Alloy 28 is a high-alloy multi-purpose austenitic stainless steel for service in highly corrosive conditions. The grade is characterized by:
| C | Si | Mn | P | S | Cr | Ni | Mo | Cu | N |
|---|---|---|---|---|---|---|---|---|---|
| ≤0.020 | ≤0.7 | ≤2.0 | ≤0.020 | ≤0.010 | 27 | 31 | 3.5 | 1.0 | ≤0.1 |
Due to its outstanding corrosion properties, Sanicro® 28 can be used in the most diverse environments. Listed below are a few examples of applications for which this alloy is particularly suitable.
Today, Alloy 28 or Sanicro 28 is the most widely used metallic material for evaporator tubes in the manufacture of phosphoric acid by the “wet ” method. Several units have now been in service for more than 10 years. The graphite heat exchangers, replaced by Sanicro 28, often had repeated problems with broken tubes and loss of production.
Alloy 28 or Sanicro 28 is a suitable material for piping and heat exchangers, particularly at concentrations of between 40 and 70% of deaerated acid and over 85%. Alloy 28 or Sanicro 28 has approximately the same resistance as Alloy C in concentrated acid (98% H2SO4).
Alloy 28 or Sanicro 28 is used for production tubing, casing and liners in deep, sour gas wells. The material is also recommended for oil wells with a corrosive environment. For these purposes, tubes are supplied cold rolled with high strength. In the solution annealed condition, Alloy 28 or Sanicro 28 is also used as piping for transporting of corrosive oil and gas and for heat exchangers in treatment facilities. Sanicro 28 wirelines are used for lowering tools and controlling instruments in deep oil and gas wells.
Fluoride-bearing off-gases can form during the manufacture of phosphoric acid and mixed fertilizers. These off-gases must be disposed of for environmental reasons. Sanicro 28 is ideal for this purpose. Tests have shown it to be preferable to higher alloyed CrNiMo grades for the recovery of fluoride-bearing gypsum.
Due to its high resistance to SCC, pitting and crevice corrosion, Sanicro 28 has been selected for heat exchangers in nuclear power plants.
Its high resistance to pitting and crevice corrosion makes Sanicro 28 a very suitable material for seawater-carrying piping and seawater-cooled heat exchangers. This is confirmed by practical experience.
Sanicro 28 has replaced nickel alloys, CuNi, bimetallic tubes and coated carbon steel tubes, which failed due to corrosion. The performance of Sanicro 28 has been excellent.
In seawater-cooled heat exchangers and heat exchangers that work with chloride-bearing cooling water, Sanicro 28 offers high corrosion resistance to both the water and the cooled medium.
When a seawater-cooled plant is shut down, there is no need to drain the piping system or flush with fresh water, provided that the shutdown period is shorter than one month and the water temperature is lower than 30°C (85°F).
The duplex stainless steel 2507 is more resistant than Sanicro 28 in sea water.