Seal metal selection

Selecting the correct metal for the mechanical seal components 5-9

Selecting the best metal for the seal components is usually a simple task. If the pumps’ 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, but if the wetted parts 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” and 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 the chemical resistance of any material is affected by temperature, concentration, stress etc., so check with some one knowledgeable before you specify any material:

CHEMICAL
METAL
Arocolor Bronze
Barium Casrbonate Bronze
Benzene Carbon steel or Beronze
Benzene, hot Bronze
Bromine gas Bronze
Calcium carbonate 303/304 stainless steel
Phenol (carbolic acid) 303/304 stainless steel
Butyl phthalaate Bronze
Dichlorodifluoromethane (F-12) 303/304 stainless steel
Diethyl ether 430 stainless
Ethanol Bronze
Ethanolamine 303/304 stainless steel
Fluorine gas, dry 430 stainless steel
Hydrogen chloride gas, wet Carbon steel
Magnesium sulfate 303/304 stainless steel
Monoethanolamine 303/304 stainless steel
Mixed acids Bronze
Nickel chloride 303/304 stainless steel
Nuclear primary water systems 304 stainless
Potassium bicarbonate 303/304 stainless steel
Potassium chlorate 303/304 stainless steel
Potassium hydrate 303/304 stainless steel
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, 430 stainless steel or Alloy 20
Titanium tetrachloride Carbon steel
Uricacid 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.

What is grade 316 stainless steel?

The material we refer to as grade 316 stainless steel is made from the following ingredients:

MATERIAL
PERCENTAGE
Chrome 18-20
Nickel 8-12
Carbon .08
Iron 64-70
Silicone 1
Manganese 2
Sulphur .030
Phosphorous .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 :

COUNTRY
DESIGNATION
Germany 1.4571 or V4A
England EN58J
Sweden 2343
Hungary K035
Czechoslovakia 17246