A Different Perspective: Boiler Lagging: Field Procedures and Project Planning
The importance of properly installed lagging over insulation has increased a hundredfold in light of the Environmental Protection Agency’s (EPA’s) recently released Clean Power Plan (CPP). These new regulations call for a 32% cut in carbon emission by the year 2030—an increase over the reduction levels established in 2005 and the reductions proposed in 2014. This means that power plants that still use coal (currently about 70% of electricity produced in the United States) will either shut down or install additional air pollution equipment, build new gas/oil/renewable fired boilers, or convert existing boilers to burn oil, gas, or renewables (trash, wood, etc.). Since lagging is a key component to any of these options, it will take considerable planning before and during the actual work to ensure it is installed properly. It is important to remember that lagging must be installed to present a true plane and stiffened and fastened on adequate centers to prevent excessive deflection or “oil canning” so it can protect the insulation that will keep the boilers and equipment thermally and energy efficient. Lagging is a tailored and fitted application, meaning it demands twice the planning and attention compared to other components required to build or maintain a steam-generating boiler.
While any lagging project requires planning and preparation, when working on large air-pollution equipment projects or boiler conversions, each step must be considered in order to meet construction schedules. Following are some key areas of consideration.
Before any lagging work can be started, arrangements should be made to ensure a proper flow of materials from the various sources of supply. Below is a normal procedure, with estimates for the length of time needed for each stage, to accomplish the initial preparation.
- Prepare quantitative take-offs calculating the exact amount of materials required for the project—this will start as soon as all contract drawings are available and can take up to 8 weeks to complete.
- Establish project planning for an even flow of materials and work force—this should be done prior to arrival on site and before material orders are placed to help establish material requirement dates. This may take up to 2 weeks to complete.
- Make any necessary requisitions and orders for the materials—this will take up to 2 months to complete, so it is important to be aware of the time table of when the material will be required on site.
- Send all copies of the material requisitions along with copies of the detail work sheets showing all items required to the field office for the purpose of scheduling quantity release.
- Establish where the materials are to be stored and staged for an even flow of work. Determine a location that will keep them safe from damage.
- Establish the best location for the sheet metal shop* with the least transportation and handling of the materials to elevation. *A sheet metal shop will vary in size and fabrication capability in relation to the job involved. Large projects of more than 20,000 square feet will require an area of approximately 2000 square feet.
- Ensure the materials are received based on the required dates.
A typical time table for a new 600 mw radiant-power boiler including new back end and air pollution equipment is as follows: 10 weeks for the project award, including items 1 and 2 in the aforementioned list; 8 weeks for item 3; 2 weeks for items 4, 5, and 6; and finally, arriving at item 7, material receipt. As is demonstrated by this time table, the preliminary work from the time of award to the actual materials arriving on-site may take as long as 20 weeks, making proper planning essential for a well-run project.
Outer lagging is installed after the insulation has been installed. Even though lagging is the last item that needs to be installed, it needs to be part of the planning process before the insulation is installed. Pre-planning of the lagging system is essential to establish where and how the lagging attachments will be installed and will ensure the lagging attachments are installed prior to the installation of the insulation. The following steps are important in the pre-planning process.
- Start planning and layouts 3 weeks prior to the start of any insulation work by designating 1 or 2 sheet-metal workers or supervisors. This will allow enough time for the supervisors to acquaint themselves with the areas to lag, material staging, and scaffolding requirements.
- Start installing all the lagging attachments once the work areas have been released from other crafts (e.g., boilermakers).
- Field measure the complete flat-plate wall or tube-wall areas. Then cut the rib lagging to length ahead of time (do not worry about penetrations, doors, and wall boxes—these will be finished later).
- Stage your pre-cut lagging at elevation wherever possible.
- Plan on starting the installation of the rib lagging approximately 1 or 2 days behind the insulation application. (Remember to always start from left to right.)
- Field mark the location where the rib lagging will start—always from the left-hand side.
Usually, the installation of the lagging follows the sequence of the applied insulation. On outside work, it is imperative that the insulation be covered at the earliest possible time. Thus, outside work may take precedence over work located inside a building or boiler house. Following are important application considerations:
- Start installing rib sheets once an area has been insulated or approximately 1 to 2 days behind the insulation work—remember to start from the left and work to the right;
- Field cut out the rib lagging for any penetrations, doors, wall boxes, etc., staying a minimum of 4” back from all locations;
- Install rib lagging, ensuring the ribs are plumb and square (“square to the world”), and all laps pulled tight;
- Field measure the flashing and begin the fabrication and installation of the penetrations, doors, wall boxes, etc., once the area has been covered with
rib lagging; and
- Use finger-tab flashing on outdoor areas above all doors, wall boxes, and penetrations, for water shed, then caulk as required.
Finally—and equally important to the basic set up of the work, the preparation, material flow, and standardization of procedures—is work productivity. Any number of factors can affect productivity—such as accessibility, height elevation, material handling, and hours of work. Having taken all of that into account, a typical lagging crew—at elevation—first and foremost must perform at an acceptable rate to meet schedule. Once the lagging
attachments have been installed and the rib sheets have been cut to the proper length (this will be done for the most part prior to the actual installation of the work) a 2-person crew should be able to install 300 square feet, at minimum, in 1 day (approximately ten-ten foot rib sheet). Thus, the expected productivity, in many cases, should be set higher or lower based on all of the external variables, crew work experience, and the predetermined productivity to meet schedule. A typical productivity chart below is shown above.
Standardized Lagging Application Techniques
As discussed in the boiler-lagging article published in the May 2015 issue of Insulation Outlook, the standardization of lagging practices should be considered. Most lagging standards and drawings issued by the current Original Equipment Manufacturer’s (OEM’s) are based on long construction schedules with the outer flashing installed first. This is impractical in today’s more common fast-paced construction schedules, where insulation and lagging is pushed to the very back of the schedule or squeezed into an unacceptable time frame. In the aftermath of the new EPA rules, the need for standardization of application procedures is becoming more crucial. All sectors of the power industry will be trying to reduce cost, which sometimes affects quality. It will benefit the boiler industry to establish consistent lagging applications, regardless of the area of the country the work are being done.
The success or failure of implementing such procedures and standards will also depend on the basic setup of the work, the depth of the preparation, and the ability of the shop or fabrication crew to keep material flowing to elevation. Under normal job conditions, a shop crew of 2 workers can keep material flowing for 2 or 3 different application crews. On the larger projects of more than 10,000 square feet, the shop crew size must be increased according to the number of installation crews to ensure a completely efficient operation.
Having a set of established standards will also ensure that the lagging and flashing will be installed the same no matter what floor, elevation, or location of the boiler, and regardless of different crews.
All lagging projects require planning and preparation that will ultimately protect the insulation, which provides a thermal and energy efficient steam-generating boiler. Additionally, the steam-generating boiler industry would benefit greatly if lagging standards, practices, and procedures could be established. These standards would help streamline all the planning that a properly installed lagging system requires before and during the actual work. The importance of these standards will become increasingly apparent for the entire steam and power industry and the companies that provide services and materials to these industries as the CPP comes into effect.