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Flowserve launches high-reliability seal for light hydrocarbon service pumps

21 April 2006

Flowserve has introduced the QBQ LZ contacting-face mechanical seal, featuring Precision Face Topography and a patented wavy face seal design. The QBQ LZ provides high-reliability sealing with low emissions, and sets a new standard as the high-reliability sealing solution for pumps in light hydrocarbon service at low vapour pressure margins.

Optimized for service with light hydrocarbons of specific gravity between 0.40 and 0.60, the QBQ LZ is designed for use in refineries and the general hydrocarbon processing industry pumping ethane, ethylene, propane, propylene, butane and other related liquids. Light hydrocarbons present unique challenges for these facilities because of their natural tendency to flash from liquid to vapor at ambient pressure and temperature conditions. Vaporisation leads to dry-running of seal faces and premature seal failure, which results in the double failure of not meeting emissions and reliability objectives.

“Equipment reliability is a key plant metric today,” says Mark Fallek, vice president of marketing, Flowserve Flow Solutions. “Refineries are constantly looking to improve their best-practice mean time between repair (MTBR) and maximize plant productivity.”

“At the same time, environmental legislation around the world is increasingly taking aim at reducing hydrocarbon and volatile process emissions to the atmosphere,” adds Fallek. “Refineries seeking to increase their reliability, MTBR and emissions control have a new weapon in the QBQ LZ.”

The QBQ LZ, a new model of the industry-standard Flowserve QBQ seal, addresses the problem of vaporisation in light hydrocarbon service at low vapour pressure margins by altering temperature and pressure dynamics on the seal faces. Using Precision Face Topography technology, smooth, low-amplitude patented wave patterns are laser-machined onto the seal face to create a stable hydrodynamic effect that changes the pressure profile on the seal faces and reduces friction and contact loads without increasing leakage.

The patented wavy face design of the QBQ LZ produced by Flowserve laser machining process features precise, repeatable patterns and smooth surfaces across the seal faces. Smooth surfaces are critical to the success of the QBQ LZ contacting-face design, as they prevent the entrapment of solids and enable the QBQ LZ to achieve its dynamic effects.

These dynamics occur as fluid pressurises on the wave peaks of the QBQ LZ at pressures several times higher than seal chamber pressures, driving vapour back into liquid. Vaporisation is pushed as close as possible to the inner diameter (ID) of the seal, leaving the QBQ LZ seal faces primarily wet with stable flashing and little seal-generated heat. This prevents dry-running, enables the QBQ LZ to operate at extremely low vapour margins, and promotes long and reliable operation.

QBQ LZ technology satisfies all API 682/ISO 21049 design and qualification test requirements for single- and dual-arrangement seals. Because it is based on the standard and widely used Flowserve QBQ seal, the QBZ LZ is easily retrofitted by simply changing the rotating and stationary seal faces with minimal inventory impact and quick implementation times. The QBQ LZ offers the same basic construction as the QBQ, including a rugged cartridge design and multi-port flush injection.

Beyond its application for vapour pressure margins between 5.0 and 50 psi, the QBQ LZ can also be used for high-pressure pumps above 20.7 bar at any vapour margin. The QBQ LZ operating range includes pressures from 0 to 51.7 bar, temperatures between -40 to 203 degrees C, speeds between 6.1 to 23 m/s, and sizes between 44.4 to 130 mm.

On double-ended, double-suction pumps, where premature vaporisation is a common concern, the bi-directional QBQ LZ can be installed on either end without pump modifications or other measures normally required to boost vapour pressure margin. “Bad actor” pumps that consistently cause equipment downtime due to vaporisation can realize a dramatic improvement in MTBR after upgrading to the QBQ LZ.

The Flowserve QBQ LZ seal will be on display at ACEHMA 2006 Hall 8 Stand H2 - J9.

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