By Andjelko Piskuric
Whether it is new construction or replacing equipment during an outage, today’s power plant construction projects place great emphasis on safety, on-time delivery, and budget. No matter the size or scope, these projects require a great deal of pre-planning and coordination in order to execute well and deliver these results. One type of construction practice, modular construction, can enable greater success in meeting these objectives.
Modular construction consists of fabricating and pre-assembling equipment in a shop environment, then shipping these sub-assemblies to the construction site via rail, barge, or truck. Once delivered to the jobsite, these sub-assemblies are bolted or welded together, to form the final piece of equipment. This is in contrast to traditional construction practices that involved shipping pieces of steel, fiberglass, or other materials to site, where they were fabricated and assembled one piece at a time.
Modular construction is not a new process. Other industries have been applying it for decades. For example, homebuilders have been pre-assembling walls and trusses in the factory, instead of shipping bundles of un-fabricated lumber to the home site. This type of process is being applied to power plant equipment like heat recovery steam generators (HRSGs), cooling towers, turbines, boilers, air cooled condensers (ACCs), transformers, and other equipment. It could also include components like stairways, conveyors, piping, electrical and control systems. Several EPCs are leading the modularization effort, and have built power plants with this type of approach. Modular construction is a common practice found in other parts of the world, and has been slowly adopted in the US. There are many benefits to this type of construction practice, but it also introduces some challenges.
|Modular construction requires less manpower, because there are fewer construction activities that need to be performed on site. Photo courtesy: SPX Cooling Technologies|
It has been well-publicized that fewer people are entering into the skilled trades. That is resulting in challenges with staffing a large project, especially those that are located in remote rural areas where power plants are often located. The labor challenges are further strained, if there are multiple contractors on site that require the same skilled trades, and are competing for the same resources. A lack of experienced craft workers creates further challenges. Modular construction requires less manpower, because there are fewer construction activities that need to be performed on site. Also, the nature of the work that is performed on site is different. It greatly reduces the amount of craftsmanship involved with installing a piece of equipment, and replaces it with assembly type work.
Having less labor and fewer activities on site translates into an additional benefit of decreasing the risk of a safety incident. Any work that can be performed at the ground level will be safer and more efficient than doing aerial work where fall protection is required. Modular components are larger and heavier, so safety risks do still exist while handling the equipment. However, there is less cutting, welding, and grinding on site, which are all leading causes of work related injuries.
Modular construction compresses the overall project schedule, since there are fewer activities that need to be performed on site. This can be very advantageous at a busy construction site. It enables other construction activities to start sooner, or be scheduled in parallel, thereby reducing the critical path for completion. Modular construction also reduces schedule variability, since there are fewer construction activities on site. All of this leads to a greater likelihood of meeting the contractual schedule completion dates.
Anyone that has ever been to a power plant construction site knows that space is limited, and having adequate lay down space for material is a challenge. Traditionally, material is delivered to the job site in advance, and stored near the work area. Having materials close to the work area is critical to maintaining productivity. In the staging area, the material is spread out and sorted to find the right items needed for a specific task. This requires lay down space for the duration of the activity, which could be an extended period of time. In contrast, modular components are delivered on a just-in-time basis. This eliminates time spent sorting through materials in storage. In many cases, modular components are picked directly from the truck and placed in their final position, thereby minimizing the need for lay down space. This results in a more organized and productive jobsite because it alleviates site congestion and enables other construction activities to proceed.
Modular construction is of consistently high quality, since the work is performed in a controlled factory setting by experienced employees using automation for fabrication. Any errors or issues that arise during production can be quickly identified and corrected. These sub-assemblies can be stored at the factory and inspected by the customer beforehand. Conducting factory acceptance tests can expedite the inspection and approval process, and further compress the schedule.
The weather can be both a benefit and a challenge for modular construction, especially if the equipment is located outdoors. Since there are fewer construction activities that need to be performed on site, it means that the overall schedule is less susceptible to weather. This is particularly favorable in periods of cold or wet weather. Windy or severe weather, however, can still pose a challenge. When wind speeds exceed 25 mph, it is not advisable to hoist loads with a crane since the wind gusts could shift the load and create safety hazards. Similarly, severe weather or lightning could force all construction activity on site to stop.
|The freight cost to transport modular components, which are heavier and potentially oversized, is a significant factor to consider. Photo courtesy: SPX Cooling Technologies|
Before any component is modularized, it must first be designed for this type of construction practice. In addition to designing for the specific project requirements such as wind load, snow load, and seismic conditions, these sub-assemblies must be pre-engineered for this type of installation. The equipment must be designed into segments, so that it can packaged for shipment. These segments may require additional reinforcement at specified pick points, so that they can be rigged and hoisted at the factory and on site. The size and weight of the sub-assemblies are important factors to consider. The equipment needs to be sized so that it can be handled in the factory and onsite. The weight and overall dimensions are also critical for transport and for handling by the crane. The modular sub-assemblies may require additional braces to stabilize the segments during handling and transport. They may also require additional structural elements to meet stability requirements and achieve robustness. A rigging and crane lift plan should be developed with Engineering, so that the work can be performed safely.
