Hand lay-up, conventional filament winding or a proprietary fabrication method called ORTHOWINDING
Orthowinding is done a a numerically controlled winder, or a two axis computer controlled winder. The hoop winding is approximately 89 degrees. at the same time, axial reinforcement is applied using unidirectional glass.

Advantages of this method are as follows:
OPTIMUM STRENGTH:
The glass reinforcement is a precise alignment with the two axis of principal stress in a vessel. Orthowinding also permits tailoring the proportions of hoop and axial glass to improve hoop and axial strength outside the range that is achievable with conventional filament winding. A typical laminate used in TROY tanks has 71% of the glass in the hoop direction and 29% in the axial, although this proportion varies throughout the tank and with every tank.
BETTER CORROSION RESISTANCE:
Compared with conventional filament winding. This is because: A typical Ortho Wound laminate has higher resin content. Ortho Wound fibers lie adjacent to each other rather than crossing over. Axial glass strands are interrupted, preventing continuous wicking. Ortho winding results in a compact, dense laminate; virtually air free. Precise positioning of glass: Allowing wall thickness to be tapered in steps of 1/64 of an inch or less. There is no part of the structure where the winding angle deviates from the designed angle, as occurs at the ends of conventional filament wound pattern. Ortho Winding is a highly efficient process for creating tank structures. Costs of Ortho Wound tanks are slightly higher than similar filament wound structures, owing to the higher resin content. In most cases, this higher cost is offset by longer vessel life and greater reliability. Troy has been utilizing this process since 1988, with excellent results.

Advantages of Fiberglass

Maintenance in a Pulp and paper mill is an endless battle with extremely reactive chemicals. Different stages of the papermaking process require caustic liquids that seep through invisible cracks in vessel liners and pipelines eating their way through equipment and substantial repair budgets. In addition, older mills suffer the ravages of time. They require significant modifications to meet new environmental standards and the needs of more efficient processes.

Glass fiber reinforced plastic (FRP) has proven to be a long -term solution for many such problems. The two following case histories illustrate how effective and efficient FRP can be in helping older mills meet modern standards, and in containing corrosive chemicals.

With the old blow pit stack literally falling down around their ears, the people at Maclaren Industries knew it was time for a replacement. James Maclaren lndustries Inc. is a division of The Noranda group, and operates a newsprint mill at Masson. Que., 20 miles down river from Ottawa. The stack has been in use since 1930 when the mill was built. "It would have lasted another 50 years if it weren't for the changes in our process that resulted in dryer blow pit gases," said Rodolphe St- Pierre, who managed the FRP project. The wood had shrunk "like a boat out out of water".

Staves were falling out of the upper portion reducing the stack height and creating a safety hazard. A railing and warning signs around the base warned employees of the danger, but a new stack was inevitable.

The replacement had to withstand the mechanical shocks of blow pit gases, and the thermal shocks of temperatures up to 160 degrees F when winter temperatures drop below 0 degrees F. Blows occur six or seven times a day and each lasts about 20 minutes. St Pierre said he considered a stainless steel replacement and another wooden stack but decided on FRP because, among other reasons it has a significantly lower installation cost compared to the alternatives.

" I had heard good things about FRP stacks from other mills In the Maritimes and northern Ontario,'' he added. Vinyl ester resins offer exceptional flexibility and corrosion resistance, and in a blow Pit stack, their high gloss would eliminate the build-up of wood chips saturated with corrosive acids.

The final decision was a stack built by Troy Manufacturing . The company specializes in FRP equipment for pulp and paper, chemical and other industries where corrosion resistance are necessary ; In stacks, piping, ducting, tanks, scrubbers, hoods and fans, etc.

The stack was to be built of DERAKANE 510 A 40 vinyl ester resin from DOW Chemical Canada. Its properties make it ideal: corrosion resistance ; exceptional flexibility rating of 5% elongation; and, with 3% SB203, DERAKANE 510 A 40 has Class I fire resistance as per the ASTM E 84 tunnel test.

Maclaren Industries needed an over all stack height of 87 ft with an interior diameter of 8 ft 5 in. It was built in three sections using the filament winding method, with a 1/8 in. c-type veil and two mats laid upon the mandrel, then 1/4 in. of filament winding.

On site, CCL construction, Cap de la Madeleine, Que., dismantled the wooden stack, assembled the new one on the ground using two butt and strap joints and lifted it into place. The structure weighed just 9000 lb, and using a single crane with a 210-ft arm it was lifted from the mill yard to the top of the blow pit building in less than a hour. When it was almost in place, the fire resistant property of DERAKANE proved beneficial.

Because of a discrepancy between the original plant drawings and the actual construction of the wood stack, a Section of the old steel ring support bracket had to be cut away before the new stack could fit. The cutting torch bathed the stack with sparks of molten steel, but where some FRP resins could have caught fire the DERAKANE got away with only a scorch mark. A little top coat and the mark was invisible.

