Poor Installation Practices Affect Performance

Since it was founded more than 30 years ago, IIAR has stressed safety in the design and operation of ammonia refrigeration systems. A significant amount of the focus has been on the mechanical integrity of the piping, valves and components. However, IIAR may not stress the role of insulation enough. Refrigeration system owners and operators should be aware of the potential safety problem with faulty insulation.

Over the years, I have observed insulation on piping and vessels in all types of industrial refrigeration systems. Often, the insulation is doing the job it is intended to do, and doing it well. But, I’ve also seen various types of insulation such as extruded polystyrene, urethane, cellular glass and elastomeric -- particularly in the low temperature -20 to -50^oF (-28 to -45^oC) areas -- that were not installed properly from the beginning. The pipes and vessels were not sandblasted and cleaned of rust; they were not painted; some had little or no vapor barrier installed and some had no jacketing installed. I’ve seen ice formations on pipes that seemed heavy enough to cause the piping system to fall to the floor. This ice added excessive loads to the hangers and roof structure. And, I’ve seen liquid recirculators that had so much ice on them, they were difficult to recognize even though they were operating.

Poor insulation installation practice can create a safety hazard. It really doesn’t matter what type of insulation is employed. Granted, flexible elastomeric and fiberglass insulation does not perform as well at low temperatures as many other types of insulation do and normally are not recommended for such installations. Still, I’ve seen several systems with this type of insulation and, needless to say, few -- if any of them -- have lasted more than five years.

When insulation vapor seals are faulty because there are breaks and holes in the seals, moisture can accumulate under the insulation. This moisture causes the pipe to corrode until the pressure in the refrigeration system exceeds the bursting pressure of the damaged pipe, and then you have ammonia (NH3) or R22 on the loose. Neither of these refrigerants is fun to be around under these circumstances.

I recently surveyed a fairly large refrigeration plant that I previously surveyed back in the mid-90s. My initial recommendation was to replace the insulation on all of the cold piping and recirculators. Well, the company had some hard times, and none of my recommendations to correct the insulation problems were followed. The new recommendations were the same as the older ones. The insulation was even more damaged. In some cases, it was beyond repair. It really needed to be replaced along with all of the insulated piping, which was extremely rusty. I suggested to the plant owner that the piping could fail at anytime. Well, about a week after the report, a pipe started to leak. Fortunately, the leak was stopped without any problems.

Unfortunately, this is not an isolated case. We have learned a lot in the past 20 to 30 years about installing insulation, and in most cases, it is installed properly. But, there are many ammonia refrigeration plants out there, built in the 1950s, 1960s and 1970s, that probably do not have viable insulation systems. If their maintenance personnel was not on top of every break in the insulation jacket or the vapor seal, repairing it promptly, there is reason to suspect that moisture has penetrated the insulation and is now attacking the pipe. The rusting is hastened by the presence of nitrates and sulfates -- components of most types of insulation. Such systems should be investigated thoroughly during a mechanical integrity inspection.

Equally unfortunate is the fact that in many cases, it is next to impossible to replace insulation in a food plant that is operating many hours and most every day except Sunday. Most processing plants are not going to shut down for several weeks to have insulation replaced. Here we have assumed that the piping is inside the building as most piping was during the early years. One approach to this problem is to install new piping on the roof; then, the only in-plant work would be disconnecting the air-handling unit (AHU) from the existing piping and reconnecting it to the new piping. This can be done on weekends. Where plants can shut down for a reasonable time, even if the pipe needs replacing, re-insulating is simple. If the plant is 25 to 30 years (or more) old, I also recommend that the stop and control valves be replaced on all AHUs, as chances are the old valves do not work properly.

Good insulation practices include having well-trained installers. To install the insulation, you should:

• Sandblast the pipe or vessel.

• Apply a good epoxy primer for rust prevention.

• Install two or three layers of good insulation in accordance with the manufacturer’s recommendations, including a vapor seal mastic at all seams and over the insulation.

• Apply a good jacket with CPFC indoors and metal outdoors.

Some insulators have used fiberglass fabric and mastic on fittings; however, that is not adequate. In these installations, hail can damage the insulation if it is on the roof. Another reason this installation practice is inadequate is that birds like insulation -- I’ve seen seagulls get extremely high on urethane. All fittings should have jackets similar to the straight runs. Stainless steel and white painted aluminum are excellent for jackets.

For a thorough description of the proper way to install insulation for industrial refrigeration systems, see Chapter 7 of the “IIAR Ammonia Refrigeration Piping Handbook.”

Links

• International Institute of Ammonia Refrigeration (IIAR)
• Chill Factor: Complete Column Archives