Tube Inspection in FireTube and WaterTube Boilers

Boilers fall into four general distinct categories, low pressure stack (haystack) boilers and flued boilers are the first two, both of these are early designs not utilised much these days. The remaining two types are fire-tube boilers and water tube boilers. These two offer distinct advantages over the previous types and are used thoroughly throughout industry, with many applications, from power plants, to chemical, to offshore, amongst many more.

Fire tube boilers contain many small tubes connected to a heat source. Hot gases from the heat source/fire run through the tubes and as the tubes run through a sealed container of water, thermal conduction occurs and the water is heated as it contacts the surface of the tubes. Many small tubes produce better conduction by virtue of a larger surface area.

Water tube boilers operate in a very similar fashion to fire tube boilers. They again have tubes, a water source and a heat source. The only difference is the way the sources are effectively hooked up. Water tube as the name implies run water through their tubes instead of hot gases. The tubes then run through a container containing the heat source and steam is produced in the tubes as thermal conduction occurs, and the water in the tube evaporates.

In both instances, saturated steam may then re-enter the furnace to become superheated. Superheated steam is dry and used in power stations to drive turbines. Dry steam is important here because water can damage the turbines and cause significant problems.

Imagine a scenario where damage to the superheat tubes causes steam purity to be reduced, allowing moisture to come into contact with the turbine. Over time deposits form in the turbine, slowly undermining its performance, and eventually causing a failure requiring it to be taken offline. During the downtime millions are being lost in reduced production capacity, millions are being spent on repairing the turbine, and time and energy are wasted dealing with a problem, that really shouldn't have been allowed to occur in the first place.

NDT or Non Destructive testing methods can be used to inspect the condition of the tubes, boilers, and turbine to determine if deposits are forming or any other flaws are present. Regular inspection can prevent situations like this occurring, as well as provide insight into what's happening in the system, and allow fine tuning to be performed. All at a fraction of the cost.

The cost of getting NDT work performed is often reduced as more inspections take place. Initially little is known about where or what might need inspecting. But as conditions are determined, later rounds of inspection can focus on the worst areas, and leave areas of high condition alone for a longer period of time, reducing risk amply, and also reducing cost.

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