316/316L STAINLESS VALVES

Valves are manufactured in ASTM A182 316/316L forgings and ASTM A351 CF8/CF3 castings. Trim components can also be in UNS S31600 and AISI-SAE 316/316L. Welded end valves can be in 316 but 316L is often preferred due to the lower carbon content which avoids inter granular corrosion in the as-welded state thereby providing superior corrosion resistance compared to 316. However 316 can be post-weld annealed to promote maximum corrosion resistance.

316 and 316L are molybdenum steels with enhanced resistance to pitting by solutions with chlorides and other halides. These grades offer tensile, creep and stress-rupture strength in higher-temperature applications. 316 and 316L offer better resistance to atmospheric and mild environments than 304 and 304L.

DESIGN FEATURES 316/316L

316 is resistant to dilute solutions (1-5%) of sulfuric acid to 49ºC (120ºF), except in some oxidising acids, where 316 is less resistant than 304.
316 is susceptible to inter granular corrosion in the as-welded condition
316 is prone to carbide precipitation from 427ºC to 816ºC (800ºF to 1500ºF)
Corrosion resistance can be restored by post-welding annealing
316L offers same composition but with less than 0.03% carbon
316L presents similar corrosion resistance and other characteristics as 316 but with added resistance to inter granular attack in the as-welded condition or with short exposures in the 427ºC to 816ºC (800ºF to 1500ºF) range
316L is appropriate in applications where it’s impossible to avoid exposure in the carbide precipitation range and when post-welding annealing isn’t practical; lengthy exposure in this range may make the material brittle and susceptible to inter granular attack
316 maximum temperature for scaling resistance is 899ºC (1650ºF) in continuous service and 816ºC (1500ºF) in intermittent service applications
316L has a slightly lower pressure rating at very high temperatures compared to 316
Susceptible to stress-corrossion cracking
Slightly magnetic in the cold-worked condition
Nonmagnetic and non harden able in the annealed condition
Enhanced resistance to chlorides

GRADE 316

After 304, 316 is the most common stainless steel on the market. It is an austenitic grade with the addition of 2-3% molybdenum which further improves corrosion resistance. It is often referred to as a marine grade stainless steel because of its effective resistance to chloride corrosion in comparison to other stainless steel grades.

The material has superior welding and forming qualities. Grade 316 will require post-weld annealing to promote maximum corrosion resistance, though this is not necessary if Type 316L is used.

APPLICATIONS OF GRADE 316 STAINLESS STEEL

Typical applications for this material are now widespread due to its superior corrosion resistance properties when compared to Grade 304. Type 316 stainless can be found in heat exchangers, pharmaceutical equipment, refineries, food industry, mining, process industries, etc.

316 & 316L steel valves have common properties and are often stocked by Global Supply Line with dual certification,where it is determined that both have properties and composition which comply with both steel types.

Type 316H is excluded from this overview but as a brief explanation, 316H is engineered to constantly work in even higher working temperatures than 316/316L. It should also be noted that 316L has a slightly lower maximum temperature rating and maximum cold working pressure rating than 316.

GRADE 316L

Type 316L is the low carbon version of 316 stainless. Again compared to 304/304L having the addition of molybdenum, the steel is popular for use in severe corrosion environments due to the materials immunity from boundary carbide precipitation (sensitisation) caused by welding.

Weld annealing is only required where the material is for use in high stress environments. 316L has an extensive variety of uses especially in highly corrosive applications.

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
Very similar to Grade 316 in chemical composition and mechanical properties
316 & 316L valves have common properties and are often stocked by Global Supply Line with dual certification, where it is determined that both have properties and composition which comply with both steel types.

The below tables are correct as per A182/A182M-13

CHEMICAL COMPOSITION

Grade C (MAX) Si (Max) Mn (Max) P (Max) S (Max) Cr Mo Ni N (Max)
316L 0.030 1.00 2.00 0.045 0.030 16.00/18.00 2.00/3.00 10.00/15.00 0.10
316 0.350 1.00 2.00 0.045 0.030 16.00/18.00 2.00/3.00 10.00/14.00 0.10

MECHANICAL PROPERTIES

Grade Yield Strength Tensile Strength Elongation (%) Reduction of Area (%) Hardness Max
Min (Mpa) Min (Mpa) Min Min (50mm) HB HR B
316L 170 485 30 50 217* 95*
316 205 515 30 50 217* 95*

* Maximum hardness not specified in ASTM A182/A182M-13