The Spencer Engineering Edge is apparent when it comes to dealing with extraordinary application conditions. Over our corporate lifetime of more than a century, Spencer engineers have faced innumerable challenges and built a database of effective approaches for them.
Special Materials and CoatingsSpencer’s standard material of construction for fabricated, multistage centrifugal blowers and gas boosters is carbon steel with aluminum impellers. Standard coatings are epoxy primer for all interior and exterior surfaces, and a urethane exterior topcoat. Scores of other metals and coatings are available for customized performance.
We have compiled lists of suitable materials of construction for blowers handling gaseous fumes of everything from acetic acid (Type 304 stainless steel) to sodium hydroxide (Hastelloy®), and moist chlorine (Inconel®) to nitric acid (316 SS).
One effective approach is to combine standard and custom materials. Specialized alloys can be used for components exposed to corrosive gases; less expensive materials for unwetted parts. The result is a blower that has special protection where it’s needed and economy everywhere else.
Materials of construction
300 Series stainless steel
400 Series stainless steel
Carpenter 20® stainless steel
Which are better, special metals or coatings?
Coatings are often used for their anti-fouling properties or for passivation of metal surfaces. But in many instances, coatings and special materials are simply two ways of reaching the same result. Selecting one over the other depends on your preferences and circumstances. You need to examine economic factors such as the cost of coatings vs. exotic alloys, and life cycle considerations (e.g., are you looking for 40,000 or 4,000,000 duty cycles?). Spencer has printed evaluative factors to help establish the best choice for specific instances.
Note that coatings can be applied to counter internal or external conditions. A special exterior paint might be used in humid environments to prevent rust, for example. In some cases, special coatings must be accompanied by special materials (e.g., high temperature coatings and high temperature steels must be used together) to deliver consistent results.
Heresite® or Bisonite® baked phenolic
Special paint (e.g., epoxy, enamel, polyurethane)
Maybe a corrosion allowance is sufficient
If corrosion is the problem and its rate is slow, predictable and acceptable, you may be able to avoid using either coatings or special metals. A corrosion allowance involves a blower housing metal that is thicker than usual to accommodate corrosion. Thus, a thick section of 304SS might be used instead of a more costly Hastelloy. The thickness of the corrosion allowance can be planned to reach a desired service life for the blower.
Spencer Shaft Seals
Spencer offers a variety of seals to meet broad application needs. Seal selection is influenced by the leakage rate, seal cost, maintenance requirement and also by the type of process gas, its pressure and temperature. We have published guidelines for seal selection to limit shaft leakage to acceptable levels, balancing seal cost and complexity against sealing effectiveness. Some examples are shown in the accompanying illustrations.
Advantages: Inexpensive, lower leakage than packing box. Low maintenance.
Disadvantages: Limited life capacity, typically two to three years. Leakage increases with time.
Type: Dry, contacting
Cost Factor: $$
Leakage: 0.1–1 SCFM
Max. Temp.: 800°F
Single Mechanical Seal
Advantages: Near-zero leakage, low maintenance.
Disadvantage: Sensitive to misalignment.
Type: Dry, noncontacting
Cost Factor: $$$$
Leakage: 0.01 SCFM
Max. Temp.: 800°F
Double Mechanical Seal
Advantages: Highest sealing effectiveness of all seal types, low maintenance.
Disadvantages: Sensitive to misalignment. Minor contamination of process gas by purge gas.
Type: Dry, noncontacting
Cost Factor: $$$$$
Leakage: 0 SCFM
Max. Temp.: 800°F
NOTE: Cost factors are relative price rankings of seal types shown. Process gas leakage depends on many factors including inlet pressure, differential pressure, shaft diameter, operating speed and seal condition. Leakage ratings are furnished for comparison only.
Gas Sealing Fundamentals
Gas leaks occur most often where the power shaft passes through the blower housing. Every shaft seal leaks, but leakage can be restricted to acceptable levels through proper seal selection.
Dry-running seals are recommended by Spencer because they do not contaminate the process gas with cooling or lubricating liquids. They are also generally simpler, less expensive, easier to maintain, more reliable and longer lasting than wet seals.
Dry-running, contacting seals have touching seal faces that wear, generating a lubricant such as graphite powder. These seals are mainly used for low pressure, low temperature applications. Because they wear continually, these seals generate friction and heat, and must be periodically replaced. The power requirement is higher than for noncontacting seals.
Dry-running, noncontacting seals balance hydrostatic and hydrodynamic forces to keep seal faces from touching during operation. These seals do not wear and hence need no maintenance.
Single and double mechanical seals are preferred by Spencer for handling hazardous, corrosive and poisonous gases. They have very low, unvarying leakage rates. Capability ranges are very broad: temperatures from below 0° to 800°F, pressures from 2 psia to 300 psig, shaft diameters to 4.5″, speeds from 900 to 5000 rpm. Component materials can be chosen for specific chemical resistance, (e.g., titanium mating rings for handling chlorine gas, 316 SS for hydrogen sulfide or 304 SS for wet CO2). O-rings are available in several elastomers for different conditions.
The hermetic gas booster design, while not a sealing concept per se, deserves mention here because it provides wholly gastight performance – the ultimate in leak restriction.
Other areas of customization are in motors, drivers and drive arrangements. We can meet wide-ranging motor specifications such as nuclear qualification, special voltages, explosion-proof designs, etc., or omit electric motors entirely and supply alternative drivers (e.g., steam turbines, diesel engines or landfill gas-fueled engines).
Spencer can supply AC and DC electric motors to comply with the most difficult, wide-ranging specifications including:
50 Hz, 60 Hz and other frequencies
Explosion-proof, chemical-resistant and other special designs
Special lubrication provisions such as low outgassing fluorocarbon-based grease
However, your prime mover doesn’t have to be an electric motor. Spencer can provide steam turbines, gasoline and diesel engines, and other drivers powered by natural gas, propane or landfill gas. You name whatever you need, and we’ll surely know how to deliver it.
Special drive configurations are also easily arranged. You can specify a belt drive for blower operation at a certain speed, or variable frequency drive, or a drive train with a gearbox speed increaser – whatever your application requires.
API blowers and bases
Spencer can supply blowers and bases which comply with specific API standards for petrochemical plants and refineries.