Case Study: Challenges With Ultra High Pressure Water Jet Re-Coat Projects
Gregg Lowes, Industrial Account Manager at Munters Moisture Control Services (MCS) wieghs in on how to properly dry two Ocean-Going Potash Conveyors at Neptune Terminals, Vancouver Harbor
Temporary climate control is becoming a regular part of blasting and coating operations throughout industry. Its ability to create improved coatings conditions while providing cost savings and quality workmanship to the owner and contractor is lending itself to becoming a popular method.
Industrial blasting and coating jobs require suitable weather conditions and appropriate temperatures and dry air. Increasing the moisture load by blasting through ultra high pressure water jetting makes controlling the environment even more challenging. Without proper climate control, humidity and dew point levels can potentially wreak havoc on plans to complete such tasks. Such was the challenge faced by Neptune Bulk Terminals Ltd. of Vancouver British Columbia.
Neptune Bulk Terminals Ltd. was established in 1967 on the North Shore of the Port of Vancouver's inner harbour. In its first year of business, Neptune handled more than 3.2 million tons of product. Since then, the terminal has grown in capacity capable of handling over 11 million tons per year. The terminal has an annual throughput capability in excess of 17 million metric tons.
Neptune features a dedicated coal berth, two dry bulk berths, bulk liquid capability over two of three berths, storage for coal, potash, agricultural products and canola oil and site area of 71 acres plus waterlots. Commodities handled include coal, potash, fertilizers, canola oil and agricultural products.
Neptune executives sought to blast and coat two large ocean-going potash loading conveyors within a 27-day window to prevent interruption of international ship loading schedules. The industrial painting contractor, Certified Coating Specialists (CCS), having successfully completed two coal ship loaders in previous years, was asked to conduct the work on the potash loaders.
The Moisture Control Services (MCS) division of Munters was asked to bid on the project, and succeeded in securing the climate control portion of the work. MCS is North America’s largest temporary humidity control company. The important role of the climate control company included bringing in desiccant dehumidification equipment, designing the distribution method and assuring the critical SSPC (Society for Protective Coatings) surface preparation standards were met to eliminate any delays due to introduced moisture or weather.
• Sand blasting versus water jetting
A unique component of the Neptune Bulk Terminals project was the contractor’s decision to utilize ultra high pressure water jetting (UHPWJ) for the steel surface preparation rather than the sand blast method used on the previous loader conveyors. Dry abrasive blasting has been the workhorse for decades. Ultra high water jetting is not a common surface and preparation tactic, although it is gaining popularity with many large coating contractors.
The contractor realized there were clear advantages to using the water jet blasting versus sand blasting. In sand blasting applications, a blast aggregate is used to blast paint off of the metal. It leaves a dry surface but one has to protect the surface from thermal rusting which is typical of surface preparation applications.
Previously, the contractor elected to blast and coat coal loaders at the location by sand blasting. This method required tens of thousands of pounds of sand blast media that had to be shipped to site by truck, blasted and then removed from the area. It was a whole operation in itself. Additionally, because the previous paint was lead based, it was a hazardous waste that had to be properly handled.
For the potash conveyors, using water jets only required bringing in the jets, managing the water stream that was leaving the enclosure, and making sure the dehumidifiers were running properly. The challenge was drying such a large containment area in such a short amount of time. The use of water jets required special attention to the need to rapidly dry the steel upon completion of the blast work and emphasized the importance of utilizing desiccant dehumidification equipment for drying the containment areas.
• Project bid to surface preparation standards
The project was bid to conform to SSPC – SP 12 “Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating” set forth by the Society for Protective Coatings. This standard describes the use of waterjetting to achieve a defined degree of cleaning of surfaces prior to the application of a protective coating or lining system.
These requirements include the end condition of the surface plus materials and procedures necessary to verify the end condition. This standard is limited in scope to the use of water only.
