Fabricated Plastics Limited

Material Matters - An Engineering and Fabrication Challenge


Courtesy of Fabricated Plastics Limited

The world of engineering is a very large and diverse universe which ranges from electrial, mechanical and civil to environmentaland structural. It is true that their varied disciplines have many qualities in common, e.g. the mixture of logic, creativity, awareness of cost /benefit ratio etc., are requirements of all engineering. It is equally true that each discipline has its own mind set, culture and 'best practices.' One of the key differences between engineering disciplines is the materials they work with.

Steel, concrete, wood and plastic obviously behave differently from each other and the differences in stress levels, expansion rates and various tolerances are enormous.

A recent project successfully completed by Fabricated Plastics of Maple, Ontario, just north of Toronto, demonstrates some of these differences in engineering cultures. It also testifies to the ability of good engineering firms to change hats, modify their usual practices to accomplish a goal.

The project involved a huge Petrochemical plant in the U.S. Within the plant there was a process which emitted a large volume of sulphuric acid. The requirement was to capture this acid and other pollutants, and convert it into sodium bisulphate - a useful commodity to the water treatment and fertilizer industries. The Petrochemical plant contracted with a process engineering company who specializes in the environmental controls for pollution abatement equipment, at power plants and petrochemical refineries. Typically, the equipment would include storage tanks, pollution control equipment such as scrubbers and other filtration devices. The process is largely the same in most applications but it varies in size and capacity.

The process engienering company, contracted with a specialized consulting engineering company that had wide experience in the petrochemical industry, who in turn worked with Fabricated Plastics and thus began the story of co-operation between two different engineering approaches.

The petrochemical industry requirements for engineering demand extremely high standards and tolerances since they are dealing with highly volatile substances. Historically, the vast majority of their equipment is fabricated from steel and other metals.

Using Fibre Reinforced Plastic (FRP) equipment is very rare in the petrochemical industry. Rare to the extent that the engineers from the other companies Fabricated Plastics dealt with, knew very little about the material and had no previous experience with its use.

Meetings, phone calls and e-mails ensued during which the two disciplines combined and formulated a plan which covered every conceivable difference in behavious of the two materials. That alone is an outstanding achievement.

Of course, having a plan in no way means that all the problems are solved. Rather it is a strategic plan that shows the order in which things should be done, how everything will work through the design process, and acts as a guideline for the whole procedure. In fact, the list of problems and challenges was quite lengthy.

The equipment had to be designed to fit into a limited and defined space.

Wind load and seismic considerations.

The equipment had varying chemical, temperature and pressure conditions and some chemical erosion concerns.

The equipment would need to be installed without grout on vessel bottom pads.

The equipment would require hydrostatic testing at Fabricated Plastics prior to shipping to the installation site

The FRP Equipment Consisted of 8 Items:

