SAGE SMART STUD PROTECTION IN RECOVERY BOILERS

1. Mechanism

Studs in Recovery Boilers must promote a quick cooling of the smelt in order to "freeze" it and thus form a solidified layer on the tube wall.  This layer insulates the tube surface against incoming smelt/black liquor droplets.

As long as the mass of studs and their metal bond to the tube are properly sized and provided the heat conductivity of the studs is right, the process is absolutely reliable.

2. Associated Problems

The above described mechanism works well until the studs require replacement.

As they wear off, studs will assume a conical or bullet shape profile depending upon several variables which are mentioned below.

These undesirable shapes make restoring studs to the original conditions almost impossible due to the time limitations and quantities involved in the repair.

Under ideal circumstances studs prepared for replacement should be ground flat to ensure total contact between the original and new stud.

The time required to accomplish just this operation can hardly be afforded by most mills.

Unfortunately the option for not doing a proper repair results in exposing tubes to conditions that cause premature panel replacement.

3. How does the wear take place?

Studs collect heat through their total area therefore this heat collected depends on the stud diameter AND length. The heat transferred from the stud to the tube flows through the stud area bonded to the tube, therefore it depends only on the diameter.

The relationship between stud length and its diameter is therefore critical to prevent the heat collected at the stud tip from exceeding the amount which can flow through the stud base.

The further the deviation from the ideal dimensions, the sharper the resulting cone becomes.

Premature restudding may therefore affect this balance and cause harm to the boiler instead of protecting it.

Even under ideal conditions, the stud tips remain exposed to an unbalanced condition where they collect heat from above and from their sides.

For that reason the edges are always overheated and collapse first, changing the stud shape into a cone.

The graph below depicts this condition and at right one can see real field results

4. Solution = Sage Smart Stud™

In order to effectively solve the problem posed by the cumbersome interface between new and used stud, we designed a stud that can be applied on most worn studs without requiring grinding. Furthermore it wears out in such a manner that in the future its tip will be ready for another repair without requiring surface preparation. This solution is called the Sage Smart Stud ™ .

Sage Smart Studs ™ have a Chromium diffused "skin" engineered to grant a friendly wear pattern, which will easily enable complete restoration of the original stud condition when restudding is required. The picture below at right shows a typical wear pattern for our Smart Studs compared to regular studs. The only surface preparation done for the Sage Smart Stud ™ was a mild sand blasting for a clean weld.

5. Results

This new development by Sage of America, addresses the dimensional issue in relationship to the heat input and also the material corrosion resistance at high temperatures.  Differential chromizing besides ensuring longer life to the stud results in a wear pattern which allows complete reshaping of the studs when the time for restudding comes.

Pictures below show field results.

6. Availability

Ideally panels should be studded with Sage Smart Studs as they are manufactured.  Sage provides panels studded with Sage Smart Studs with service warranty at fixed price for the duration specified by the user.   If the user has a preference for any specific OEM we will be happy to apply our studs on panels provided by the preferred boiler manufacturer.

7. Repair of panels in operation

Panels already in operation can be serviced with specially engineered equipment and tools to be gradually converted and enjoy the same benefit.  A typical warranty for replacement studs applied in the boiler is 5 years.

Sage has performed repair services in many countries for 20 years and is ready to service your boiler no matter where it is. One of the major steps implemented to grant good contact area between the original and the new stud, is the nipping machine we developed which grant a clean cut of the stud without risking to scratch adjoining tubes.

For more information please email us info@sageofamerica.com