This standard is written primarily for applications in which the substrate is carbon steel. However, waterjetting can be used on nonferrous substrates such as bronze, aluminum, and other metals such as stainless steel.
The project also specified that dehumidification be in conformance to SSPC-TR3 Standard (dehumidification and temperature control during surface preparation, application, and curing for coatings/linings of steel tanks, vessels and other enclosed spaces) SSPC-TR3 specifies why and how dehumidification and temperature control are being used to achieve higher-quality coating/lining projects. The document discusses methods of dehumidification, sizing equipment, the impact of contaminants and relative humidity, the uses of dehumidification and temperature control equipment, and inspection instrumentation. An appendix provides information about the relative humidities at which different contaminants can bring moisture to the surface.
• Project stages
The entire project required the management of the enclosure, blast work, drying and coating application. In the first step, CCS contracted a scaffolding contractor to build a frame around each conveyor and built a floor suspended below the conveyor for traffic. Then the contractor shrink wrapped the area for full environmental containment of lead paint and waste water run-off control at dockside. Each containment was nominally 175’ long, 40’ high and 30’wide, although it was not a uniform enclosure. Within the scaffolding numerous stairways, landings and decks needed to be constructed to allow access to the complex steel structure.
Ultra high pressure water jetting began after the area was contained. Eight total guns running at 35,000 psi for 20 hours a day released an estimated two gallons of water per minute into the enclosure and blasted off years of hot potash build up and paint from the steel conveyors.
After the water jetting, dehumidification equipment was activated to immediately dry the bare wet steel and hold indoor air conditions for prime and finish coat painting. MCS was allotted 48 hours in the schedule to dry the assembly and ready the area for coating. The fact that 80 percent of the area within the scaffolding area was ready to paint within the first 12 hours is a testament to the advantage of using desiccant dehumidification.
After the initial drying in the containment, the average conditions were maintained at 68-72 deg F and RH around 35%, with the resultant dew point in the low 40 deg F. This allowed the base coating, a surface tolerant hi-build epoxy primer with aluminum pigment, to be applied just a few hours after drying began, and within ideal dry times for the product.
The finish coat, a high build, high solids surface tolerant epoxy maintenance coating, again with an aluminum pigment, was then applied, again in ideal coating conditions.
The coating was applied unimpeded by moisture issues.
A unique component was how the dehumidification distribution was set up within containment. Generally in surface preparation there is only one opening for the dehumidified air to enter, but MCS technicians for this project determined that an internal ducting distribution system would be the most effective. This system ensured that all areas of the containment received dehumidified air.
By water blasting, there were no excess loading on the docks, cleanup or disposal fees. Additionally, Neptune Terminal’s existing run-off containment systems handled the excess water, eliminating any environmental issues.
• Importance of desiccant dehumidification
Though the decision to blast via water jet was the more efficient option, it also made the use of climate control equipment to prepare the area for coating a critical component. Water jetting leaves an extremely wet surface because it uses ultra high pressure and certainly raises the surrounding moisture and humidity levels, especially in confined spaces. It was the task of the climate control company to hold the blast and physically remove the moisture in a very short timeframe so that the bulk water from the blast didn’t create additional rust.
The more efficient, productive, reliable and faster method of moisture removal is aggressive drying through a desiccant dehumidification system. This process consists of drawing ambient air through a desiccant substrate which captures moisture from the air on the flutes within the wheel. This process is called adsorption. The saturated wheel is then dried by a separate heated air stream to reactivate the wheel. The air is delivered to the space at extremely low dew points and relative humidity levels.
Desiccant dehumidifiers have proved effective to create low relative humidity and dew points when drying air at a condition far from saturation or at low temperatures. Portable units, delivered to the site on trailers, are designed to provide the aggressive drying required to establish and maintain proper dew point and humidity levels. Portable, inflatable plastic ducts are used as part of the airflow system and temporary enclosures are erected to contain the dry air.
