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
ArocolorBronze
Barium CasrbonateBronze
BenzeneCarbon steel or Beronze
Benzene, hotBronze
Bromine gasBronze
Calcium carbonate303/304 stainless steel
Phenol (carbolic acid)303/304 stainless steel
Butyl phthalaateBronze
Dichlorodifluoromethane (F-12)303/304 stainless steel
Diethyl ether430 stainless
EthanolBronze
Ethanolamine303/304 stainless steel
Fluorine gas, dry430 stainless steel
Hydrogen chloride gas, wetCarbon steel
Magnesium sulfate303/304 stainless steel
Monoethanolamine303/304 stainless steel
Mixed acidsBronze
Nickel chloride303/304 stainless steel
Nuclear primary water systems304 stainless
Potassium bicarbonate303/304 stainless steel
Potassium chlorate303/304 stainless steel
Potassium hydrate303/304 stainless steel
Potassium OxalateBronze
Potassium permanganateBronze
Pyrogallic acidBronze
Sodium benzoateBronze
Sodium bichromateBronze
Sodium bromideBronze
Sodium chlorateBronze
Sodium citrateBronze
Sodium dichromateBronze
Sodium ferricyanideBronze
Sodium fluorideBronze
Sulfuric acidCarbon steel, 430 stainless steel or Alloy 20
Titanium tetrachlorideCarbon steel
UricacidBronze

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
Chrome18-20
Nickel8-12
Carbon.08
Iron64-70
Silicone1
Manganese2
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
Germany1.4571 or V4A
EnglandEN58J
Sweden2343
HungaryK035
Czechoslovakia17246