Market conditions, environmental regulations and evolving processes cause change, sometimes dramatic change, in a pump’s operating conditions. Some changes in operating conditions can be satisfied with variable speed drivers, but speed is not a magic bullet. Variable pump speed can excite rotordynamic or system stability problems.
Conhagen’s engineers provide cost-effective solutions by designing unique replacement pumps to satisfy changing operating conditions. Conhagen performs rotor dynamics, hydraulic design and welding process development in-house. Two of its seven engineers earned Master of Science in Mechanical Engineering degrees from Texas A&M, one of whom performed bearing tests in the A&M Turbo Lab, and Conhagen’s hydraulics designer has designed and tested hundreds of high-energy centrifugal pumps during his 43 years in the industry. Conhagen backs up its designs with customer-witnessed performance tests.
Conhagen has a library of unique bearing designs for rolling element, hydrodynamic, hydrostatic and hybrid types using conventional oil (splash, ring oil, pressurized or mist) or product lubrication. The company has mastered the art of minimal bearing operating temperatures.
Few of the company’s designs are fully covered by API 610, but Conhagen ensures compliance when possible and identifies all exceptions required to solve unique problems in its proposals.
The company’s engineers work hand in hand with asset owners to identify real problems and their root causes, and then jointly develop solutions that are acceptable to the owners and operators. Conhagen provides customers with all detailed calculations, manufacturing drawings, test reports, and job-specific operation and maintenance manuals.
In 2007, Conhagen replaced a 10-stage axial-split case pump with a six-stage radially-split case pump in diesel fuel desulfurization service at 910 pounds per square inch differential, 200,000 pounds per hour and 450 F. The original pump, a Pacific JTC, became rotor-dynamically unstable every six to eight months, requiring a full refurbishment. Conhagen’s drop-in replacement pump shortened the distance between bearings from 72 to 24 inches, creating a “stiff ” shaft whose first critical (in air) was 4,600 rpm. The replacement pump has only one mechanical seal — a dry gas seal — at the drive end. The journal and thrust bearings are product lubricated hydrostatic types. The only customer connections to the pump are the inlet and outlet nozzles and tubing supplying nitrogen to the mechanical seal. All rotor fits are polygon, requiring no heat for disassembly or assembly.
Shortly after the pump was first installed, a large steam bubble was introduced into the system and crashed the pump. The spare element was installed with Vespel CR-6100 wear parts to survive dry running. Unfortunately, the Vespel CR-6100 thrust disc failed on start-up because o-rings subjected to discharge pressure could not maintain their seal, and the Vespel CR-6100 was blown out of its retainer. Once again, the element was changed out, returning to the original wear part materials. The customer and Conhagen were concerned about another steam event and entrained solids (mostly scale) causing long-term wear. During the next year, Conhagen developed titanium carbide (TiC) coated graphite wear parts. The TiC-coated rings can sustain entrained solids and dry running. However, their low coefficient of thermal expansion complicated integration with the 12-chrome steel components. The spare element was eventually fitted with the magic wear parts and was stored in its container, waiting for an opportunity to change out the element once again.
The TiC-fitted element was installed in 2011, and the pump has now run seven years without any maintenance. It has survived many start-ups and upsets without complaint. An image of the replacement pump is on the cover of Heinz Bloch’s “Pump Wisdom.”
For more information, visit www. conhagen.com or call (409) 938-4226.
