Air Venting and Pipe Insulation in Steam Distribution

Air Venting:

A pipe is filled with air when steam is initially introduced into it after a period of inactivity. Along with the steam, large amounts of air and other non-condensable gases will enter. These gases will build up in the pipes and heat exchangers when the steam condenses. Therefore these gases should be discharged while taking the precautions so that the consequences are not faced. Non compliance of Air venting procedure will result in prolonged warming-up period and decreased plant and process performance. It will also impact the temperature and Pressure of the System. Within the system, air will create its own pressure, which will be added to the steam pressure to create a total pressure. As a result, the steam/air mixture’s real steam pressure and temperature will be lower than what a pressure gauge would indicate.

Automatic air vents for steam systems should be installed above the condensate level so that only air or steam/air mixtures may enter them. These vents work on the same principles as thermostatic steam traps. The figure shows the appropriate location of the Air vents which is at the position where the Steam Mains Terminate.

Air Venting

Fig 1. A typical example of Air venting

An air vent’s discharge needs to be routed to a secure location. In real life, an air vent discharge can be absorbed by a condensate line that is falling towards a vented receiver.

For better efficiency of the system, Air vents can also be fitted at the below places:-

1.  Along to a thermodynamic trap or, in certain cases, an inverted bucket trap. On start-up, these traps might occasionally be sluggish to release air.

2.  At the large steam spaces, where the air jacket is already present.

Pipe Insulation:

To slow the heat transfer from the system to the environment, insulation of steam conveying pipes and steam-consuming equipment is crucial. The steam pipe insulation will serve the following purpose:-

     1.    Reduce heat loss to save energy.

     2.   Better control of Temperature in a process.

     3.   Avert steam condensation.

     4.   Prevent or minimize pipe damage from contact with flames or corrosive environments.

     5.   Regulate surface temperature for comfort and personal safety.

Effect of Insulation

Table 1. Effect of Insulation on Steam Pipes

The thickness of insulation that is most cost-effective will depend on a number of variables:-

1. Cost of Installation

2. Size of the pipe network

3. Temperature of the steam

4. Heat carried by steam

5. Damping

6. Wind speed (if piping is external)

With the exception of safety valves, it is crucial to insulate all hot components of the system. This pertains to all mains’ flanged couplings, as well as the valves and other fittings. In the past, it was normal practise to trim back the insulation on either side of a flanged junction so that the bolts could be accessed for maintenance.

Calcium silicate, mineral wool with an aluminum coating, and fiberglass are frequently used in installations. Insulating material must not be damaged or allowed to clog with water. Particularly in outdoor situations, adequate mechanical protection and waterproofing are necessary.