On hot lines, insulation is there to keep heat inside. On cold lines the direction reverses, and heat flows from the outside in. That single difference changes the whole design approach. In cold insulation, the main issue is not only limiting heat gain but preventing condensation from forming on the surface.
Why Condensation Forms?
Air always contains a certain amount of water vapour. When that air meets a cold surface and the temperature drops below the dew point, the vapour turns into liquid and droplets appear on the surface.
The sweating seen on a cold pipe is the result of this process. The dew point is not a fixed value; it changes with ambient temperature and relative humidity. In a humid environment the dew point rises and condensation begins more readily.
The Problems It Creates
Condensation is not merely a cosmetic issue. Water collecting on the surface can start corrosion on the metal over time. Moisture entering the insulation material raises its thermal conductivity, and insulation performance drops.
As performance falls, the surface becomes colder still, condensation increases and the process feeds itself. This is why moisture control matters as much as the thermal calculation in cold insulation. Water pooling on the floor also creates a slip hazard from a safety point of view.
What the Vapour Barrier Does?
The vapour barrier used in cold insulation is the layer that stops humid air from moving into the insulation. Unlike hot applications, this layer sits on the outer face of the insulation, because moisture travels from the outside inwards.
The integrity of the barrier determines its performance directly. A small opening left in the layer can weaken the entire system. Lapped joints, complete taping and avoiding penetrating fasteners are therefore the basic rules of the application.
Material Selection
Closed cell materials are preferred on cold lines, since this structure limits how much water vapour the material can absorb. Closed cell elastomeric rubber is the most widely used material in this group.
At lower temperatures and in cryogenic applications, foam glass and polyurethane based materials come into consideration. The choice depends on operating temperature, pipe diameter and ambient conditions. You can review the scope of our work on our insulation page.
Thickness Calculation
In cold insulation, thickness is calculated not only against energy loss but to prevent condensation. The calculation uses line temperature, ambient temperature, relative humidity and the thermal conductivity of the material together.
The aim is to keep the outer surface temperature above the dew point. Where humidity is high, the same line requires a thicker application. Two similar lines, one indoors and one outdoors, may therefore be insulated to different thicknesses.
It is important that the calculation reflects actual site conditions. Mod Endüstriyel Servisler carries out this assessment using the plant's own operating data.
Critical Points in Application
On straight pipe sections the work is relatively straightforward. The real difficulty lies in the details. Valves, flanges, elbows and support shoes are where continuity of the vapour barrier is most often broken.
At support points, insulated load bearing supports are used to avoid a thermal bridge. Where a metal support touches the pipe directly, condensation at that point becomes almost unavoidable.
At valves and flanges, which require frequent access, removable solutions are preferred. Insulation jacket applications provide both maintenance access and continuity at these points.
Multi Layer Application
At low temperatures, a multi layer application is preferred over a single layer. The joints of each layer are staggered so that they do not align, which reduces thermal bridging.
The expansion allowance between layers is also part of the design. Materials change dimension as temperatures shift during start up, and without that allowance the joints can open.
Integrity Lost During Maintenance
One of the most common problems on cold lines is an incomplete vapour barrier after maintenance. If the reopened section is not lapped and taped with the same care as the original work, that point gradually becomes an entry route for moisture.
Recording the areas where work has been carried out, and reviewing them first at the next inspection, is therefore worthwhile.
Checks After Commissioning
Once the system is running, the first check is simply to look for sweating on the surface. Localised sweating at particular points indicates either damage to the barrier or a thermal bridge at that location.
Repeating these checks as the seasons change is sensible. A line that caused no trouble in winter may begin to sweat once humidity rises.
Frequently Asked Questions
Why is the vapour barrier placed on the outside of the insulation?
On cold lines, moisture travels from the outside inwards, so the barrier meets that movement on the outer face. In hot applications the situation works the other way round.
How is thickness determined in cold insulation?
Line temperature, ambient temperature, relative humidity and the thermal conductivity of the material are calculated together. The aim is to keep the outer surface above the dew point.
What should be done if sweating appears on the surface?
Sweating can indicate damage to the barrier or a thermal bridge. A local inspection is needed to identify the cause.
Can the same thickness be used for the same line at every plant?
No. Because ambient humidity and temperature differ, the same line may require different thicknesses at different sites.