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Stainless Steel 316, 316L, 316H,

Often referred to as "Marine Grade" stainless steel it has very similar physical properties to 304 and can be used in fabrication in much the same way. However, by including molybdenum in its formulation it has increased corrosion resistance particularly against "pitting corrosion". The major cause of pitting corrosion is the presence of chlorides, hence the need for enhanced resistance in the marine environment.

Stainless steel 316 is an austenitic steel with excellent welding and forming characteristics. It is the second most commonly used stainless steel and represents around 20% of the entire world production of stainless steel.

The key element that differentiates it from most other stainless steels is the inclusion of molybdenum, between 2% and 3%, which enhances its resistance corrosion in general and pitting corrosion in particular.

It is malleable and ductile and has good weldability. Its austenitic structure allows it to be deep drawn without intermediate annealing. It is also unnecessary to anneal it following welding thin sections.

However, the inclusion of molybdenum may have some adverse effects on its formability.

It is widely used in:

  • Chemical processing and storage equipment.
  • Refinery equipment
  • Medical devices
  • Marine environments, especially those with chlorides present

In its annealed state it is virtually non-magnetic even when cold worked, unlike 304 which can be significantly attracted to a magnet after cold working. This may make it more suitable in some applications.

The range of properties of 316 make it second only to 304 in quantity used and it is employed in many industries.

It is a good choice for architectural applications in coastal areas where there may be a significant amount of salt in the atmosphere however it is more expensive than 304 and is unnecessary away from the coast. Onboard seagoing vessels it is the natural choice for steel fittings whether on-deck or below.

It should also be considered for use in cold climates where significant amounts of de-icing salt is used on the roads. In these environments the level of salt in the atmosphere can be much higher than that found in coastal areas.

The combination of greater corrosion resistance and good formability make it a good choice food and beverage processing equipment; hot water systems; and plant for chemical, petrochemical, mineral processing if chlorides are likely to be present.

It should, however, be borne in mind that it is not as easily machined as other austenitic steels.

Corrosion Resistance

The major benefit of 316 is its increased corrosion resistance.  In addition to its resistance to chlorides it is also highly resistant to sulfuric, and sulfurous acids, acetic acid, as well as many industrial chemicals and solvents. These types of corrosive process chemicals are used to make a wide variety of products including inks, textiles, photographic chemicals, paper, textiles, rubber, and bleaches.

You should be aware that there are limitations to 316's corrosion resistance and if it is being used in hostile environments care should be taken. It is generally safe to use in the offshore industry in northern European waters this is regarded as the maximum temperature at which it is safe to use for prolonged exposure to seawater. 

The UK HSE has produced an excellent paper on the selection of stainless steels for the offshore industry. Click here.

Heat Resistance

316 resists oxidation well in intermittent exposure to temperatures up to 870oC and in continuous exposure to temperatures to 925oC.

It is not recommended for use in the 425oC to 860oC range if resistance to aqueous corrosion is required.

If there is a danger of intergranular corrosion 316L, the lower carbon form, is more resistant to carbide precipitation and should be considered. 

316H provides greater strength at higher temperatures and is often used in high-pressure applications above 500oC. If there is a need to provide increased resistance to chlorides you should consider 316Ti. The addition of titanium results in the forming of titanium carbides rather than chromium carbide resulting in better resistance to intergranular corrosion.

The major drawback of 316 over 304 stainless steel is the increased cost - generally about 20% to 25% higher. However, when considering cost the "whole-life" cost should be calculated and the increased corrosion resistance of 316 may result in it producing a considerable saving.

Stress Corrosion Cracking

Austenitic stainless steels can be subject to stress corrosion cracking but 316 is generally more resistant particularly at ambient temperatures. However, there have been some curious examples of stress corrosion cracking that are worth bearing in mind.

In continuously high humidity environments in the presence of halides stress corrosion cracking at ambient temperatures has been noted. at least one swimming pool roof has collapsed as a consequence.

It should be emphasised the the production of a good surface finish and good welding techniques do much to reduce the vulnerability of all forms of corrosion.

The main constituents of 316 stainless steel - other than iron - are Chromium and Nickel. However, it is the addition of 2% Molybdenum that provides the increased corrosion resistance.

