321 Stainless steel pipe & tube

What is 321 stainless steel?

321 stainless steel is a material with excellent high temperature stress rupture performance and high temperature creep resistance, and its stress and mechanical properties are better than 304 stainless steel. 321 stainless steel is 18/8 austenitic stainless steel (304) stabilized with titanium. This grade will not suffer from intergranular corrosion after heating in the carbide precipitation temperature range of 425-850°C. 321 is used in applications up to about 900°C, combining high strength, resistance to oxidation peeling and phase stability for subsequent aqueous solution corrosion.

What is stainless steel pipe?

Stainless steel pipe (SS pipe) is a long round steel material that is hollow and extends longitudinally. Stainless steel pipe is widely used in petroleum, chemical, medical, food, light industry, equipment and instruments, structural parts, etc. In addition, when the torsional strength and anti-torsion strength are equal, stainless steel is lighter, so it is often used in mechanical equipment parts and engineering structural parts, and is also commonly used as furniture and kitchen utensils, etc. Stainless steel pipes can be divided into seamless stainless steel pipes and welded stainless steel pipes according to the production process.

Our most common stainless steel pipes are generally 304, 316, and 316L stainless steel pipes. Many people don't know much about 321 stainless steel pipes. What are its characteristics? Today, HSCO, which has 10 years of experience in stainless steel pipe manufacturing, will popularize the knowledge of 321 seamless stainless steel pipes.

1. Material
321 stainless steel belongs to Ni-Cr-Mo austenitic stainless steel. Its metal content is very similar to 304 stainless steel, but due to the addition of titanium, it has better resistance to intergranular corrosion and high temperature strength. Due to the addition of titanium, the formation of chromium carbide is effectively controlled. TP321 Stainless steel composition is:

Ni  9 - 12
Cr  17 - 19
C  0.08 max
N  0.10 max
Fe  Balance
Mn  2 max
Si  0.75 max
S  0.03 max
P  0.045 max
Ti  5xC min
    0.60% max

2. Performance
The metal titanium in 321 stainless steel pipe can prevent intergranular corrosion of pipe fittings. It also has high-temperature stress rupture performance and high-temperature creep resistance; that is, it is not easy to oxidize corrosion, wear, or brittleness or rupture caused by changes in material structure under high temperature conditions such as flue gas and water vapor.

It also has good stress mechanical properties, can resist stress caused by stretching, bending and impact, has good plasticity, toughness, rigidity, elasticity and fatigue resistance; can withstand higher stress without requiring large strain. , can resist impact loads without being destroyed, and is not prone to permanent deformation or fracture under static loads.

3. Uses
The application of 321 precision stainless steel pipes is still inseparable from its superior performance, mainly in chemical heating furnaces, boiler pressure vessels, combustion furnaces, diesel engines, drying equipment, etc., which have extremely high requirements for intergranular corrosion. It mainly works in high temperature environments or open air environments.

After intergranular corrosion occurs, the metal surface still maintains a certain metallic luster, and no signs of damage can be seen by the naked eye, but the bonding force between the grains is significantly weakened, the mechanical properties deteriorate, and it cannot withstand impact, so it is a very dangerous corrosion. The above equipment is all high-risk equipment. Once the accessories in the equipment cannot resist this corrosion, accidents are prone to occur.

Will 321 stainless steel rust?

321 austenitic stainless steel has good corrosion resistance in the atmosphere and is widely used in petrochemical, electric power, bridges, automobiles and other industries. However, the "rust-free" of stainless steel is not absolute. Due to the special use environment, stainless steel will also corrode. Factors such as medium concentration, pH value, and temperature have a greater impact on the corrosion resistance of stainless steel.

For example, if used for a long time in the sensitization temperature range of 450~850℃, stainless steel will suffer from intergranular corrosion. The mechanism is that C combines with Cr at the grain boundary to form Cr23C6 precipitation, which reduces the Cr content at the grain boundary, which is the so-called "chromium depletion". Cr is one of the main elements to inhibit intergranular corrosion. When the Cr content at the grain boundary is less than 12%, the probability of intergranular corrosion will increase.

Read more: 304 vs 321 Stainless steel or Stainless Steel Seamless Pipe Manufacturing Process