There’s much to appreciate about External Floating Roof (EFR) tanks. They are easy to maintain and can be built bigger and for a lower cost than other tank types. Optimizing their performance, however, depends largely on key design factors. One of those major design elements is having an effective drainage system in place to eliminate the precipitation that can accumulate on the roof. Rainwater and snow accumulation adds weight to the roof, exerting extra pressure on the tank’s pontoons and seals. If not mitigated at a specific rate, the roof can lose buoyancy and sink, catastrophically damaging the tank and leaking your petrochemical product into the environment.
With industrial areas increasingly at risk from severe weather events—hurricanes in particular—having a superior drainage system for your floating roof tanks is more important than ever. This is where many tank operators recommend HMT’s Pivot Master®. Introduced in 1982, the Pivot Master® Floating Roof Drain System has a proven, four-decade history of exceptional performance in thousands of tanks worldwide. To illustrate its benefits, let us first review the two basic system types on the market today.
Flexible Hose Drainage Systems
Many conventional drainage systems are constructed from flexible or semi-rigid hoses. These systems facilitate rapid water flow, take up minimal space in the tank, and tend to cost less than other drainage systems.
Flexible hose systems have several drawbacks, however. For example, they are more susceptible to clogging as sediment gradually settles into lower areas of the hose and any offset joints since they do not maintain positive drainage. Hoses are also harder to clean, which can increase maintenance time and cost. Their flexibility increases their movement inside the tank, occasionally resulting in damage to floor plates and other internal components. Dislodged or poorly placed hoses can become pierced or crushed by roof legs, causing leaks that both contaminate and drain away the tank’s product. Failures have also been known to occur within the joints’ O-rings and seals due to extreme internal pressures.
Some manufacturers have attempted to resolve these issues by creating repeatable lay patterns and tethers to keep hoses in place as they rise and fall. Some also offer metal-clad hoses that are more resistant to pressure and damage.
Depending upon their weight, however, metal-clad hoses can exert too much downward pressure on the roof, negating the benefit they were designed to provide. Additionally, maintaining peak performance of a complex hose system generally requires it to be reassembled after maintenance exactly as the manufacturer originally installed it. With many companies reliant on external contractors for maintenance, this does not always occur.
Rigid Pipe Drainage Systems
In response to these issues, some manufacturers have developed rigid pipe drainage systems. These systems are constructed from straight, metal pipes connected by swivel or swing joints. The pipes—placed at a slope to maintain that positive drainage—are installed in a fixed position, allowing the system to rise and fall without fear of unexpected shifting, kinking, or damage to other internal tank components. Rigid systems are also more resilient against intense pressures, corrosion, and settlement issues.
The problems with rigid pipe systems tend to arise in and around the joints. Some manufacturers fail to take into consideration the amount of pressure a drainage system joint will endure, making ones more suitable for external than internal use. Any offset joints used in these systems can also allow sediment to build up, creating bottlenecks that restrict water flow. As a result, these expensive mechanical joints can break down quickly, causing leaks and requiring repair or replacement.
If not designed optimally, rigid pipe systems can also take up more volume under the floating roof, increasing the heel and reducing the working capacity, creating a dead zone under the roof that will limit a tank’s performance.
Why Smart Operators Choose Pivot Master®
HMT’s Pivot Master® combines the best of each drainage type into one system that outperforms them both. The Pivot Master® is a rigid pipe system connected by uniquely designed flexible hose joints. Steel pipes, installed at a continuous slope to ensure positive drainage, prevent sediment from building up in the system. The flexible hose joints allow the system to maintain flexibility without kinking, clogging, or leaking.
Flexible joints in the Pivot Master® system.
The Flexible Joint is the crowning achievement of the Pivot Master® system. It consists of a composite-type hose containing ANSI 150# raised-face flanges secured in place by a pivotal steel side-plate structure. This hose is constructed with internal and external stainless-steel helixes that maintain rigidity under pressure while still allowing the joint to flex as the system rises and lowers with the roof. Layers of both polar and nonpolar elastomeric materials prevent permeation through the hose and provide a 100% aromatic resistant barrier. The reinforced steel side plates keep the hose from binding while ensuring the joint remains flexible enough for worry-free operation. These joints easily withstand all refined petrochemical products, including harsh solvents like Toluene, Benzene and Xylene.
Many Pivot Master® systems have been in continuous, maintenance-free operation for 15 to 20 years. Best of all, they require minimal operating area inside the tank and even come in two low-profile options for low-heel tanks.
Even in a fixed position, the Pivot Master® requires minimal operating space.
Other benefits include:
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No offsets to cause unbalanced loading
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No stresses on roof nozzle, sump nozzle, or hose end connections
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No leaking due to offset joints or deteriorated O-rings, bearings, or seals
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No scraping or dragging on tank bottom
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No lubrication required
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High operating pressure
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Design options for low profile and in-line drainage to maximize operations
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Extended service life
Pivot Master® Floating Roof Drain System can be paired with the Pivot Master® Floating Suction and Skimmer System for additionalperformance.
Like the Floating Roof Drain System, the Pivot Master® Floating Suction and Skimmer System uses flexible hose joints.
Floating Roof Drainage with HMT
Of course, the best drainage system is one that accommodates your particular tank, product, and local climate. HMT’s storage tank experts can help you design a Pivot Master® solution that seamlessly adapts to your tank’s operating size, pressure, temperature, and anticipated rainwater accumulation. Contact us receive a custom quote.
