316/316L Stainless Steel, 316L Stainless Steel, Stainless pipe

Electropolished seamless tube

What do the AP, MP, BA and EP standards of stainless steel pipes mean?

The terms AP, MP, BA, and EP refer to different surface finishes or treatments applied to the stainless steel.

These finishes are essential in various industries where the appearance, corrosion resistance, and cleanliness of the stainless steel are critical. Here's an explanation of each term:

EP (Electropolished): EP stands for electropolished, a process where the stainless steel tube, after annealing and acid pickling, undergoes electropolishing using electrodes and acid in a tank, creating a chemical reaction to achieve a clean surface through electrochemical polishing. EP tubes are used in pipeline projects with high cleanliness requirements for the stainless steel tube surface.

AP (Annealed and Pickled): AP refers to the condition where the surface of the stainless steel tube is treated after annealing through acid pickling to remove the oxide layer. Stainless steel industrial pipes sold in the market, known for their wide applications, are extensively used in the chemical industry for pipeline needs.

MP (Mechanical Polished): MP denotes a stainless steel seamless tube that undergoes mechanical polishing after annealing and acid pickling to achieve a bright and clean surface. This finish is primarily utilized in the pharmaceutical and food industries.

BA (Bright Annealed): BA is specific to precision-rolled stainless steel tubes. Also known as precision tubes, BA tubes skip the regular annealing and acid pickling process after semi-finished rolling. Instead, they use argon gas in a vacuum annealing furnace to remove surface oil stains generated during the rolling process, preserving the brightness of the surface without leaving an oxide layer.

These surface finishes cater to various industry requirements, offering different levels of brightness, cleanliness, and corrosion resistance based on specific applications.

Properties

Alloy 316/316L is an austenitic alloy and similar to 304/304L is used in a wide range of applications. It is an important alloy when it comes to chloride environments and many other chemical process industries. The addition of Molybdenum significantly increases general corrosion resistance as compared to 304/304L and more importantly, increases the chloride pitting resistance.

316/316L has excellent forming and welding characteristics. Due to its superior chloride pitting resistance, it is commonly used in applications involving chlorides or halides. That property is also useful in marine environments.

It also has an excellent resistance to intergranular corrosion in as-welded condition. Dual grade becomes important if heavy gauge welding is performed. This is where intergranular corrosion comes into picture and having a lower carbon version makes it difficult for Chromium Carbide to precipitate in the 797 to 1580 degF (425 to 860 degC) range when the welding is going on for a long time due to the heavy gauge.

It has excellent creep and rupture strength at higher temperatures compared to 304/304L. Finally, it has excellent strength and toughness at cryogenic temperatures.

Applications

Very wide ranging. It is practically used almost everywhere:

marine industry
chemical process vessels
heat exchangers
food and wine industry
pharmaceutical industry
water treatment
petroleum refining
etc.

In addition, it provides excellent elevated temperature tensile, creep and stress-rupture strengths.

Chemcial Composition - 316/316L stainless steel tubing and pipe

Grade	316	316L
UNS Designation	S31600	S31603
Carbon (C) Max.	0.08	0.030*
Manganese (Mn) Max.	2.00	2.00
Phosphorous (P) Max.	0.045	0.045
Sulphur (S) Max.	0.030	0.030
Silicon (Si) Max.	1.00	1.00
Chromium (Cr)	16.0 – 18.0	16.0 – 18.0
Nickel (Ni)	10.0 – 14.0	10.0 – 14.0
Molybdenum (Mo)	2.0 – 3.0	2.0 – 3.0
Nitrogen (N)	—	—
Iron (Fe)	Bal.	Bal.
Other Elements	—	—

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%

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

Typical Mechanical Properties- Stainless Steel 316/316L

Material	Form	Tensile Strength (ksi)	Yield Strength (ksi)	Elongation %	Hardness HB
Alloy 316L	316L Sheet AMS 5507	100 max	-	45	-
Alloy 316	316 Sheet AMS 5524	75 min	30	45	207 max