316 contains 16 - 18% Chromium (Cr). Chromium is the essential chemical in all stainless steel and it is that which forms the thin passive layer that makes the metal "stainless"

316 also contains 10-14% Nickel (Ni). This is added to make the Austenitic structure more stable at normal temperatures. 

The nickel also improves high-temperature oxidation resistance makes the steel resistant to stress corrosion cracking.

Where the steel is to be stretched formed a lower percentage (8%) of nickel should be selected. If the steel is to be deep drawn a higher percentage is better (9% or more).

In addition a number of other chemicals may be present but these are expressed as maximum permited levels with the exception of the increased quantity of carbon required in 316H - i.e. a minimum of .04% and a maximum of 0.10%

GradeCMnSiPSCrMoNiN
316 min.
max.
-
0.08
-
2.0
-
0.75
-
0.045
-
0.030
16.0
18.0
2.0
2.0
10.0
14.0
-
0.10
316L min.
max.
-
0.030
-
2.0
-
0.75
-
0.045
-
0.030
16.0
18.0
2.0
2.0
10.0
14.0
-
0.10
316H min.
max.
0.04
0.10
-
2.0
-
0.75
-0.045 -
0.030
16.0
18.0
2.0
2.0
10.0
14.10
-

Physical Properties

 

Metric

English

Density

8 g/cc

0.289 lb/in³

               

Mechanical Properties

Hardness, Brinell

123

123

Converted from Rockwell B hardness.

Hardness, Knoop

138

138

Converted from Rockwell B hardness.

Hardness, Rockwell B

70

70

 

Hardness, Vickers

129

129

Converted from Rockwell B hardness.

Tensile Strength, Ultimate

505 MPa

73200 psi

 

Tensile Strength, Yield

215 MPa

31200 psi

at 0.2% offset

Elongation at Break

70 %

70 %

in 50 mm

Modulus of Elasticity

193 - 200 GPa

28000 - 29000 ksi

 

Poisson's Ratio

0.29

0.29

 

Charpy Impact

325 J

240 ft-lb

 

Shear Modulus

86 GPa

12500 ksi

 

Electrical Properties

Electrical Resistivity

7.2e-005 ohm-cm

7.2e-005 ohm-cm

at 20°C (68°F); 1.16E-04 at 650°C (1200°F)

Magnetic Permeability

1.008

1.008

at RT

Thermal Properties

CTE, linear 20°C

17.3 µm/m-°C

9.61 µin/in-°F

from from 0-100°C

CTE, linear 250°C

17.8 µm/m-°C

9.89 µin/in-°F

at 0-315°C (32-600°F)

CTE, linear 500°C

18.7 µm/m-°C

10.4 µin/in-°F

at 0-650°C

Specific Heat Capacity

0.5 J/g-°C

0.12 BTU/lb-°F

from 0-100°C (32-212°F)

Thermal Conductivity

16.2 W/m-K

112 BTU-in/hr-ft²-°F

at 0-100°C, 21.5 W/m°C at 500°C

Melting Point

1400 - 1455 °C

2550 - 2650 °F

 

Solidus

1400 °C

2550 °F

 

Liquidus

1455 °C

2650 °F

 

The two main variants of grade 316 are the low carbon form 316L and the high carbon form 316H

316L has a maximum of 0.30% carbon. This reduces the tendency for carbide precipitation when welding. Carbide precipitation can result in intergranular corrosion.

316H has between 0.04 and 0.1% carbon. This gives it greater strength at high temperature but does make it more vulnerable to carbide precipitation when welding.

If avoidance of carbide precipitation is important then the use of 316Ti, which has Titanium added to it, may be the answer. The titanium combines with the carbon forming titanium carbides, in preference to the chromium preserving the passive layer.

In common with 304, 316 has a maximum of 0.08% carbon, there are potential overlaps in the specifications which means that it is not uncommon to find dual specification. 

316L having less than 0.08% carbon it can, therefore, be described as 316/316L.

316 may have up to 0.08% carbon so if its carbon content is between 0.04 and 0.08% carbon it may be described as 316/316H.

Stainless 316, 316H, 316L Forms Available

  • Tube
  • Pipe
  • Fittings
  • Flanges
  • Special Sections
  • Sheet
  • Plate
  • Flat Bar
  • Round Bar
  • Hollow Bar
  • Angles
  • i Beam
  • U Channel

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