what stainless steel pipe

Stainless steel pipe is a sort of line produced using tempered steel, a metal that doesn’t rust and has something like 10.5% chromium in it. This high chromium content makes an oxide layer on the surface of the steel that protects it from rust and corrosion. This makes it perfect for many uses where durability and corrosion protection are important.

Material composition of stainless steel

Grade 304 Stainless Steel

• Carbon (C): 0.08% max
• Chromium (Cr): 18.0-20.0%
• Nickel (Ni): 8.0-10.5%
• Manganese (Mn): 2.0% max
• Silicon (Si): 0.75% max
• Phosphorus (P): 0.045% max
• Sulfur (S): 0.03% max

Grade 304 stainless steel is the mostly used and versatile stainless steel grade. It provides good corrosion resistance, excellent form-ability, and can be easily welded or formed into various shapes.

Grade 316 Stainless Steel

• Carbon (C): 0.08% max
• Chromium (Cr): 16.0-18.0%
• Nickel (Ni): 10.0-14.0%
• Molybdenum (Mo): 2.0-3.0%
• Manganese (Mn): 2.0% max
• Silicon (Si): 0.75% max
• Phosphorus (P): 0.045% max
• Sulfur (S): 0.03% max

Grade 316 stainless steel contains additional molybdenum, which enhances its corrosion resistance, particularly in environments with high chloride concentrations. It is commonly used in marine and coastal applications, as well as in industries where exposure to corrosive chemicals is a concern.

Both grades are austenitic stainless steels, meaning they have a face-centered cubic crystal structure, which helps  to make  excellent mechanical properties and corrosion resistance. These compositions are just a general representation, and there are various sub grades and variations of stainless steel with specific compositions tailored to meet different requirements.

Application of  Stainless steel pipe

• Plumbing: Stainless steel pipes are commonly used for water supply and drainage systems due to their corrosion resistance and hygienic properties.
• Oil and Gas: They are used in the transportation of oil, gas, and other fluids in various parts of the industry.
• Chemical and Petrochemical: Stainless steel pipes are used in chemical processing plants and refineries where they can handle corrosive chemicals and high-temperature environments.
• Food and Beverage: Stainless steel pipes are preferred in the food and beverage industry due to their hygienic properties and resistance to rust and contamination.
• Construction: They find use in structural applications and architectural elements, particularly where corrosion resistance is needed.
• Automotive: Some automotive exhaust systems are made of stainless steel because its has heat resistance and durability.

Stainless steel pipes come in various grades and sizes to meet different requirements. Common grades include 304 and 316, with 316 being more resistant to corrosion, particularly in environments with higher chloride concentrations (e.g., coastal areas). The choice of grade depends on the specific application and environmental conditions.

Stainless steel is immune to CO2 corrosion due to the formation of protective oxide film to prevent corrosion of the underlying metals. Two types of austenitic stainless steel are discussed here, i.e. austenitic stainless steel and highly alloyed austenitic stainless steel. Austenitic stainless steel includes type SS316, SS304. SS304 is not commonly used for marine
environment due to less chromium, nickel and molybdenum content which shows lower corrosion resistant than SS316. SS904 and SS6Mo are grouped under highly alloyed austenitic stainless steel which exhibit higher corrosion resistant.

Stainless steel SS316

SS316 is immune to CO2 corrosion. However, it is more susceptible to attack from the offshore marine environment. It is noted that SS316 material should have minimum 2.5% Mo to improve CISCC and pitting resistance of the material. However, in oxygen free environments and temperature below 60˚C, there has no problem of chloride pitting and cracking

SS316 is widely used on offshore installations when CRAs are required. The “L” type of SS316 has lower carbon content than the standard version of the alloy, typically maximum 0.03wt% compared to maximum 0.08 wt% for standard version. The lower carbon content gives better resistance towards sensitization during welding and heat treatment.

Stainless steel  SS904

SS904 is a material with chemistry between SS316 and SS6Mo. The corrosion resistance is comparable to DSS, except that resistance to H2S failure is equivalent to SS316. The austenitic microstructure enables the material to be used to low temperatures. Typical applications will be cladding material for vessels, where a more robust material than SS316 is required, and vessels, where resistance to both high and low temperature is required. SS904 will offer a cost effective material selection to SS6Mo.

Stainless steel SS6Mo

Highly alloyed austenitic stainless steel, SS6Mo has a corrosion resistance in seawater comparable to SDSS; both may be used in piping systems up to 20˚C without problems. SS6Mo is however significantly more costly due to relatively higher alloy elements such as nickel and molybdenum. One advantage of SS6Mo compared to SDSS in seawater is however better resistance towards hydrogen induced stress corrosion cracking (HISC) when exposed to cathodic protection. SS6Mo has, like all other austenitic materials, good low temperature properties. It is commonly used for systems where both low and high temperature may occur, and where SS316L cannot be used due to sour service restriction.

Stainless steel pipe wall thickness chart