The FRP blow pit stack has been in operation since March, 1986, and a recent inspection shows it is still performing very well. On August 3 1988 St Pierre climbed into the stack during the mills first scheduled shut down in 3O years. From the bottom of the stack up as high as they could see the FRP surface was as good as new. The laminate was sound with no crazing or cracking whatsoever What's more, there were very few wood chips adhering to the glossy surface , and they washed off readily. Most important, there was no reduction of the stacks interior diameter.

Exceeding Expectations in Pulp and Paper Mill

Being a "first" can have its benefits. Quebec-based Stone Container, Inc., a producer of kraft photographic pulp, has experienced this scenario first hand. In 1993, the mill became the first to use DERAKANE 510N resin in a new, cost effective chlorine dioxide bleaching application.

Construction of the application was prompted by national and provincial regulations requiring reductions in dioxin and furan emissions. To comply with the new mandates, which became effective in 1992, the mill needed to reduce the amount of chlorine in its paper bleaching process.

To reduce emissions, Stone Container implemented a two-stage bleaching process and decreased the chlorine level used in the process from 92 to 50 percent. The mill simultaneously increased the chlorine dioxide level from eight percent to 50 percent, creating a highly corrosive pulp bleaching environment.

These changes required an equipment modification, and the mill considered building a second tile-lined steel tower to accommodate the new two-stage process. However, limited mill space as well as material and installation costs prompted the mill to reject this option.

Instead, Stone Container opted for a new application: a retention tube that would hold the brown pulp stock between the two bleaching stages. In this application, the brown kraft pulp is pumped from the digester to a tile-lined steel pre-bleaching tower. The stock is then pumped to the retention tube where it is mixed with a bleaching solution containing 10 g/l of chlorine dioxide.

The new upflow retention tube enabled Stone Container to add chlorine dioxide gradually to the stock and give it adequate time to be thoroughly bleached. Most importantly, the new application allowed the mill to decrease the level of chlorine in its pulp bleaching, significantly reducing dioxin and furan emissions in the process.

FRP vs. Steel

At the recommendation of its fabricator, Troy Manufacturing in Brockville, Ontario, Stone Container specified FRP for the tube. Several steels were considered, but discounted because of their higher cost, which would have been about double that of FRP "An exotic metal would have been prohibitively expensive - and quite heavy," explained Eric Brouillard, mechanical supervisor at Stone Container. "Since the retention tube was to be installed 9 meters off the ground, we needed a tube that was both structurally sound and lighter to allow for easier installation."

The DERAKANE Resin Solution

To accommodate the increased level of chlorine dioxide, the mill also needed a resin with high corrosion resistance. Troy recommended DERAKANE 510N resin for this application. 'The installation required a resin that could withstand a very corrosive environment as well as an operating temperature of 150 F (66 C) and a design temperature of 167 F (75 C)," said Rafic Moubarac, vice president of sales and marketing at Troy. "Since DERAKANE 510N resin had performed well in other applications and we had received a recommendation from Dow, we felt that the resin would meet the stringent conditions of the new bleaching process."

Layered Construction

For the tube's corrosion barrier, the fabricator used a hand lay-up technique. For the structural portion of the tube, Troy Manufacturing used its own orthowinding fabrication method with an MEKP cure, adding 3 3/4 percent Nyacol APE-1540 to make the tube more flame retardant. At Dow's recommendation, the structure was post-cured - another technique that has added to the application's longevity and corrosion resistance. The laminate was fabricated with DERAKANE 510N resin.

Exceeding Expectations

The performance of the resin exceeded both the mill's and the fabricator's expectations. Recently, Moubarac and Dow technical service representatives visited Stone Container to check the retention tube - four-and-a-half years after installation. "We visually inspected the tube and were able to show the customer that the veils were like new," said Moubarac. "We also tested the hardness of the manway cover's interior surface, which, because it is exposed to the same chemicals, would also reflect the condition of the veils. We could not penetrate the cover's inside surface with a screwdriver."

The success of this application may be of particular interest to U.S. pulp and paper manufacturers. In the coming years, the U.S. pulp and paper industry must comply with the new EPA cluster rules by eliminating chlorine and switching to other paper bleaching systems such as chlorine dioxide. Like Stone Container, American mills will confront processing challenges as they amend their equipment to accommodate greater chlorine dioxide levels.

Pulp and Paper Case History

Market: Pulp & Paper
Customer: Stone Container Inc., Portage DuFort, Quebec
Equipment FRP upflow retention tube measuring 12 meters x 1 meter.
Operating The tube must withstand the conditions: corrosive nature of chlorine dioxide as well as operating temperatures of 150 F (66 C) and design temperatures of 167 F (75 C).
Fabrication: Hand lay-up and Orthowinding
Resin Used: DERAKANE 510N resin
Fabricator: Troy Manufacturing, Brockville, Ontario
Service Four-and-half years after
Years: installation, the application continues to exceed expectations.
Source: DERAKANE NEWS, Vol. 17, Issue 1, March 1998