Modular construction is highly dependent on delivering components on a just-in-time basis. When multiple shipments are needed, this requires extensive pre-planning and adherence to a schedule. It also requires coordination between the factory and site. The sub-assemblies need to be delivered in the right sequence and at the right time. That means that any construction activities that must be performed in advance, must be completed on time or the entire schedule will be impacted. It also requires coordination with the EPC or Plant Operator on site, since there could be multiple deliveries by other contractors which could lead to site congestion and delays.
Some of the biggest challenges to modular construction pertain to site conditions. It is critical for the site conditions to be prepared to accept deliveries of modular components. This means that the access roads leading into the plant are unobstructed, clear of other construction activities, and prepared for truck traffic. The roadways must be compacted and graveled to enable passage of a heavy truck. This could be a challenge if rain turns the roads into muddy sinkholes. The heavy truck will find the roads impassable, which could lead to site congestion and delays. The plant access roads also need to be wide enough to accommodate oversized loads if necessary, and accommodate trucks that need to turn and maneuver into position.
Having access for the crane is also critical. The crane needs to be placed adjacent to the work site, so that components can be offloaded and installed in their final position. Here too, the area needs to be compacted and graveled so that the crane is on solid footing. If crane access is not possible, then larger cranes with a longer reach are needed to pick and place the equipment. While this is possible, larger cranes do add cost to the project.
The costs for modular construction are highly dependent on several factors, and these can determine if the overall cost is greater than or less than traditional build. The breakdown of these costs will vary by type of equipment, manufacturer, and location, but here is a general overview.
The material costs for modular construction could be marginally higher, since additional material may be needed to engineer the sub-assemblies as mentioned above. The labor costs to fabricate these modular sub-assemblies in the shop will vary by equipment manufacturer, and is dependent on shop labor rates. The savings depends on the difference between the shop labor rates and field labor rates. The greater the difference, the more savings for modular construction.
The freight cost to transport modular components is a significant factor to consider, especially if there are multiple shipments. The freight cost is highly dependent on the distance to the job site, mode of transport, and number of shipments. The cost per truck to ship pre-assembled components is often greater than shipping just raw material because the loads are heavier and potentially oversized. Transporting oversized loads introduces many challenges and costs. The regulations vary by state, so it is important to check with each state’s Department of Transportation (DOT) to ensure that the shipment is in compliance.
Additional permits may be required for oversized loads depending on the dimensions. An escort for the trailer may be required for loads exceeding 12ft or more (varies by state). Oversized loads can only be hauled on routes that have been pre-established with the DOT, and must abide by blackout times and days. Also, oversized loads cannot be shipped via rail or intermodal transport.
Loads that are extremely heavy or tall cannot be hauled by conventional trailers, and require specialized Heavy Haul trailers, or low boy trailers. There are fewer trucking companies with specialized trailers, so costs for that type of equipment will be greater than standard 48ft flatbeds. While barge transport can be used to haul large heavy loads, it is limited to where it can be applied. Many plants are located inland, and are not accessible by barge.
At the job site, a compressed schedule should result in a reduction of overhead costs for site supervision, administration, construction trailers, and equipment rental. Since there are fewer construction activities that need to be performed on site, it should also result in a reduction of direct labor costs. It is important to consider the size of equipment like forklifts and cranes. Although there may be fewer components to handle with modular construction, the components will be larger and heavier. Therefore, larger forklifts and cranes may be needed, which could be a significant expense.
The costs for material, shop labor, and freight are all predictable and manageable. The cost for field installation introduces the greatest risk, regardless of whether it is constructed in traditional or modular fashion. Modular construction can minimize that risk, but variability is still possible.
Modular construction practices can dramatically improve efficiency in new construction or outage projects. It addresses today’s construction needs and results in many benefits for the original equipment manufacturer (OEM), EPC, and power plant operators, but it also introduces some challenges. Understanding the benefits and challenges enables the entire team to plan for them upfront. This pre-planning effort is critical for the project to succeed.
Andjelko Piskuric is a Sr. Global Product Manager with SPX Cooling Technologies.