RECOVERY BOILER STUDS

How they protect boiler tubes

Protection to the tubes in Recovery Boilers very poorly understood because it is granted in a rather complex way.

Their main goal is to promote a quick temperature drop in the smelt causing it to freeze. This frozen layer is the real insulation between the tube and the incoming aggressive agents associated with smelt.

This concept is shown in the picture below and more detailed explanation about the mechanism of protection (and collapse) of studs in Recovery Boilers is provided when you click here. Also field results confirm clearly the effectiveness of the concept, as shown in the following pictures which show the transition portion of one tube from the studded to the non studded area.

If you are responsible for a recovery boiler and need a crash course that will make you entirely comfortable to talk about studs, use this link.

Supplying and applying studs have been our core business since 1980 and we are proud to take a very different approach to deliver our services. We do not supply studs as commodities but we believe that studs are just as good as the results they deliver. With this in mind we continuously develop new ways to improve their performance, making them last longer and perform better. To better understand the way we deliver our services we suggest you to log in as "guest".

This is probably the most overlooked property granted by studs.

Each stud is a fin connected through a metallurgical bond to a tube and as such it has its temperature distribution and heat flow clearly described by mathematic formulae. Working backwards it is possible to determine to what conditions the studs have been exposed, analyzing their condition when the boiler is shut down.

As the heat flows from the stud to the tube and is carried over by the water, the stud should reach a thermal balance where each of its sections operates at reasonably well defined temperature ranges. Whenever this balanced condition is affected the change in the temperature profile leaves indelible marks in the studs. This is our tool to analyze the conditions to which the studs have been exposed.

Our crews have been trained to report all abnormal condition they encounter during our restudding operations. This has become a proven tool in the prevention of major repairs. Presently we have around 30 different circumstances considered to be abnormal and leading to the most possible cause of the problem. We will be happy to provide additional information about this feature upon request (use the enclosed form, clicking here). Submitted pictures will also be analyzed upon request. Complete set of abnormal conditions listed is available to customers with a maintenance contract.

We display below two clear examples.

Description of mechanism In case internal deposits become a significant barrier to the heat flow, the stud will continue to absorb heat and carry it to its base until the temperature gradient readjusts to this new condition. That means the metal temperature at the base will be higher than normal. As corrosion rate is also a function of temperature, the metal consumption is accelerated at the stud base.

Description of mechanism Restudding was long overdue in this case. Oscillation of smelt gun caused variable heat input in the tube, resulting in cyclical contractions and expansions on the material. Resulting cracks, rule out the tube for use in a Recovery Boiler.