Physical Properties - 316/316L/316H stainless steel in the Annealed Condition at -20°F to +100°F

Alloy	UNS Design -ation	Spec.	Tensile Strength			Yield Strength
Alloy	UNS Design -ation	Spec.	psi	MPa	ksi	psi	MPa	ksi	Elongation in 2 inches (min.) %	Grain Size Req.	Max. Hardness	Modulus of Elasticity (x106 psi)	Mean Coefficient of Thermal Expansion (IN./IN./°F x 10-6)	Thermal Conductivity (BTU-in/ft2-h-°F)
316	S31600	A249, A312	75,000	515	75	30,000	205	30	35	—	90 Rb	28.0	9.2	116
316L	S31603	A270, A312	70,000	485	70	25,000	170	25	—	—	90 Rb	28.0	9.2	116
316H	S31609	—	—	—	—	—	—	—	—	7 or coarser	—	—	—	—

Product Range - 316/316L Stainles steel

Alloy	UNS Designation	Werkstoff NR.	Specifications*
316	S31600	1.4401	A269, A/SA249, A/SA312, A1016, A632, A/SA688
316L**	S31603	1.4404	A269, A/SA249, A/SA312, A1016, A632, A/SA688

*Note: The specifications noted including ASTM, ASME, or other applicable authorities are correct at the time of publication. Other specifications may apply for use of these materials in different applications.

Type 316 is more resistant to atmospheric and other mild environments than Type 304. it is resistant to dilute solutions (i.e. 1-5%) of sulfuric acid up to 120°F. However, in certain oxidizing acids, Type 316 is less resistant than Type 304.
316 is susceptible to carbide precipitation when exposed in the temperature range of 800° - 1500°F and therefore is susceptible to intergranular corrosion in the as-welded condition. Annealing after welding will restore corrosion resistance.
Type316L has the same composition as Type 316 except the carbon content is held below 0.03%. Not unexpectedly, its general corrosion resistance and other properties closely correspond to those of Type 316. However, it does provide immunity to intergranular attack in the as-welded condition or with short periods of exposure in the temperature range of 800° - 1500°F. The use of 316L is recommended when exposure in the carbide precipitation range is unavoidable and where annealing after welding is not practical. However, prolonged exposure in this range may embrittle the material and make it susceptible to intergranular attack.
The maximum temperature for scaling resistance in contnuous services is about 1650°F, and 1500°F for intermittent service.
May be susceptible to chloride stress corrosion cracking.
Non-hardenable; non-magnetic in the annealed condition, and slightly magnetic when cold worked.
Improved corrosion resistance to chlorides.

Typical Applications - Stainless Steel 316/316L

Nuclear
Chemical Processing
Rubber
Plastics
Pulp & Paper
Pharmaceutical
Textile
Heat exchangers, condensers & evaporators

Tensile Requirements - Stainless Steel 316/316L

Tensile Strength (KSI): 70

Yield Strength (KSI): 25

KSI can be converted to MPA (Megapascals) by multiplying by 6.895.

316L

Type 316L is the low carbon version of 316 stainless. With the addition of molybdenum, the steel is popular for use in severe corrosion environments due to the materials immunity from boundary carbide precipitation (sensitisation).

The material is widely used in heavy gauge welded components and weld annealing is only required where the material is for use in high stress environments. 316L has an extensive variety of uses especially in marine applications due to the materials high corrosion resistance.

Benefits of using Type 316L Stainless Steel

Low carbon content eliminates carbon precipitation in the welding process
Can be used in severe corrosive environments
Improved anti–corrosion scope due to added Molybdenum
Weld annealing only required in high stress applications
Very similar to Grade 316 in chemical composition and mechanical properties

316H

Type 316H is a higher carbon variant of 316 making the steel more suitable for use in applications where elevated temperatures are present.

Stabilised Grade 316Ti offers similar qualities.

The increased carbon content delivers a greater tensile and yield strength. The austenitic structure of the material also gives this grade excellent toughness, even down to cryogenic temperatures.