Choosing the metal parts for the seal

CHOOSING THE METAL PARTS FOR THE SEAL SA002

Selecting the best metal for the seal components is usually a simple task.

If the pump’s wetted (they get wet from the pumpage) parts are manufactured from a non-metallic material such as Teflon®, Kynar, Polyethylene, etc. we choose non-metallic seal components.

The above illustrations describe two seal designs that operate with no metal parts exposed to the sealing fluid. Please note that in both cases the seals are clamped to the shaft. You cannot use sets-crews in these designs because non-metallic seals are often used on glass coated shafts.

  • If the wetted parts of the seal are manufactured from iron, steel, stainless steel or bronze, and they are not showing signs of corrosion, the seal components (with the exception of the springs) can usually be manufactured from grade 316 Stainless Steel.
  • The springs must be manufactured from “Hastelloy C” or a similar corrosion resistant material to avoid the problems associated with Chloride Stress Corrosion of the 300 series of stainless steel.

There are exceptions to all general rules however, and it turns out that there are a number of places we cannot use grade 316 stainless steel seal components successfully and yet iron, steel, other grades of stainless steel or bronze are usually satisfactory.

The following list describes some of those chemicals and identifies the metal normally selected by the equipment manufacturer for chemical resistance. Keep in mind that temperature, concentration, stress etc. affect the chemical resistance of any material, so check with someone knowledgeable before you specify any metal components.

CHEMICAL
METAL
Aroclor Bronze Bronze
Barium Carbonate Bronze
Benzene Carbon Steel or Bronze
Benzene, Hot Bronze
Bromine Gas Bronze
Calcium Carbonate 303/304 Stainless
Phenol (Carbolic Acid) 303/304 Stainless
Butyl Phthalate Bronze
Dichlorodifluoromethane (F12) 303/304 Stainless
Diethyl Ether 430 Stainless
Ethanol Bronze
Ethanolamine 303/304 Stainless
Fluorine Gas, Dry 430 Stainless
Hydrogen Chloride Gas, Wet Carbon Steel
Magnesium Sulfate 303/304 Stainless
Monoethanolamine 303/304/430 Stainless
Mixed Acids Bronze
Nickel Chloride 303/304 Stainless
Nuclear Primary Water Systems 304 Stainless
Potassium Bicarbonate 303/304 Stainless
Potassium Chlorate 303/304 Stainless
Potassium Hydrate 303/304/430 Stainless
Potassium Oxalate Bronze
Potassium Permanganate Bronze
Pyrogallic Acid Bronze
Sodium Benzoate Bronze
Sodium Bichromate Bronze
Sodium Bromide Bronze
Sodium Chlorate Bronze
Sodium Citrate Bronze
Sodium Dichromate Bronze
Sodium Ferricyanide Bronze
Sodium Fluoride Bronze
Sulfuric Acid Carbon Steel or 430 Stainless
Titanium Tetrachloride Carbon steel
Uric Acid Bronze

If you have any doubt about the compatibility of 316 Stainless Steel with your pump, you can check your facility for any experience you might have with 316 stainless parts in a similar service. If no such experience exists and you are uncomfortable making the selection, contact a qualified metallurgist.

As an additional matter of interest the material we refer to as grade 316 stainless steel is made from the following ingredients:

  • Chrome 18-20 %
  • Nickel 8-12 %
  • Carbon 0.08 %
  • Iron 64-70 %
  • Silicone 1%
  • Manganese 2%
  • Sulphur 0.030 %
  • Phosphorous 0.045 %

The designation 316 stainless steel is not used in all countries. The following list shows the designations used by some other nations for a similar product:

  • Germany 1.4571 or V4A
  • England EN58J
  • Sweden 2343
  • Hungary KO35
  • Czechoslovakia 17246

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Posted

  • On February 17, 2018