Mechanical Integrity Includes 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 -50oF (-28 to -45oC) 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.
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.
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.”