The size and scope of the Neptune Bulk Terminals project gave Munters the opportunity to utilize a new, technologically-advanced line of desiccant dehumidifiers -- the DHI-125-ESU Integrated Custom Air Handler (ICA) that operates on both natural gas and electric power. MCS operated two units on each conveyor for a total of between 18,000 and 20,000 cfm for each containment area.
The ICA line of full-featured, factory-built custom air handling systems incorporates many advanced features including an innovative double wall construction that incorporates a superior no-through metal design in either 2.5 or 4-inch wall thickness. Unlike other custom air handlers, the ICA maintains its no-through metal design on all surfaces, even the system base.
During the Neptune project, the ICA equipment ran on propane reactivation and electric generator as a cost saving measure as using all electric power generation would have been more expensive. This decision resulted in an overall reduction in fuel costs of about $6,500.00 per containment compared to all electric diesel generator fuel consumption.
Another cost effective feature: the unit utilizes Munters’ PowerPurgeTM technology, an energy recovery option that improves performance by delivering air at drier levels, while using significantly less energy than traditional active desiccant dehumidification systems.
• Energy-efficient unit utilized
Munters PowerPurge system with ICA units improves performance by delivering air at drier levels, while using significantly less energy than traditional active desiccant dehumidification systems.
The energy efficient technology is completely isolated from both the process and reactivation streams, resulting in three times the performance of a standard internal purge. The system acts as an energy recovery system, collecting waste heat off of the hottest section of the desiccant wheel and using it to help with the regeneration. This reduces the energy required for reactivation while lowering the discharge temperature of the process air, decreasing energy costs for post cooling. It’s possible to experience energy savings of $100,000 annually on a 28,000 cfm system with use of such a recovery option.
The energy recovery option also can reduce the initial capital investment. Equipping a desiccant system with an energy recovery system can reduce the size of the desiccant rotor without diminishing the dehumidification capacity while still decreasing energy costs. Because PowerPurge increases moisture removal performance, a system that required, for example, an 86-inch desiccant wheel may only need a 60-inch wheel if equipped with the energy recovery option.
Use of the system does not affect the size of the air handling system because it is contained within the same housing that contains the desiccant wheel. Other external devices, such as energy recovery wheels or heat pipes, are more expensive and less efficient, and require additional space, increasing the size and cost of the air handling system.
A number of moisture load engineering calculations were run prior to the project to ensure the proposed equipment would meet the project’s critical demands. Engineering calculations were calculated for the Munters desiccant equipment based on seasonal normals for the area. Thirty-year normals for Vancouver during the May/June project dates averaged about 58 degrees F / 15 C, and humidity above 80%, or about a 54 degrees F dew point. There was little margin for error as any shift in the temperature would result in condensation on the surfaces.
The desiccant equipment took this ambient air to dew points well below freezing, so the typical paint specification a 5 degree dew point spread was easily met.
As a side note, all the initial engineering was based on a mid summer project schedule. When Neptune Terminals asked for the project to be moved ahead by two months, there was no little concern over the schedule. However, a quick look at the engineering confirmed that the specified equipment would fully meet the task.
• Project completed successfully
The use of desiccant dehumidification equipment is an important component in blasting and coating applications, especially in UHPWJ projects. The use of UHPWJ is growing as many coating professionals believe in waterjetting’s improved surface preparation results in better and longer coating adhesion, and is a more environmentally sensitive and user friendly method of surface preparation.
Due in a large part to the use of innovative desiccant dehumidification, the Neptune Bulk Terminals project did not experience delays from weather or surface preparation. The coatings, while designed to handle UHPWJ projects, experienced no moisture issues as all finish coats were applied in a fully controlled atmosphere. In addition, the anticipated life span of coating met the owners’ expectations, and the ship loaders were back in operation ahead of schedule.
Questions about this case study? Contact the author at:
Gregg Lowes / E-mail: firstname.lastname@example.org / on the web: www.munters.com / telephone: 1-800-MUNTERS