SUBJECT : 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

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