  1. TK-721 /722 & 733: 3 Sodium Bisulphite Storage Tanks
    1. 4.0 m (13'-1 1/2' diameter x 35 ft high, flat bottom, dished top)
    2. Design pressure /temperature: + or - 20' at max. 210 degress F
    3. Weights: 13,000 lbs empty: 420,000 lbs operating
    4. Hydrostatic test in vertical position, flooded + 6 psig at top
    5. The Client had asked for groutless installation for tanks with flat bottoms, which meant they were required to have flat, smooth and square bottoms. This was especially critical for these 3 relatively tall tanks.
    6. As the tanks had flat bottom which would not withstand the loads of hydrostatic testing, the tanks had to be anchored to a steel base plate, specially designed for the hydrostatic pressure test, to prevent the flat bottom from bulging under hydrostatic load and lifting off the tank test pad.
  2. TK-224: Emergency Water Head Tank
    1. 7'-6' diameter x 10' high integral flat top, dished bottom and split steel support ring
    2. Design pressure /temperature: Atmospheric at max. 210 degrees F
    3. Weights: 3,350 lbs empty: 31,900 lbs operating
    4. 10 ft high test platform had to be built to support the tank from the support ring for the hydrostatic test in its operating position.
  3. TK-731: 30% Sulphuric Acid Surge Accumulator
    1. 10' diameter x 10' high, flat bottom, dished top
    2. Design pressure /temperature: + or - 20' WC at max. 210 degrees F.
    3. Weights: 3,400 lbs empty; 63,000 lbs operating
  4. T-709: Condensate S02 Stripper
    1. Sump tank: 6' diameter x 6' high with conical top and dished bottom with 7'-3' high skirt Stripper Tower: 3'-6' diameter x 23'-6' high with dished top
    2. Overall height = 39'-2'
    3. Design pressure /temperature: +14.9 psig at max. 210 degrees F.
    4. Weights: 3,250 lbs empty; 18,200 lbs operating; 31,000 lbs flooded hydro test
    5. Hydrostatic pressure test in vertical position, flooded +16.5 psig at top
  5. T-704: Quench Separator (Candle Filter)
    1. 12' diameter x 36' High cylindrical shell, c/w dished top and bottom and support skirt
    2. Overall height = 46'-3'
    3. Design pressure /temperature: +14.9 psig at max. 210 degrees F.
    4. Weights: 25,000 lbs empty; 128,500 lbs operation: 301,000 lbs flooded hydro test
    5. Hydrostatic pressure test in vertical position, flooded +16.5 psig at top
    6. 42' diameter gas inlet nozzle c/w removable quench spray spool assembly
    7. Opposite the inlet nozzle, between the corrosion liner and the structural layers, an additional 22 layers of 1.5 oz mat provided for erosion allowance
    8. The base of each of the 16 internal 'candle' filter elements (supplied by others) are bolted to and supported by 18' diameter flanges, connected to a flat 'tube-sheet'. For optimum corrosion resistance and structural integrity, the engineers at FPL decided to have these 16 flanges laminated integrally with the flat tube-sheet, eliminating joints /secondary bonds. Stiffener beams and cross braces underneath the tube-sheet had to be custom designed and fitted into the tight spaces available between the flanges.
    9. The cylindrical upper and lower shell sections, consisting of corrosion liner plus 1/8' HLU structural laminate, were first joined to the central tube-sheet and both dished ends. After adding the proper knuckle reinforcements, the entire cylindrical shell and support skirt were then monolithically reinforced with a combination of helical winding and uni-axial layers, to satisfy the combined bi-axial load due to internal pressure plus axial loads due to the internal candle filters plus wind /seismic loads.
  6. T-707: S02 Scrubbing Tower
    1. 8'-6' diameter x 92'-5' high c/w conical top and dished bottom + support skirt
    2. 3' diameter x 26'-10' high stack on top of the tower
    3. Total height = 119'-3' including stack
    4. Design pressure /temperature: +14.9 psig at max. 210 degress F.
    5. Weights: 20,000 lbs empty; 108,000 lbs operating
    6. 3 x 10' packed beds; 3 x liquid distributors: 2 collector tray sections
    7. Hydrostatic pressure test at 25.5 psig, in horizontal position using suitably spaced support saddles
    8. During the design of the 120 ft tall tower and stack, coordination between the consulting engineering company and FPL engineers enabled the use of lateral supports at four levels from the open building steel structure. These lateral supports were necessary to brace the tower against wind and seismic loads, thus reducing the bending moments and anchor bolt requirements at the base.
    9. The sheer length of the tower, combined with the requirement for no field joints (flanged or otherwise) plus integrally moulded packing support ledges, required special tooling, careful production planning and coordination with other ongoing projects on the shop floor
    10. The remaining support ledges, which had much lower loads, were laminated into pre-moulded 'undercuts' in the shell to achieve mechanical anchoring, in addition to the chemical adhesion provided by the standard secondary bonding operation
    11. Internal wide flange support beams were custom designed and custom made of hand lay-up construction, and had a corrosion liner with mould surfaces all around
  7. E-705: Gas Condenser Inlet and Outlet Heads
    1. 5' dia. x 8' long, FRP heads for a metal Gas Condenser by others
    2. Each head had an integral dished head on one end and 5' diameter flange on the other end. The flange had steel back up rings to match to Condenser flanges
    3. Derakane 441-400 resin throughout with fire retardant 510C-350 on the outer layer.
    4. Design pressure /temperature: +14.9 psig at max. 210 degrees F.
    5. Empty weights: 1,600 lbs & 2,000 lbs
  8. D706: Gas Cooler Separator
    1. 6' diameter x 6'-8' long FRP housing for horizontal flow Gas Separator
    2. With 72' x 36' concentric reducers at each end with 36' flanges
    3. Derakane 441-440 resin throughout with fire retardant 510 -350 degree C. on outer layer
    4. Design pressure /temperature: +14.9 psig at max. 150 degrees F.
    5. Empty weight: 1,500 lbs

In addition to the list of general problems and challenges, other situations presented great difficulties.

The large scrubbing tower (92.5') was to be installed into and supported by a steel structure on site. No such structure existed at Fabricated Plastics testing area, the tower had therefore to be tested horizontally.

This is most unusual as the tower was not designed to be horizontal, and not designed to be totally full of liquid. Fabricated Plastics managed by laying the tower on its side, fully flooded at 25 psi.

Since the tower was designed as an integral unit of 92.5', it had to be shipped in one piece. It took a tractor with 3 trailers to achieve this - a nightmare for even the most experienced heavy equipment truckers. The additional 27' stack presented no problem of course.

The project was completed on time, on budget and when installed it worked without a hitch.

The engineers involved, both at Fabricated Plastics and the consulting engineers all heaved a sigh of relief that it was over and everything worked as planned. Another extremely difficult project completed demonstrating innovative engineering, ingenious thinking, and large production throughput with high quality fabrication.

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