Modular transporters for modular construction21 March 2007
Engineers are using modular construction techniques on projects where space, time, or available labour is limited. However, the technique requires the use of special transport vehicles capable of positioning immense loads with millimetre precision. Will North reports
Traditionally, onshore oil and gas processing plants have been ‘stick built’; that is, they have been fabricated on site, a piece at a time. In the 1970s, however, engineers working on offshore projects developed techniques of modularisation, which saw huge pieces of equipment built on land at fabricators’ yards and then carried to their location on barges. Since the mid-1980s, these techniques have begun to be used in a new way for onshore projects.
Colin Smith, project director for Foster Wheeler Energy Limited, explains, “Modularisation in the offshore industry has always been driven by the need to combine as much equipment as possible before delivery to the site, as you have no infrastructure at the site. At the same time, using barges, you can transport very heavy loads relatively easily, with a high degree of manoeuvrability, and you have sufficient space to erect such structures offshore.”
Smith continues, “At that time [the late 1970s and early 1980s] in the onshore industry, one didn’t have the drivers of limited space and relatively high cost, and one didn’t have the flexible crane, lifting and transport equipment needed for heavy module movement.”
As the special transport industry developed new ways of moving heavy loads, it became possible bring these techniques onshore. Foster Wheeler construction engineering manager Doug Lee says, “The biggest impact on the growth of modularisation on onshore projects (from an equipment point of view) is the growth of SPMTs (self-propelled modular transporters), the first of which was developed by Econofreight in the mid-eighties. Positioning to close tolerances on a foundation is a key issue. Prior to having SPMTs, we had to skid modules into position, which isn’t as accurate and takes more space. You can manoeuvre an SPMT within tolerances of millimetres, and rotate it through 360° using carousel steering. Onshore, usually you have to negotiate roadways and corridors of access through the site. The time we can save, and our ability to move modules through the site without removing objects, is really worthwhile to the project.”
Scheuerle sales director Bernd Schwengsbier describes an SPMT: “Scheuerle SPMTs consist of a power pack unit, containing an engine with a hydraulic pump. These are separate from the transporter, so they can be connected directly or at a distance using hydraulic connectors. They use a 350kW Mercedes engine. The transmission is a hydrostatic drive system.”
In the hydrostatic drive systems used by SPMTs, the engine powers a hydrostatic pump. A series of hydraulic connectors links the power pack unit (PPU) to the individual SPMTs, where a motor converts the fluid flow back into rotational movement. This means that power can be transmitted from the PPU to many transporter modules, and that the entire compound of linked transporters can be moved to very fine tolerances, without the gearshifts of a mechanical transmission. When the operator wants to reverse the machine, the hydraulic flow is reversed.
The suspension for each axle is also linked to the hydraulic system, allowing the SPMTs to be raised and lowered. When the SPMT needs to cross an obstacle, such as a ramp, the PPU can be raised at an angle, to increase it's clearance. The suspension can keep the entire SPMT level, with axles raising and lowering as they cross the obstacle.
Steering is computer controlled, with a range of steering programs, and powered by the hydraulics from the PPU. These can include transversal drive, with the SPMT turning more at one end than the other, circular or carousel drive, with the SPMT turning on a point, or other variants with the SPMT turning on a point at, say, the front left axle.
Horst Haefele, sales director for Goldhofer, says, “The transporters are coupled together by means of a hydraulic lashing coupling system located at each end of the modules based on the same bending moment as the frame work. We offer 4, 6 and 8 axle modules to adjust the capacity and loading platform necessary to adjust it to the need of the various cargos.”
Lee says, “It is the ability to configure them into a multiple arrangement, of maybe 100 or 200 axle lines, that makes them so attractive—we always use them linked together like this.” By arranging the four- to eight-axle SPMTs into compounds with, potentially, hundreds of axle lines, vast loads can be carried. Lee says, “We believe you could go up to 10,000t. The real limit on module size is at the fabricator’s yard, in particular in their ability to load out the modules.”
These compounds can then be controlled by a single operator. Schwengsbier says, “The compound can be controlled using a wireless or cable remote control. The remote uses joysticks, giving the operator proportional control of acceleration and deceleration, lifting and lowering, as well as steering. It features a range of steering options, such as 360° carousel steering.”
As well as precision on site, using SPMTs means that there are no restrictions on where the module is fabricated, or where the finished plant is built. Schwengsbier says, “Using a rubber-tyred system like this, means that the fabricators yard can be anywhere, and you don’t need to have rails available to carry the module from the yard to the barge. At the construction site, the module can be carried on ice roads, gravel, or side roads.”
With the development of SPMTs in the 1980s, companies like Foster Wheeler were able to plan modular projects for onshore processing plants. Colin Smith says, “In our industry, ‘modular’ construction is the technique where you fabricate a steel-framed box, with all equipment and bulk materials in place. In offshore construction the scale of modularisation is far more extensive than in onshore projects due to the significant cost differential between work onshore and offshore.”
