321 Stainless Steel Pipes & Tubes

Type 321 is a standard austenitic 18/8 chromium nickel alloy with the addition of Titanium making it an excellent choice in elevated temperature environments. The titanium stabilises the material removing its susceptibility to the effects of intergranular corrosion. 321 is therefore the stainless steel material of choice for applications in working environments up to 900° C. 
A drawback of Type 321 is that the titanium does not transfer well across a high temperature arc, so it is not recommended as a welding consumable. In such instances, 347 is the preferred choice as the Niobium performs the same function as Titanium but can be still transferred across a high temperature arc. Type 347 is therefore the consumable of choice for welding Grade 321. 
The steel has excellent forming and welding qualities and excellent toughness even at cryogenic temperatures. If you are looking for a stainless steel to provide resistance to intergranular corrosion, 304L is the normal choice as it is a more commonly used and supplied steel. 
However, 321 is a much better option in operating temperature environments in excess of 500° C and therefore has its own merits. 
Note that Type 321 does not polish well so it is not practical to use this material as cosmetic architectural feature. 

Product Range

Composition

Typical compositional ranges for grade 304 stainless steels are given in table 1.
Table 1. Composition ranges for 304 grade stainless steel

Mechanical Properties

Typical mechanical properties for grade 304 stainless steels are given in table 2

Table 2. Mechanical properties of 304 grade stainless steel

Physical Properties

Typical physical properties for annealed grade 304 stainless steels are given in table 3.
Table 3. Physical properties of 304 grade stainless steel in the annealed condition

Grade Specification Comparison

Approximate grade comparisons for 304 stainless steels are given in table 4.
Table 4. Grade specifications for 304 grade stainless steel

Corrosion Resistance

Equivalent to Grade 304 in the annealed condition, and superior if a weldment in these grades has not been post-weld annealed or if the application involves service in the 425-900°C range. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 60°C. Considered resistant to potable water with up to about 200mg/L chlorides at ambient temperatures, reducing to about 150mg/L at 60°C.

Heat Treatment
Solution Treatment (Annealing) - heat to 950-1120°C and cool rapidly for maximum corrosion resistance.
Stabilising - heat to 870-900°C for 1 hour per 25mm of thickness and air cool. Stabilisation is recommended for most severe service conditions (above 425°C) and particularly for material annealed at the upper side of the annealing temperature range.
Stress Relief - Heat to 700°C for 1 to 2 hours and air cool.
These grades cannot be hardened by thermal treatment.