Home News & Events Tube water wall overlay at American Electric Power, Conesville, Ohio – March, 2015

Tube water wall overlay at American Electric Power, Conesville, Ohio – March, 2015

Jul. 20, 2015

The inside walls in the boiler of a coal fired electric generating plant face tremendous thermal and physical loads during operation. These walls are made up of a series of tubes, typically 2 to 3 inches in outside diameter, standing side by side vertically and connected by narrow sections of thin plate called a membrane. Water runs within these tubes and is heated by the burning coal within the boiler. The water is super-heated to steam and is then run through a turbine which, in turn, spins a generator that creates the electricity you use in your homes and businesses. 

 

 
 

 

The coal to be burnt is first pulverized into a fine, powder-like consistency. It is then blown into the boiler where it swirls about and burns. This swirling fire generates wear which thins the walls of the internal faces of the tubes within the boiler. If left un-checked, the tube walls will become thin enough to allow the highly pressurized water to leak, which reduces efficiency, increases operating costs and can cause forced outages which is a complete shutdown of the generating unit. This results in a reduction in the operational life of the boiler and perhaps even the generating plant itself.  

 

Extending the operational life of the boiler makes good economic sense. In order to do so, the walls of the tubes in the boiler must be brought back to their minimum allowable wall thickness. This can be done by fully replacing the tubes themselves which involves cutting out sections of the tube wall and replacing either individual tubes or whole sections of the wall. This solution is necessary if the tube walls have become so thin as to allow leakage. However, if the degradation of the tube wall thickness can be determined before this minimum value is reached; it is possible to restore the minimum wall thickness by means of welding a layer of material over the present surface.  

 

Overlay welding of boiler tube walls has been successfully applied for quite a few years. Typically, the operation is contracted out to a company that specializes in this work. In this case, the company brings in their proprietary equipment and welding operators and performs the welding. This approach leaves all responsibility for the success or failure of the weld overlay project on the contractor company but it often results in a very high cost relative to the overall project and also reduces the number of tradesmen employed from the local work force.

 

The American Electric Power, Conesville Generating Station took a different approach for their recent scheduled outage. Rather than hiring a specialized overlay welding company, the maintenance team, lead by Bill Buzzard and Steve Louderback at Conesville, worked with Skanska USA, a world-wide construction management company, to handle the overlay welding in-house. Tony McQuay with Skanska began research regarding equipment available to perform this operation. Tony contacted his local Bug-O Representative, Mark Campbell, and the Overlay System from Bug-O Systems was determined to be a practical solution. Further communication occurred as the Bug-O Technical Support Group was contacted and a demonstration was scheduled.  
Persons from AEP and Skanska traveled to the Bug-O demonstration/training facility in Canonsburg, PA for the demonstration. AEP brought along a section of the tube wall and a series of test welds were made. After a few trials it was quickly understood by the team from AEP and Skanska that the Bug-O Overlay System provided a very good solution for their application. The process of quoting and system refinement was undertaken and an order was placed for one complete system.  

 
   
As with any new approach to a project, it is the people involved who can make or break the overall success. In this case, the Boilermakers with Local 744 out of Cleveland, Ohio were the individuals who made this project a success. Shortly after the order was placed, AEP worked with the members of Local 744 to come to the demonstration/training facility at Bug-O for a series of training courses in the assembly, disassembly, set-up and operation of the Bug-O Overlay System. This training was later reinforced at the Conesville site where AEP undertook the fabricating of a test fixture that allowed each of the Boilermakers to make many practice welds with the system in full operation. This test fixture allowed a section of tube wall to be mounted and placed in either the vertical or sloped position to accurately mimic the conditions in the boiler. Tasks that originally appeared complicated and troublesome were simplified and learned prior to taking the system into the boiler and putting into operation. While in the training facility, each Boilermaker was qualified on the welding procedure and the operation of the equipment. Without question, the opportunity for each of the Boilermakers to become familiar with the operation and set-up of the system was crucial to the success experienced once the actual outage was underway.  
   

After scaffolding was placed inside the boiler and the interior surface of the boiler was sand blasted to remove residue, the Overlay System was put in place on the tube walls. A series of angle brackets fabricated by the AEP staff was welded onto the face of the membranes between the tubes. The Aluminum Rigid Rails that support the system were then bolted to these angles. This provided a very solid base for the moving portions of the system. The horizontal and vertical travel sections of the system were then installed on the rails. Finally, the welding equipment was mounted to the travel carriages so that the weld process could be performed. Due to the familiarity provided in training, the set-up of the system was performed relatively quickly. In order to be prepared if any unforeseen problems were to arise during this initial start-up Bug-O Applications Technician, Isaac Guest, was placed on-site for the first few days of the operation. As one might expect, some minor issues did occur but they were quickly resolved with Isaac’s help. The welding process was started and initial evaluation was undertaken.

 

The initial plan by the AEP team was to install and begin use of the first system and determine if it would be satisfactory. If it was determined that the operation was not going as well as planned, the equipment would be removed and additional Boilermakers would be brought on-site to perform the welding by hand. In fact, it was determined that the Bug-O Overlay System was performing very well and that it would be wise to purchase a second system to make the operation go even quicker. A rapid response by the manufacturing group at Bug-O in Canonsburg provided a second system to be in place and operational in only a few days.  

 

Bill Buzzard with AEP said this, “On the question regarding time, by purchasing the second machine we were able to finish about a month early. We were averaging between 10-12 sq. ft. per machine per 10 hour shift. I think we can do a little better by improving our process and a few tweaks here and there. I have been running some numbers on our savings of doing it ourselves vs. hiring an outside company, the numbers look really good.”

 

 
Some issues with the welding process and process equipment were experienced but these were quickly diagnosed by the Boilermakers and resolved. Problems with wire feed and material still residing on the faces of the tubes resulted in some delays but they were all considered to be minor and were worked around. Further, the crews operating the equipment began to understand that the Bug-O equipment was built well and was robust enough for this environment. The Bug-O Technical Support and Engineering Groups received extremely valuable feedback regarding the controls and functionality of the product in this challenging work space. All of the challenges presented during the welding process taught the crews from Local 744 and the maintenance team at Conesville that time spent in preparation result in big gains in productivity during the actual welding of the tube faces.   
 
The overall outcome of this project was a resounding success. It was determined that there is a definite financial advantage for the generating station to purchase their own overlay motion control equipment and hire local labor to perform the operation. This project proves to be a win – win situation. Local labor gets more members working on the project; AEP saves money and time during the outage. Onsite support and direction by the local Bug-O representation, Mark Campbell and Bug-O Technical Support Group and Engineering Group in Canonsburg, PA proved to be essential to the final realization of this endeavor.  
 
It cannot be stressed enough that the success of this project was a result of a true team effort. Thank you to the maintenance team at AEP and the outstanding union labor from Local 744 for a job well done.