|
FIGURE 1: SUITABILITY OF MATERIALS IN SULFURIC
ACID (MATERIALS IN EACH REGION EXHIBIT A CORROSION RATE OF
5 MPY OR LESS)
In the extreme conditions, the primary
alternative to zirconium is tantalum, and zirconium is significantly
less expensive than tantalum. There are two regions that zirconium
and tantalum are the primary options: 1. Temperatures above
the boiling point and concentrations up to 50% 2. Temperatures
below boiling and concentration from 50 to 70% Figure 2 shows
the iso-corrosion curve for zirconium in sulfuric acid. It
is important to keep corrosion rate of zirconium below 5 mpy.
Reactive metals work because of the passive oxide coating.
When corrosion is above 5 mpy, the coating is being removed
and corrosion rate can increase very quickly with process
upsets. Proper selection of zirconium usually means the application
will not corrode and give useful equipment life of 20 to 30
years. The best results will be obtained if corrosion coupons
are placed in the process or process conditions are duplicated
in a corrosion lab. The Wah Chang corrosion lab is capable
of testing most conditions with sulfuric acid and verifying
what corrosion rates to expect.
Two of Six 1
2 3 4
5 6
|
