PT&P fabricated several big ton spring assemblies consisting of two different models for a refinery expansion project in India. The larger model has an operating load of 25,590 lb. and a design travel of .420″ up.
The smaller model has an operating load of 12,100 lb. and a design travel of .443″ up. The big tons will be utilized to support substantial vertical loads while simultaneously providing a large platform to accommodate axial movement of the piping system across the load flange. Low friction rollers are installed to reduce the sliding friction between the load flange and the bottom section of a pipe shoe.
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PT&P designed and fabricated F-type variables for an oil refinery in California. The variable springs are designed for an operating load of 49,771 lb. and an installed load of 43,000 lb. Two coils are used in tandem to achieve a vertical movement of 1-5/8″ downward. The variables are fabricated from hot-dipped galvanized carbon steel and are customized with an extended load column to reach an installed height of 67-1/2″. The variables for this project are the largest standard double springs offered; however, PT&P can customize to any load specification. Standard load testing was performed prior to shipment.
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This initial order included PT&P’s field services division testing and recalibrating four constant spring supports not manufactured by PT&P. A preliminary inspection of the original constants revealed deformations in the spring coil housing. This is indicative of defective coils; therefore, before any load tests were conducted, inspection windows were cut into the spring coil cover to confirm the initial hypothesis (Figure 2). Inspection of the coils revealed complete deterioration with broken and missing sections of the spring. Subsequent inspections of the remaining three assemblies illustrated similar failures. The original constants were then disassembled (Figure 3) to determine the feasibility of replacing only the coils while utilizing the original frame/cam components.
The original spring coils were different in spring rate, length, and diameter than any standard PT&P coils; therefore, multiple coils were required to duplicate the overall function of the existing coils. Using multiple coils also required modifications to the existing frames. In an effort to expedite the overall delivery schedule, entirely new constant springs were manufactured in one week (Figure 1). The four new constants measure 53″ long, 13″ wide and 86″ tall. They have a 18-3/4″ diameter spring coil with a coil housing of 20-1/2″ diameter. The new constant assemblies are designed for an operating load of 13,332 lb., travel of 13″ upward and 2″ downward for a combined total travel of 15″. A load test throughout the total travel range was performed on each constant.
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The clevis and turnbuckle pictured are each fabricated from individual solid pieces of 304H stainless steel. The 304H material, which has a maximum carbon content of 0.06%, was required because these items are designed to be used in an environment with temperatures up to 1000ºF. The customer’s specifications mandated that no welding would be allowed on either the clevises or turnbuckles. Additionally, no forgings were readily available, so blocks of 304H stainless steel were utilized in this design.
Both the clevises and turnbuckles are made to accommodate rod diameter ranges between 1-1/4″ to 1-3/4″. These components have a maximum load capacity of 18,600 lb. The clevises measure 3″ thick x 5-1/4″ wide x 10-5/8″ tall. The turnbuckles measure 2″ thick x 4″ wide x 9-1/4″ tall. Prior to fabrication, each component was modeled using finite element analysis to determine that stress levels are within the acceptable range.
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