Seal Makers Plug Away

Many new developments focus on niche applications.

By Seán Ottewell, Editor at Large

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The U.S. Environmental Protection Agency's development of enhanced leak detection and repair program directives for valves and valve stem and flange sealing systems is driving this change in emphasis. (See: "Prepare to Clamp Down Tighter on Leaks.") At the moment, existing consent decrees on seal qualification tests are vague, says Drago. Users are directed to employ good engineering practice in their selection of test methods. So, some companies, including Chevron and Shell, have developed their own procedures.

Meanwhile, in Europe, the ESA's best available techniques guidance notes and associated documents (available at www.europeansealing.com) are extremely popular downloads. Ellis believes a major factor for this is the impending European Union Industrial Emissions Directive that draws together separate pieces of emissions legislation.

MORE NEW MATERIALS
A current focus at Greene, Tweed & Co., Kulpsville, Pa., is eliminating catastrophic failures in sealless pumps. Its CeraComp ceramic-matrix composite, introduced in July, targets just that.

The new composite delivers dramatic benefits over traditional silicon carbide materials, having both superior fracture and wear resistance, says the company. This translates into dramatically improved mean time before failures and reduced maintenance costs, it adds.

"CeraComp is capable of withstanding temperatures over 1,100°F (600°C), exceeding the upper limit of polymeric and elastomeric composites, and maintains outstanding chemical resistance, achieving improved durability and longer component life. In addition, CeraComp's excellent toughness enables better structural integrity and impact resistance, eliminating the risk of catastrophic failure for our petrochemical and power customers," notes the firm.

Greene, Tweed currently has developed CeraComp solutions for canned-motor and magnetic-drive pumps. These bearings and bushings suit both rotary and static usage, which dramatically expands their potential, it says.

In May, the company launched two Chemraz compounds for extremely low temperatures. Chemraz 564 LT and 566 LT maintain excellent sealing integrity at high pressures and temperatures as low as -40°F (-40°C) but can handle up to 445°F (230°C), notes the company. The compounds deliver the same chemical resistance as its other leading compounds, plus offer excellent compression set and thermal shock resistance, it adds.

"By developing these new materials, we are successfully filling a gap that will deliver exceptional sealing performance... in colder temperatures than ever thought possible," says Ron Callawa, vice president and general manager of Greene, Tweed's oilfield business.

TURBINE SEAL
Meanwhile, John Crane, Morton Grove, Ill., has introduced a non-contacting seal, the Type 28ST, for steam turbine drivers. It eliminates loss of valuable steam energy via leakage caused by corrosion and shaft damage.

By improving bearing reliability, which normally accounts for 80% of unplanned turbine downtime, these seals reportedly can provide cost savings of $11,000 to $26,000 per driver per year.

Originally designed for centrifugal compressors, the seals' advanced spiral-groove technology was refined specifically for steam turbines. Positioned on the rotating seal face, the spiral grooves pump steam to the root of the groove and toward a non-grooved portion of the seal face, creating a sealing dam that provides resistance to flow and increases pressure.

The pressure generated separates the sealing faces by a precise amount, which adjusts to maintain seal face equilibrium as operating parameters change. The patented non-contacting design reduces steam leakage to less than 5% of that of traditional sealing devices such as segmented carbon rings and labyrinths. The design handles temperatures as high as 752°F (400ºC), speeds as fast as 120m/sec and pressures up to 27.6 bar g.

John Crane also has extended its portfolio with recently added engineered bearings and specialist filtration systems services.

SHAFT SEALING
This year, SKF USA, Lansdale, Pa., debuted a new generation of Speedi-Sleeves for worn or damaged shafts on rotating equipment (Figure 3). These easily installed sleeves provide an excellent sealing surface without requiring shaft disassembly or specifying a new size of replacement seal, says the company. A removable flange simplifies installation without power tools or heating, and shafts can be up-and-running within minutes at a fraction of the cost of traditional reworking, it adds.

The sleeves benefit from a proprietary stainless steel and manufacturing process, which create an optimized seal counterface surface and increased sleeve strength as well as excellent ductile properties. Imperceptible pockets enable lubricant to reside on the sleeve to prevent dry-running of the sealing lip that otherwise could result in excessive wear.


Seán Ottewell is Chemical Processing's  Editor at Large. You can e-mail him at sottewell@putman.net

 

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