Advantages of 317L Stainless Steel

317L Stainless Steel Overview

317L Stainless Steel(or UNS S31703) is an austenitic alloy or SS with chromium-nickel-molybdenum content. Besides, 317L is famous for its low carbon corrosion resisting features. Due to its makeup content, it has high chloride pitting which makes its use in various industries perfect. The other names 317L is identified by in the industry include: ASTM A240, UNS S31703-317L, ASTM A182, ASME SA 240, ASTM A167. Alloy 317L is a molybdenum containing, low carbon austenitic stainless steel with increased additions of chromium, nickel, and molybdenum for better corrosion resistance and increased resistance to chemical attack for sulfurous, acetic, formic, citric, and tartaric acids. Due to its low carbon content, 317L Stainless Steel also provides resistance to sensitization when welded and higher creep, stress to rupture, and tensile strength at elevated temperatures. It is non-magnetic in the annealed condition but may become slightly magnetic after welding.

317L Stainless Steel has excellent corrosion resistance in a wide range of chemicals, especially in acidic chloride environments such as those encountered in pulp and paper mills. Increased levels of chromium, nickel and molybdenum compared to 316L stainless steel improve resistance to chloride pitting and general corrosion. Resistance increases with molybdenum alloy content. 317L Stainless Steel is resistant to sulfuric acid concentrations up to 5 percent at temperatures as high as 120°F (49°C). At temperatures under 100°F (38°C) this alloy has excellent resistance to solutions of higher concentration.

However, service tests are recommended to account for the affects of specific operating conditions that may affect corrosion behavior. In processes where condensation of sulfur-bearing gases occurs, 317L Stainless Steel is much more resistant to attack at the point of condensation than conventional alloy 316. The acid concentration has a marked influence on the rate of attack in such environments and should be carefully determined by service tests.

Chemical Properties

With 20% chromium, 11 – 15% nickel, 3 – 4% molybdenum, including iron (balanced level), and more, the chemical composition of 317L Stainless Steel is indeed a strong one. Other elements found in 317L include manganese 2%, 0.03% sulfur and carbon mixture, 1% silicon, and 0.045% phosphorus.

Due to the above details, they come with these chemical features:

• Rusting and corrosion. Since it has high quantities of molybdenum, it doesn’t corrode or rust easily.

• Resistant to various acidic environments. To many chemicals, 317L alloy is resistant. These include acidic chlorine, sulfuric acid, and phosphorus acid.

• Pitting and crevice corrosion. 317L alloy even with pitting and crevice doesn’t corrode at all.

• It also comes with the very best welding features. However, oxyacetylene welding method needs to be prevented.

What are the characteristics of 317L Stainless?

Alloy 317L is a low-carbon, high molybdenum austenitic stainless steel with a higher nickel alloy content than 316L. Developed to resist the attack of sulfuric acid compounds, this alloy combines good corrosion resistance with excellent mechanical properties and ease of fabrication.  These alloys are frequently used for flue gas desulfurization services in fossil-fuel power plants.  Compared to other austenitic stainless steels, 317L offers a higher creep strength, stress to rupture, and tensile strength at elevated temperatures.

Manufacturing Process

Machining stainless steel grade 317L requires low speeds and constant feeds to reduce its tendency to work harden. This steel is tougher than grade 304 stainless steel with a long stringy chip; however, using chip breakers is recommended. Welding can be performed using most of the conventional fusion and resistance methods. Oxyacetylene welding should be avoided. AWS E/ER 317L filler metal is recommended. Conventional hot working processes can be performed. The material should be heated to 1149-1260°C (2100-2300°F); however, it should not be heated below 927°C (1700°F). To optimize corrosion resistance, a post-work annealing is recommended. Shearing, stamping, heading and drawing are possible with grade 317L stainless steel, and post-work annealing is recommended to eliminate internal stresses. Annealing is performed at 1010-1121°C (1850-2050°F), which should be followed by rapid cooling.

Corrosion Resistance

Alloy 317L has excellent corrosion resistance to a wide range of chemicals. It resists attack in sulfuric acid, acidic chlorine and phosphoric acid. It is used in handling hot organic and fatty acids often present in food and pharmaceutical processing applications. The corrosion resistance of 317 and 317L should be the same in any given environment. The one exception is where the alloy will be exposed to temperatures in the chromium carbide precipitation range of 800 – 1500°F (427 – 816°C). Because of its low carbon content, 317L is the preferred material in this service to guard against intergranular corrosion.

In general, austenitic stainless steels are subject to chloride stress corrosion cracking in halide service. Although 317L is somewhat more resistant to stress corrosion cracking than 304/304L stainless steels, because of its higher molybdenum content, it is still susceptible. The higher chromium, molybdenum and nitrogen content of 317L enhance its ability to resist pitting and crevice corrosion in the presence of chlorides and other halides. The Pitting Resistance Equivalent including Nitrogen number (PREN) is a relative measure of pitting resistance.

Machinability

Grade 317L stainless steel is tougher than 304 stainless steel. It is recommended to use chip breakers. Hardenability of this alloy will be reduced if constant feeds and low speeds are used. It is a chromium-nickel-molybdenum stainless with low carbon (0%) content. The low carbon content combined with high chromium/nickel/molybdenum amount results in soft material with high resistance to machining and a low machinability rating of 38%.

The main challenge in machining austenitic stainless is the low carbon content combined with high chromium/nickel content. The result is a soft material with high resistance to machining. Because of the high ductility, you should generally opt for a sharp and positive cutting edge. In turning operations, one of the most common reasons for short tool-life is notch wear forming at the depth of the cut line, which results in a large burr forming on the workpiece. The best method to prevent notch wear is to change the depth of the cut constantly.

Welding

Grade 317L stainless steel can be welded using fusion and resistance methods. Oxyacetylene welding method is not preferred for this alloy. AWS E/ER317 or 317L filler metal can be used to obtain good result. 317L is a molybdenum bearing, low carbon content "L" grade austenitic stainless steel that provides improved corrosion resistance over 304L and 316L stainless steels. The low carbon provides resistance to sensitization during welding and other thermal processes. 317L is non-magnetic in the annealed condition but may become slightly magnetic as a result of welding.

Hot Working

Grade 317L stainless steel can be hot worked using all common hot working procedures. It is heated at 1149-1260°C (2100-2300°F). It should not be heated below 927°C (1700°F). Post-work annealing can be done to retain the corrosion resistance property.

Cold Working

Stamping, shearing, drawing, and heading can be done successfully. Post-work annealing is performed in order to reduce internal stress.

In what applications is 317L Stainless used?

Alloy 317L is commonly used to handle sulfur, pulp liquor, acid dyestuffs, acetylating and nitrating mixtures, bleaching solutions, severe coal and oil, and many chemical compounds. Some other applications that use alloy 317L include:

1. Paper and pulp handling equipment

2. Chemical and petrochemical processing equipment

3. Condensers in fossil and nuclear fueled power generation stations

4. Food processing equipment

5. Textile equipment

6. Air Pollution Control — flue gas desulfurization systems (FGD)

7. Explosives

8. Petroleum Refining