temperatures and average wind speeds will create conditions that are not safe-to-touch during temperature extremes. It is a much better practice to design conservatively and use the highest expected summer temperature, zero mph wind speed and the emissivity of new metal jacketing. The risks from higher seasonal surface temperatures and potential burn injuries to workers outweigh any extra cost of using the correct thickness of insulation that will keep your system safe to touch all year long.