New Deck Repair Material Introduced
The system comprises a polyurethane-elastomer core between two steel plates, ideal for hopper barges used in dredging, said Turner. Water lying in the bottom, and the impacts by buckets corrode away the steel in these barges, he said. When repaired or originally built with SPS, the elasticity of the material will cause an unloading bucket to rebound from the surface without damaging it, he said.
Two processes are available: the newbuilding process known as SPS, and the repair process, SPS Overlay.
SPS is a good candidate for new vessel hulls. One shipyard estimated that building a vessel using SPS reduced labor by 44 percent due to the simplicity of the process and the reduction in stiffeners needed.
An SPS hull is created in 200-square-foot sections, with two thin steel plates, separated by spacers, creating an approximate one-inch cavity between the plates. I-beams are placed on top of the plates to keep the surface flat, and a polymer developed by BASF is injected using equipment manufactured by Gusmer Corporation, Lakewood, New Jersey.
Component materials are liquid and pre-warmed in feeder tanks, with catalyst included. The polyurethane-elastomer liquids are mixed in a high-pressure injection head, and the cavities between the steel panels are filled, with an injection rate of up to 2.5 liters per second. Reactive injection molding (RIM) reaction is rapid, and "set" time (two to 15 minutes) can be tailored to meet the requirements of a specific application or situation.
The plastic swells as it sets, which raises the top steel plate slightly, while the I-beams keep the surface flat. They can be removed as soon as the material sets. The process takes about 30 minutes per section.
Benefits of the structure were confirmed by Professor Chengi Kuo, research professor and former head of the Department of Ship and Marine Technology at Strathclyde University in Glasgow, Scotland.
"(SPS) offers the industry a new material with very attractive features, many of them derived from its exceptional energy absorption qualities which, among other things, provide improved protection of the ship and its cargo in the event of a collision," he said. Other benefits are the reduced transmission of vibration, and thermal insulation qualities, which will protect machinery from damage caused by vibration forces, and improve the overall fatigue life of the hull structure, said Professor Kuo.
"The good resistance and insulation properties also make it ideal for use in partitions. It would contain fires for longer while keeping temperatures down on the unexposed side, preventing the fire's spread and facilitating safe evacuation of the area," he said.
When a vessel's surface becomes "dished" between the holders, the traditional repair has been to remove the fatigued steel and replace it, a process known in the shipbuilding industry as "rip and replace."
"We can leave the original deck there, clean it, lay a new deck on top and fill the cavity with the polymer," said Turner. "Because of the plastic core, the dishing will never happen again on that vessel," he said.
"SPS Overlay enables us to create a better deck than the original one. Because you don't have to take out the old deck, the risk associated with the project is reduced, and the repair duration is cut by over 60 percent. In a recent project for Stena Line, IE used SPS Overlay to reinstate 12,000 square meters of vehicle deck on three RoRo ferries in 60 days, saving Stena Line 140 days lost operational time," said Turner.
The company's most recent North American application was on a bulk carrier operating in the Gulf of Mexico. The original hull was ¾-inch steel, which had eroded in places to ¼ inch, said Turner. The hull was replaced with SPS Overlay and the vessel is back in service.
IE used Gusmer injection equipment on pilot projects, and its first major North American application was for the repair of two decks of the Atlantic Freighter, a RoRo ferry owned by Marine Atlantic and repaired at NewDock in St. John's, Newfoundland. The project took place in sub-zero conditions in February 2003, and involved 1,325 square meters of steel plates on two decks.
"We needed a complete injection rig placed into a 20-foot marine container that would be subjected to extreme cold and hot weather conditions," explained Turner. "Plus, we gave Gusmer very short lead time, less than two months - including the Christmas holidays."
Essentially, IE provided a metal container, which Gusmer fitted out with an RX400 Injection System from its RimCell RX Series. The modular design and flexible controls of the systems permit the installation of auxiliary components such as temperature control units, multi-station ringlines, and color dosing units.
"Gusmer met all our expectations and delivered an excellent solution," Turner said. "They sent two men up for the entire project. They wanted to learn firsthand what we were doing with their machine, so that the next machines could be built specifically to our needs. We were very impressed with their ability to meet a tight deadline delivering something they'd never done before, and with the support they gave us on the project."
"The quick turnaround and hands-on assistance we gave IE on their Newfoundland project demonstrates the level of commitment we have to supporting our customers," said Ray Lutick, a Gusmer RIM process manager. "We are a performance-driven company, and love meeting this kind of challenge for innovation and quick delivery," he said.
The SPS service is permanently established in Europe and North America, and can be arranged as needed in other countries, said Turner.
The process fits easily with existing working practices of customers and licensees around the world. The shipyard or steel fabricator is responsible for installing the steel, and IE designs the system and methodology, obtaining Class approval (e.g. Lloyd's Register), coordinating and supervising installation, and supplying and injecting the polyurethane.
The components are housed in a truck, which is dispatched to the shipyard of the customer's choice, while technicians travel in from London. On August 28, the North American truck was in New Jersey, having been in the Gulf of Mexico region two weeks before, and scheduled to be in Montreal by mid-September.
PROCESS THOROUGHLY TESTED
The process was developed in 1995, and has undergone extensive testing and evaluation through pilot restoration projects and a rollout of commercial SPS Overlay contracts.
IE was conservative about development, Turner explains, because the company wanted to seek involvement and approvals from suppliers and major regulators.
"This is the first new heavy engineering material since the introduction of steel 150 years ago," Turner explains. "We are now confident that we are offering the market a proven product."
IE has identified two distinct markets for SPS: maritime and civil engineering. Typical maritime applications include hulls, decks, and ramps, hatch covers, bulk carrier tank tops and barge inner bottoms. Civil engineering applications include bridges, rail cars, sports stadium risers and flooring systems for high-rise buildings.
The bridge market alone promises to be a burgeoning one. In the United States alone, more than 200,000 bridges have been built in the past 50 years, many with steel decks. SPS Overlay will make restoration of these decks easier and faster, and offer improved performance. With new bridges, such as the ones used for highway overpasses and longer suspension bridges, SPS offers a simpler structure that is easier to erect and, in the case of an orthotropic bridge deck, significantly reduce the amount of fatigue-sensitive welded joints.
Today, there are SPS structures on ships in service classed with Lloyd's Register of Shipping, Det Norske Veritas, American Bureau of Shipping, and Bureau Veritas. Other designs have been approved by Germanischer Lloyd and ClassNK has granted SPS approval in principle.
Licensing opportunities will be available for specialists who perform steel restoration, and others in related civilian and maritime construction industries. Training and equipment will be provided by IE, BASF and Gusmer.
For more information, contact Intelligent Engineering in London, phone +44 1753 890 575; website: www.ie-sps.com.
This article written in conjunction with Ed Sullivan, a technical writer based in Hermosa Beach, California.