“The method of Plant Design which enables fabrication and assembly of a large proportion of the plant to take place in a location remote from the project site.”
Modules and Pre-Assembled Units (PAUs) typically consist of equipment items arranged in modular steel structures that can be assembled off-site, transported to site and lifted into place. The equipment is connected with piping to the fullest practical extent, instrumentation is installed and cabled to junction boxes, lighting and cabling is installed, steelwork is fireproofed up to the connection points, tracing and insulation on equipment and piping, and painting is completed as far as practical.
There are typically four categories or concepts of modularization applied:
PAU/PAM (Pre-Assembled Units/Modules)
PAR (Pre-Assembled Racks)
VAU (Vendor Assembled Unit)
VPU (Vendor Packaged Unit)
The following sections focus on pre-assembled modules and pre-assembled racks as they best demonstrate the value offered by tkIS with its proven planning, design, logistics, hook-up and commissioning processes.
Opportunities for modularization are assessed at the outset of every project. tkIS personnel work with our Clients to evaluate their needs, the project's size, the installation site, and other factors to identify the most appropriate construction option.
Most large projects allow for some modularization and a combination of modular and stick-build construction is identified as the most effective in the majority of cases.
Typical difference between conventional and modular layout.
Advantages of Modularization
Improved safety due to the workshop environment and reduced requirements to work at height
Reduction in Industrial Relations risk
Reduction in the site work force
Improvement in schedule due to opening up multiple work-fronts and minimized impact of weather
Increased efficiency of labor and equipment
Lower labor costs in workshops
Improved quality control
Potential for testing and some pre-commissioning prior to delivery to site
Drivers for Modularization
Inaccessibility of the site such as offshore oil/gas platforms
Remote site location
Schedule improvement, particularly if a short time is available for project implementation
Limited availability of construction workforce
Industrial relations issues
High cost of construction workforce at site
Impact on local community and infrastructure
Improved Risk Management
Typically modules are complete plant assemblies weighing 100 tons and above. PAUs are similar to modules but smaller, typically weighing up to 100 tons. In addition to modules containing equipment, the inter-connecting pipe-racks in the plant can also be modularized. The various types of module and PAU for consideration are:
Large Complex Modules
The size and scope of these modules are only limited by the physical constraints of the transportation route to the site location and the available capacity of heavy-lift and transportation equipment.
Modules for offshore projects usually fall into this category. Onshore modules can typically range up to 5,000 tons, although the maximum practicable size and weight will vary from project to project. The use of large modules for onshore plants usually requires the site to be on or near the coast with direct ship access.
Modules with Transportation Limitation
Where the site does not have deep-water access, significant land or canal transportation of the modules will be required. In these cases, the module size will be limited by the restrictions of the transportation method.
A preliminary transportation study, undertaken during the feasibility stage, is essential for these projects.
The extent of modularization should include the project buildings. Consideration should be given to control-rooms, amenities buildings, sub-stations, switch-rooms and instrument rooms being fully pre-assembled and fitted-out off-site. The size of these modules could range from shipping containers through to complex buildings consisting of several modular sections.
Consideration should also be given to pre-assembly of sections of steel buildings, either off-site or on-site at ground level to be lifted into place in sections.
The figure below shows the 3D model and the final installation of a section of plant made up of stacked interconnected modules. The colors in the 3D model view indicate the individual modules, with the dimensions of these modules set by the transportation envelope. The modules would be trial-assembled in the module yard and interconnecting piping installed and match-marked. After testing, the various modules will be separated for shipping.
Modules for Brownfield Projects
In cases where major sections of plant are required to be installed in an existing unit during a short shutdown window, consideration should be given to modularizing these sections of plant and building the modules on the site within lifting or hauling distance of the final location. Module assembly would then take place with the existing unit in operation, with only the lifts, final connections and hook-ups to the modules to be completed during the shutdown period. The size of these modules would be limited by the heavy lift capacity or the hauling design. The photograph shows a large modularized plant section that has been assembled on site for installation during a shutdown.
Modularized Vendor Packaged Equipment
Equipment specifications should define that equipment should be modularized as far as possible by the vendor. This should include aspects such as rotating equipment and drivers mounted on baseplates, lube-oil systems delivered complete on skids, air compressors and dryers on skids with valving installed.
Complex packages such as PSA Units and TEG Units should also be specified as modular construction with minimum site-work required.
Major equipment such as reformers and convection banks should be designed in modular sections for ease of installation.
The design of major rotating equipment, such as steam-turbine driven compressors, could consider the use of a modular approach, where the vendor delivery would include part of the concrete table top with equipment, piping and I/E pre-installed.
In addition to the modularized sections of plant described above, consideration is given during the design to minor pre-assemblies that could minimize work at the site. Examples of these are:
Pre-cast concrete foundations and plinths
Use of pre-cast concrete for table-tops
Use of pre-cast columns socketed and grouted into pre-cast pockets in foundation slabs. This approach could be applicable to columns under reformer boxes and pipe-rack columns that require passive fire protection
Sub-assemblies – stairways, ladders and trusses
Pipe assemblies at control valves, pressure relief valves and pump sets
Steam trap and drain hook-ups
The use of pre-cast sections and other pre-assemblies can be particularly applicable for Brownfields projects where construction access to the operating plant will be limited. A typical example of a pre-cast concrete table top is shown on the right.
The application of the modularization philosophy for a Project must form part of the overall Project planning, execution and risk management processes. Typically, we see the key benefits to include improvements in quality and productivity, cost savings from workshop costs vs site costs, schedule improvements and mitigations of site risk, especially via HSE performance and Industrial Relations performance.
Modular construction offers many advantages over the conventional "stick build" methodology of construction. With the majority of the fabrication and assembly works performed at facilities remote from the Construction site, this allows us to ensure all work is performed according to our high standards, under controlled working conditions.
Also, by reducing field exposure hours, we also minimize the project's impact on the customer site, a significant advantage when the installation site is an operating plant. Modular construction also minimizes lay-down space, an important benefit when the field site is small or congested, and reduces delays due to adverse weather. In-air work is minimized, and foundation requirements are often simplified.
Requirements for highly skilled labor onsite are minimized, an advantage in areas where skilled labor is either costly or unavailable. Procurement is often simplified, especially when the installation site is located in an area where raw materials and equipment are expensive or difficult to obtain.
In addition, modular construction can shorten schedules by allowing for concurrent processes, such as fabrication, permitting and logistical arrangements.