Drainholes or Drainplugs

A statement that is often copied within the insulation industry originates from a NACE/AMPP “standard” SP0198. And it simply states that:

“…the insulation system that holds the least amount of water and dries most quickly should result in the least amount of corrosion (CUI) damage to equipment”.

A simple and effective description.

By the way, my below stated plea is not just about CUI but about moisture. Although moisture can be a? cause of CUI, it also deteriorates the thermal properties of insulation materials. A fact every expert in the insulation world knows, but how we get rid of moisture is often less known.

In temperature range where CUI most commonly is detected, mineral wool is often used. Due to its inherent vapour-permeable structure, this material can absorb moisture more easily than a closed cell material. Although absorbed moisture doesn’t necessarily cause CUI, it always decreases insulation thermal conductivity. And for that reason alone it’s paramount that moisture which has penetrated the insulation system can evaporate or drain from a vapour-open insulation.

A proven system predominantly seen in Germany which is based on allowing moisture to evaporate is called "hinterlufted" insulation. Creating an air cavity between the insulation and the metal jacketing by using studded foil, moisture can condensate against the colder jacketing and as condense droplets easily escape through a drain hole at the bottom.

Since I already started with a standard, let's stick to a few others like below AGI-Q152 and DIN 4140.?

So far in line with the thinking from SP0198.

But the above described moisture is usually moisture from the environment which due to a shift in the dew point condensates within mineral wool in the outer region of the insulation system.

However, moisture or (rain)water that enters the insulation-system through other ways, will have to be dealt with in a different manner. Water ingress not only because of damaged jacketing, often due to foot-traffic. But also water ingress along flashed protrusions where sealants/caulking have failed over time. Most insulation materials have a approx. 20 year lifespan. But I don’t know of any sealant under normal operating conditions that lasts that long. Which inevitably means sealant/caulking’s need regular inspection and/or maintenance.

The use of sealant/caulking is for a long time and widely discussed. In some cases for reasons related to application, e.g. not between but on top of jacketing overlaps. But for a big part, as said before, no sealants have a life-span near to insulation materials. In other words, if sealant are installed in critical places where a failure of sealants leads to water ingress, these places should be regularly inspected. Which in my experience seldom happens.

To refer to another standard. CINI manual doesn’t describe the use of sealants at all. For reasons that according their opinion it’s always possible to install jacketing in a watershed fashion. To me this is highly theoretical and for an ideal world. In my experience a see a lot of situations, existing as well as new build situations which require the use of sealants/caulking. ?And besides this, a lot of other standard describe sealants. Besides previous mentioned also BS-5970, PIP-INEG-1000 and API-RP-583 refer to the use of sealants/caulking’s. Based on all of these standards I humbly conclude that sealant/caulking’s are still necessary.

But back to where I started: the drain-hole.

Within this air-cavity as described in AGI-Q-152 and DIN 41404 moisture which has condensed to droplets on the inside of jacketing will have no resistance and freely find its way to the lowest point via a drain-hole into the ambient surroundings. But the CINI manual describes drain-holes in jacketing that is fitted tightly over the insulation, so without an air cavity. As far as I know, the effectiveness of this has never been demonstrated and it seems to me that it has little added value.

The NORSOK R-004, on the other hand, specifies that drain holes must penetrate the entire insulation, which to me seems logical. How else can moisture/water which has found its way to the pipe can have an unhindered path to the ambient surrounding’s. Mineral wool may have a vapour-permeable structure it still provides a barrier to water. So, if this water can’t freely escape through a drain-hole it most likely eventually will be socked up.

With that NORSOK standard in mind, a plastic drain-plug called the PMU was developed in Norway (partly by Statoil) more than 20 years ago. Through our Norwegian trading partner, we as Temati included it in our product range and over time further developed it. In addition to the standard drainplug which is made of fire-retardant plastic, we also developed a type with 30 minutes of hydrocarbon fire.

Often I’m asked whether these drain-plugs work. And I have to admit that due to a lack of testing standards, I can merely refer to the basic laws of physics that many of us learned at school. Which is: Moisture moves to the environment where the vapor pressure and temperature are lowest. So condenses against cold jacketing. And condensed moisture and/or (rain)water responds to the laws of gravity, in other words it wants to go to the lowest point.

So until the time there is a generally accepted test, this is my explanation to the best of my knowledge.

But knowing that much in our industrial insulation world has evolved from “Trial & Error to Best Practice”. And even the above mentioned standards are originated along this principle.

To come to my conclusions. Starting with the statement from NACE/AMPP mentioning two things.

1. a systems that holds the least amount of water.

In my opinion should be translated into a system that is as water tight as possible. As per below excerpt from BS-5970:

• ensuring cladding overlaps on all circumferential and longitudinal seams are sufficient;
• positioning longitudinal cladding seams away from the prevailing weather and more than 90° from the vertical position;
• installing valves with the spindles placed horizontal or below;
• using a sealing compound to seal all protrusions through insulation and cladding;
• installing cladding overlaps to shed water (weatherwise – roof tile method);
• installing horizontal flat cladding with a fall or slope to shed water and avoid pooling;

2. a systems that dries most quickly.

In my opinion as system with either an air-cavity in combination with drain-holes or a system with drain-plugs.