Manhole Insulation

This article was written by Meghan Reilly of Thermaxx Jackets & John Barker of Midco Insulation

A few years back, a very good customer asked Thermaxx and our partners at MIDCO insulation to perform an insulation audit in multiple manholes on a line running through a busy urban area. The customer expressed some apprehension and frustration because previous attempts at insulating these lines were unsuccessful, as the insulation quickly degraded.

We agreed to help this customer address their heat-loss issues using a two staged approach:

  • Stage 1 – Review mechanical drawings, steam pressure and photos of existing system.
  • Stage 2 – Thermaxx & MIDCO field technicians made a site visit to evaluate the system in place, take measurements and temperature readings for savings analysis and material orders.

Field technicians that visited the site were all OSHA & confined space trained. Personal protection is at a premium in steam vaults due to the lack of adequate space, elevated temperatures of the piping systems, and sometimes limited airflow.

Insulators were faced with unique challenges when covering pipes and valves in steam distribution systems i.e. manholes, tunnels, vaults, and pits. Manhole insulation is the most complicated, because of the harsh environment. Providing proper insulation in steam vaults, both jackets and hard insulation, was essential due to the extreme design conditions created by the exposure to outdoor conditions.

Material specification is extremely important in order to prevent degradation over time. As mentioned previously, extended exposure to outside elements can cause flooding. The floods can contain sewer water, road salt, dirt and other corrosives. Because of this the insulation had to not only be thermally efficient but also weather-proof to maintain the integrity of the system.

Only closed cell insulation with a low moisture absorption rate should be used in manhole applications due to constant exposure to moisture. These manholes were originally insulated with fiberglass which is why they quickly broke down and had no thermal value. In addition to the closed cell insulation or foamglas, removable jackets should be installed on valves and expansion joints. It’s important that removable insulation is installed on the serviceable component so that the insulation is not ripped off during preventative maintenance. Thermaxx has designed a jacket specifically for manhole applications. The jacket is made of pure Teflon PTFE, pyrogel, a hydrophobic, high temperature insulation.

Pyrogel can also be used instead of, or in tandem with closed cell insulation. Pyrogel is recommended on systems with elevate temperatures and where space surrounding the piping is minimal. Pyrogel has a much greater resistance to heat loss per inch of thickness than most other insulation materials on the market. Pyrogel is also recommended on large diameter piping and vessels since it is a more flexible material which lends itself to custom dimensions. For this specific project, Thermaxx and MIDCO used a combination of Foamglas, Pyrogel and removable jackets.

Jacket Materials per Operating Temperature for Steam Pits and Vaults:

100-299°F

300-374°F

375-450°F

Jacket – Hot Side

Teflon

Teflon

Teflon

Thread

Kevlar Thread

Kevlar Thread

Kevlar Thread

Insulation Layer 1

10mm Pyrogel

15mm Pyrogel

20mm Pyrogel

Jacket – Cold Side

Teflon

Teflon

Teflon

Fasteners

Teflon Straps

Teflon Straps

Teflon Straps

Seal Flaps

Hybrid 7.0

Hybrid 7.0

Hybrid 7.0

The last piece of the puzzle is possibly the most important when it comes to preventing degradation of an insulation system in a manhole is protective jacketing. Insulation for these distribution systems were designed with a protective jacketing i.e aluminum jacket, or self-adhering direct burial jacketing. This will protect the insulation from damage long after the install is complete.

Following our staged approach and adhering to the design specifications, made for accurate heat-loss analysis, a comprehensive scope of work, and a safe and successful install.

Contact Meghan Reilly and John Barker to discuss insulating your distribution system and to schedule a survey!

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