Cleaver-Brooks - Complete Boiler Room Solutions

Boiler Steam System Supply Basics

Tip Sheet: December 2015

Key Facts

  • A pound a water expands 1,600 times when it is converted to a pound of steam
  • Piping supports and expansion joints are necessary in a steam piping system
  • Steam traps not only trap steam, but they also remove condensate and air

The boiler is part of a cohesive system, just like the human body with the heart (boiler) pumping blood through a venous system consisting of arteries (steam supply) and veins (condensate return). The piping should be considered an extension of the boiler because if it ruptures, it’s an unfired pressure vessel, and bad things can happen, just like in a human arterial system.

Following are some major points to remember when considering a boiler steam supply system. 

It is important to know the correlation between steam volume and pressure. A pound of water occupies 0.017 cubic feet. Once it converts to a pound of steam at zero gauge pressure, it expands to 26.4 cubic feet, which represents an expansion of 1,600 times. Interestingly, as the operating pressure of the system increases, the pound of water converted to steam reduces in its volumetric size, and though the expansion is less when released to the atmosphere, the velocity of the accelerant is greatly magnified. 

When hot steam travels through a rigid piping system, piping supports and expansion joints need to be added to accommodate for the growth. One of the more popular methods is a piping loop arrangement that enables the piping system to expand and contract as the temperature in the piping rises and falls.  

Another technique is the sliding joint, often used because it takes up less space and is very effective; however, it must be rigidly anchored and guided in accordance with the manufacturer’s instructions. Expansion bellows is another option that does not require packing like the sliding joint.  

Insulating piping in a steam system is important to avoid significant heat loss. BTUs are lost due to the difference between the pipe temperature and the ambient temperature around it. As the pipe size increases and/or the temperature difference increases, the loss becomes greater. This not only constitutes a loss of energy, but can exacerbate water hammer too. 

It is important to follow the recommendations regarding velocity for both low- and high-pressure steam applications. Exceeding these recommendations can lead to serious problems, including high pressure drop, which impedes the steam from getting to the user in the quantities required. There is also the possibility of erosion caused by the velocity and abrasive characteristics of steam and some water droplets speeding across the inner walls of the pipe. It should be noted too, as steam travels through the pipe at speeds approaching or exceeding 100 mph in some cases, there is an increased chance of water hammer. The banging and shaking of steam pipes is an indicator of this dangerous condition, which needs to be fixed promptly.  

Addressing water hammer begins by properly capturing the condensate while it is forming. This means having properly sized drip pockets at the appropriate intervals (about every 150 to 300 feet) and before turns, low spots, end of the main and ahead of expansion joints, valves and regulators.  

Steam traps in a system are necessary as they trap steam as well as remove condensate and air. Though steam traps are not the total answer to removing air in a steam system (as air vents are still very necessary), they do assist in this essential removal. 

When selecting and sizing steam traps, remember the acronym LAMBS. 

  • Determine the Load or pounds of steam per hour. 
  • Consider the Application. Is it outside? In a dirty environment? Does the process require continuous draining? 
  • Is the application Modulating or constant?  
  • Could there be considerable Back pressure exerted on the trap, thereby reducing its differential? 
  • What is the Supply pressure? 

There are various types of steam traps available. The ones that are most commonly used can be divided into three distinct categories: thermodynamic, mechanical and thermostatic. Every trap has pros and cons and should be selected based on the application and conditions of the system.

To learn more about piping, including the types of steam traps available, watch the Boiler Steam System Supply Basics webinar.