A firetube boiler is a boiler where hot flue gas passes through the tubes set within the water vessel. The burner fires through the blast tube, generating heat throughout the firetubes. The generated heat flows through the tubes and heats the surrounding water by way of convection. Like with any heating equipment, there are potential dangers if the boiler is not consistently maintained. A water leak from a firetube boiler can be hazardous, which is why it is essential to take precautionary measures to limit the damage or even prevent the boiler water leak from happening. To maximize the life of your boiler, preventative maintenance should be conducted throughout the year, including periodic inspections per the Department of Buildings, repairs, and replacing parts when necessary.
What Causes a Firetube Boiler Water Leak?
Understanding the common causes of a boiler water leak and the locations on the unit they occur is crucial to prevent a leak before they transpire. In firetube boilers, leaks often materialize on the tubes, tube sheet, shells, and gaskets. However small it may be, a boiler water leak is often the first sign of upcoming issues in the boiler and, if left unaddressed, will lead to even more costly repairs and boiler downtime. Let’s look at some of the most common causes of leaks in firetube boilers:
- Fresh Water: The water in a firetube boiler is one of the most important components in a boiler system. Boiler feedwater is drawn from steam condensate, hydronic return water, and freshwater. Freshwater will add to more mud sediment accumulating on the bottom of the boiler if the unit is not drained and flushed periodically and properly treated. It is also important to monitor the amount of water used in your boiler to detect any inconsistencies. Installing a water meter is a great way to monitor the amount of freshwater added to the boiler. Boiler water readings should be observed and recorded weekly. A significant increase in between readings is a major indication that there is a water leak somewhere in the heating system. Higher readings often indicate excessive water loss, which should be reported, investigated and corrected to prevent pre-mature boiler tube failures and deterioration of the boiler steel.
- Water Chemistry: The water chemistry in a boiler plays a significant factor in optimizing efficiency. When freshwater is added to the system, it must undergo chemical treatment to limit corrosion. Boiler water must be properly treated to establish balanced water chemistry for operation, and untreated water should never be used. The treated water protects against corrosion and the build-up of mud and solids. If the water chemistry is incorrect, such as too much or too few chemicals, there will be adverse effects. A common chemical used is sodium nitrate with a copper and iron inhibitor. Although chemical treatment does not entirely prevent corrosion, it will drastically slow down the process and extend the life of your boiler. When performing a chemical treatment, the balance of chemicals must be satisfactory to achieve the best results. Adding too much chemical will cause the boiler to surge and leak while adding too little will not effectively prevent bacteria and corrosion. The boiler water is tested for PH, conductivity, chloride, and nitrate with meters and reagents; each condition tested has its parameters that they must stay in for optimal balance. Chemical treatment will help maximize the efficiency of the unit and reduce energy costs.
- Scale/Corrosion: Scale accumulating on the mud leg and corrosion on the tubes are common problems that will cause issues with your boiler as the scale and corrosion worsen. When the boiler is not periodically drained and flushed, mud settles on the bottom of the mud leg and prevents the steel from cooling. The built-up mud will debilitate the heat transfer process in the tubes, forcing a more considerable amount of fuel to be used to continue the operation. Even a thin layer of scale will affect the heat transfer because it serves as an insulator. The firetubes are the thinnest part of the unit, making them susceptible to cracks and leaks. We recommend consistent maintenance such as boil outs, fireside, and waterside boiler cleanings. The firetubes are also subject to oxygen pitting due to excessive make up water and if the temperature conditions of the water inside the boiler are not stable. Oxygen pitting occurs when excess oxygen is in the boiler water due to feedwater temperatures dropping below standard operating conditions.
- Thermal Shock: Thermal shock is a less common problem that affects the tubes but can still cause a leak or burst. Thermal shock occurs when there is an extreme difference in the feedwater temperature as it enters the boiler. Thermal shock is different from oxygen pitting in that it causes damages immediately. The internal components of the boiler where the tubes reside are extremely hot. Therefore, when cold water enters the boiler, the result can be critical damages to the tubes and other parts, such as the feedwater connection. Properly piping the feed water to the boiler or feed water tank will minimize the potential problems.
How Does a Tube Leak Affect the Boiler?
Firetube boilers encompass many advantages; they are high-efficiency machines that are typically cost-effective in maintenance and do not require the use of only pure water to operate. However, a water leak will prevent the boiler from operating at peak efficiency. The effects of a boiler leaking water expand beyond just tube repairs, and the causes discussed in this article are only some of the issues that can arise in a poorly maintained boiler. Leaks can cause secondary damage to other parts of the boiler and even damage the entire unit, especially if not treated right away. Identifying a boiler water leak when it first occurs is essential to avoid costly repairs, maintenance, and even potentially extreme accidents in a boiler room.