Austenitic chromium-nickel Stainless Steel 309 Pipes are renowned for its great strength and corrosion resistance. The machining characteristics of Type 309 are identical to those of Type 304, and it is simple to roll shape, stamp, and draw.
The austenitic stainless steel alloy 309 (UNS S30900) was created for use in high temperature corrosion resistant applications. The alloy can withstand non-cyclic oxidation up to 1900°F (1038°C). At about 1850°F (1010°C), frequent heat cycling reduces oxidation resistance.
Alloy 309 can be used at temperatures up to 1832°F (1000°C) in sulfur-containing atmospheres because of its high chromium and low nickel content. Due to its modest resistance to carbon absorption, the alloy is not advised for usage in severely carburizing environments. Alloy 309 can be used in applications that involve mild oxidation, nitriding, cementing, and thermal cycling, however the maximum service temperature must be lowered.
The alloy can precipitate sigma phase when heated between 650 and 950 degrees Fahrenheit (1202 to 1742 degrees Celsius). An amount of hardness can be restored by solution annealing the material at 2012–2102°F (1100–1150°C).
The alloy’s low carbon version is 309S (UNS S30908). It is used because it is simple to manufacture. A high carbon modification called 309H (UNS S30909) was created for improved creep resistance. Most of the time, the plate’s carbon content and grain size can satisfy both the 309S and 309H standards.
Corrosion Protection
Flood Corrosion
The use of Alloy 309 in damp, corrosive conditions is not intended. The high carbon content, which is there to improve creep qualities, has a negative impact on the ability to withstand aqueous corrosion. After being exposed to high temperatures for a long time, the alloy is vulnerable to intergranular corrosion. However, Alloy 309 is more corrosion resistant than most heat resistant alloys due to its high chromium concentration (23 percent).
Corrosion at High Temperatures
In the majority of in-service circumstances, alloy 309 resists high temperature corrosion.
The following operating temperatures apply:
Oxidizing circumstances (2 g/m3 maximum sulphur content)
continuous service at 1922 °F (1050 °C)
2012°F (1100°C) as its highest point
Oxidizing circumstances (maximum sulphur content of 2 g/m3)
Maximum temperature: 1742°F (950°C)
Low levels of oxygen (maximum sulphur content: 2 g/m3)
Maximum temperature: 1832°F (1000°C)
atmospheres that nitrate or carburize
maximum 1562 -1742°F (850 – 950°C)
The alloy outperforms the majority of heat-resistant stainless steels in these environments, but it does not perform as well as Alloy 600 (UNS N06600) or Alloy 800 (UNS N08800).