Doug Lee adds, “Foster Wheeler’s first involvement was in the eighties, on a Scandinavian project comprising over 200 modules, the heaviest of which was about 1,000 tonnes. The average onshore module—a pipe rack—weighs about 250t–300t, and is about 8m wide by 30m long. We recently constructed a 1,800t module, but most modules are in the range up to 400t.”
Modular construction has come to account for about 10-15% of Foster-Wheeler’s business, Lee estimates. But it does come at a cost. Lee says, “On grassroots projects, when comparing modularisation with stick-built methods, we would anticipate modularisation as being typically 10-15% more costly. The additional costs are due to additional engineering, additional steelwork, and increase in shipping costs.”
Smith adds, “This is where you have to look at site specifics. On an open site with plenty of space to work and available labour, modularisation would be expected to cost more than a traditional stick-build approach. But, taking one of our projects as an example, we worked on a fully developed island, Pulau Ayer Chawan, Singapore. We had a choice to either extend the island, or to ship everything-the workforce and all the equipment-in and out every day.
Smith continues, “We chose to reclaim land for the permanent works, but adopt a modular design and construction approach. This meant that we did not need to reclaim further land for temporary structures while the project was being constructed. This allowed the modules to be fabricated in Indonesia in parallel with the site works taking place in Singapore.”
Limited space is not the only factor in choosing to use modular construction. As Smith explains, labour shortages are also an issue. “Since 2004, the process plants industry has seen an increased interest in modularisation. In a number of regions, the processing construction activity has recently reached a stage where the workforce is fully engaged. The current amount of work in the process industry means there is more of a driver to make maximum use of the workforce and time on site and also to find other areas where labour may be more readily available, or lower in cost, to which the work can be reassigned.”
Smith continues, “For example, on a modular project in New Caledonia (a French overseas territorial community about 1,500 km east of Australia) there was a limited workforce on the island. Several large projects are like this - they are close to natural resources, but are far away from large population centres and have low indigenous populations.
“Another example is in Western Australia, where Foster Wheeler is adding a fifth liquefaction train to the Woodside-operated North West Shelf LNG complex at Karratha, the number and scale of in-country projects led to labour and resource challenges to project schedules and budgets. “ These pressures were a catalyst for adopting a modular approach. This allowed Foster Wheeler to distribute the project across the wider industrial market throughout the Australasian region, where available capacity could accommodate the work within the project’s required timeframes. Smith says, “This is the first onshore liquefaction train in the world to be constructed in modular form.”
While modularisation stayed at a constant rate for many years, recent years have seen a surge in interest. Recent years have seen an increase in plant revamps. At the same time, Jeff Latture of Barnhart Crane, in the USA, told Cranes Today that his firm had seen refining picking up, with a lot of major upgrades. Schedule and cost pressures have led to an increase in demand for modular construction in his area.
Foster Wheeler’s Colin Smith says, “In revamps, you’re extracting equipment and replacing it in a confined, permit-restricted, space. There are additional risks from working near adjacent facilities, while they are still operating. Transferring man-hours off site means that that you reduce your exposure to the operational regulations that apply at an operational facility. This effectively reduces the total costs.”
With modularised projects taking place around the world, the supply of trailers could itself be an issue. Smith says, “So far, we haven’t had to seek out new trailers. Over the next five years though, if demand continues as it has since 2005, we will be looking at availability.”
The SPMT manufacturers have designed their trailers with the need to make the most of a fleet in mind. Scheuerle’s Schwengsbier says, “The biggest advantage of Scheuerle’s SPMTs is that they are 8ft (2.5m) wide. This means that they can be containerised and transported around the world. For the biggest modules, a special transport company could bring SPMT units from, say, Sakhalin and Alaska, combine them, and then send them back once the job is done.”
Foster Wheeler is currently adding a fifth liquefaction train to the Woodside-operated North West Shelf LNG complex at Karratha in Western Australia - some of the modules being transported to the site. Courtesy: Foster Wheeler/Woodside. FW Woodside 1 Foster Wheeler is currently adding a fifth liquefaction train to the Woodside-operated North West Shelf LNG complex at Karratha in Western Australia - some of the modules being transported to the site. Courtesy: Foster Wheeler/Woodside. Foster Wheeler Woodside Foster Wheeler is currently adding a fifth liquefaction train to the Woodside-operated North West Shelf LNG complex at Karratha in Western Australia - some of the modules being transported to the site. Courtesy: Foster Wheeler/Woodside. Foster Wheeler Woodside 2 A Scheuerle SPMT, owned by Abnormal Load Engineering ALE scheuerle SMPT A 28 axle Goldhofer PST-SLE SPMT. The PPU at the front is connected to the six SPMT units using hydraulic connectors. PST-SLE