• Definition of Stainless:
Stainless Steel: A family of alloys that show marked resistance to corrosion and chemical attack. (300 series contain high chrome & nickel).

• Reasons to Use Stainless:
A. Cleanliness is maintained in the product being transported.

B. Prevention of contamination of the product from small particles or rust & scale.

C. Resists corrosive attack from hundreds of industrial and chemical solutions or mixtures.

D. Greater strength at elevated temperatures.
  Example: At 1000 deg. F, strength for weld fittings or pipe is based on:
  A234 Carbon Steel (WPB) has allowable stress = 2,500 PSI
  A403 Stainless (WP304) has allowable stress = 13,750 PSI
  A403 Stainless (WP316) has allowable stress = 15,300 PSI

E. Cryogenic service (superior mechanical properties at sub-zero temperatures.)

F. Retains lustrous appearance Indefinitely

• Definitions, Types of Stainless
There are several kinds of stainless and they are defined below for your information. Generally when people talk about stainless (particularly in the piping Industry) they are talking about AUSTENITIC stainless - the 300 series - which Is the type of stainless stocked and sold by Robert-James Sales.

1. Martensitic: 13% chrome, .08-2% carbon. Can be hardened by heat treatment and is magnetic.
Example: Type 410 - has good ductility & Corrosion resistance. Used for trim on cast steel valves.

2. Ferritic: 17% chrome & same carbon as martensitic. Higher chrome imparts increased resistance at elevated temperatures. Lack of tensile strength and poor machinability restricts its application.

3. Austenitic: (300 Series). Chrome 16-25%, Nickel 8-20,.15% carbon max. can be modified by the addition of molybdenum, titanium or tantalum. It is non-magnetic, has superior corrosion resistance than straight chrome stainless. Mechanical properties can be increased by cold working. Has a wide range of mechanical and physical properties making it highly desirable for piping applications.

4. Avesta 2205 is a Duplex Stainless combination of Ferritic & Austenitic. It has higher corrosion resistance than 316 (3% min. Moly vs 2% in 316), highly resistant to stress corrosion & Chloride cracking. It is cost effective because it has only 5% Nickel. Duplex stainless has high strength, ductility, toughness and weldability.

5. AL-6XN ® is a superaustenitic stainless steel which was developed by Allegheny Ludlum Corporation. It exhibits far greater resistance to chloride pitting, crevice corrosion and stress-corrosion cracking than exhibited by the standard 300 series stainless steels, and is less costly than the traditional nickel-base corrosion resistant alloys.
The AL-6XN alloy has exhibited good performance in variety of highly corrosive environments. The AL-6XN alloy is available in a wide range of product forms including plate, strip, sheet, bar, billet, tubing, pipe, and castings. Its various product forms are covered by ASME and ASTM specifications. The use of wrought AL-6XN products in the ASME Boiler and Pressure Vessel is covered by Code Case 1997 (latest revision) for Section VIII construction and by Code Case N-438 (latest revision) for Section III construction. The use of AL-6XN castings is covered by Code Case 2106 (latest revision) for Section VIII and Code Case 497 (latest revision) for Section III construction. The alloy is approved for both welded and unwelded construction under ANSI/ASME B31.1 Code Case 155. Use of AL-6XN alloy in contact with hydrogen sulfide-containing petroleum and natural gas is covered by NACE MR0175-92.

6. 254SMO is an austenitic stainless steel designed for maximum resistance to pitting and crevice corrosion. With high levels of chromium, molybdenum, and nitrogen, 254SMO is especially suited for high chloride environments such as brackish water, seawater, pulp mill bleach plants and other high chloride process streams. 254SMO offers chloride resistance superior to that of Alloy 904L, Alloy 20, Alloy 825 and Alloy G. 254SMO is compatible with the common austenitic stainless steels. It is often used as a replacement in critical components of larger constructions where Type 316L or 317L has failed by pitting, crevice attack, or chloride stress corrosion cracking. In new construction, 254SMO has been found in many cases to be a technically adequate and much less costly substitute for nickel-based alloys and titanium. 254SMO is substantially stronger than the common austenitic grades, but is also characterized by high ductility and impact strength. 254SMO is readily fabricated and welded.