INDUSTRIAL BOILER & MECHANICAL
Used Boiler Inventory

Common Boiler Problems, Part 1: Low Water Conditions

 

Even though the use steam boilers have been used in industries since the mid 1800’s, we continue to encounter common problems with their operation. Some of the most common problems include:


  • Low water conditions
  • Improper blowdown techniques
  • Poor water treatment
  • Improper warm-up
  • Interlock testing
  • Training
  • Preventive maintenance
  • Proper documentation
  • Grandfathering old equipment
  • Human factor

Low Water Conditions

The potential for severe or even catastrophic damage to a boiler as a result of low water conditions is easy to imagine considering that furnace temperatures exceed 1,800 oF., yet the strength of steel drops sharply at temperatures above 800 oF. The only thing that allows a boiler to withstand these furnace temperatures is the presence of water in or around (depending on whether the boiler is a fire tube or a water tube design) the pressure parts at all times that a fire is present. Low water conditions will literally melt the steel pressure parts.

Typical industrial boilers are “natural circulation” boilers and do not utilize pumps to circulate water through the pressure vessel. These units rely on the differential density between hot and cold water to provide the circulation. As the water removes heat from the pressure parts, the water temperature increases and it rises to the steam chamber. Eventually, sufficient heat is transferred and steam is generated. Colder feedwater replaces the water that rises, which causes the natural circulation.

Due to the critical need for water, modern boilers are equipped with automatic low water trip switches. Some older boilers may not have these relatively inexpensive devices. If you boiler(s) do not have low-water trips, run, don’t walk to the phone and initiate their installation. You have an accident and expensive repairs waiting to happen. The needed repairs can range from, re-tubing to total destruction of the unit, if it is overheated. In the event of low water, the low water trips will trip the burner (or fuel flow for solid fuel boilers) and shut down the forced draft fan. This shuts down the heat input. A LOW-WATER CUTOFF IS A MAINTENANCE MUST!!!

The trips should be installed at a water level that will prevent damage. Low-water trips are generally installed approximately 6” lower than normal operating level. The control of the boiler water level is tricky and even the best tuned control systems cannot always prevent a low-water condition The “water level “ in a pressure vessel is actually a fairly unstable compressible mixture of water and steam bubbles that will shrink and swell with pressure changes and will actually shrink momentarily when more “cold” feedwater is added.

Some common causes of low-water conditions include:


  • Feedwater pump failure
  • Control valve failure
  • Loss of water to the deaerator or make-up water system
  • Drum level controller failure
  • Drum level controller inadvertently left in the ”manual” position
  • Loss of plant air pressure to control the valve actuator
  • Safety valve lifting
  • Large, sudden change in steam load

Unfortunately, an alarming number of boilers equipped with low-water trips are destroyed each year. Common reasons include:

  • Disabled trip circuits (A typical scenario involves disabling the trips to eliminate nuisance trips due to improperly tuned controls, etc. This involves a “band-aid” to cover the real problem and should never be allowed.)
  • Inoperative trip switches

Water conditions should be monitored closely, and addressed through proper routine maintenance to ensure operational efficiency and equipment safety. If you believe you are experiencing some of the challenges identified above, have a qualified boiler service company perform a system assessment to repair or replace equipment as required.


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(855) 753-BOILER

Industrial Boiler & Mechanical

3325 North Hawthorne Street

Chattanooga, TN 37406

 

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