Stainless steel 317L and 317LMN

317LMN and 317L are austenitic stainless steel containing molybdenum. Compared with ordinary chrome-nickel austenitic stainless steel (such as 304 stainless steel), its resistance to chemical erosion better, high temperature environment, the fracture stress intensity stronger, better ductility. The combination of molybdenum and nitrogen improves the pitting resistance and resistance to pitting of stainless steels, especially in high temperature environments containing acidic compounds, chlorides and sulfides. Nitrogen while improving the strength of stainless steel.

Chemical Composition

The chemical composition of grade 317L stainless steel is outlined in the following table.

Element

Content (%)

Iron, Fe

Balance

Chromium, Cr

18-20

Nickel, Ni

11-15

Molybdenum, Mo

3-4

Manganese, Mn

2

Silicon, Si

1

Phosphorous, P

0.045

Carbon, C

0.03

Sulfur, S

0.03

Corrosion resistance of stainless steel

317L and 317LMN stainless steel withstand the atmosphere and mild corrosive ability, in addition to strong oxidizing acid (such as nitric acid).

317LMN and 317L stainless steel anti-sulfuric acid solution corrosion better. Its corrosion resistance increases with the increase of molybdenum content of stainless steel. These stainless steels can withstand up to 5% sulfuric acid at temperatures up to 120 ° F (49 ° C). At temperatures below 100 ° F (38 ° C), these stainless steels have excellent corrosion resistance and are resistant to higher concentrations of solution corrosion. However, application testing should take into account specific operating factors that may affect corrosion behavior. These stainless steels are more resistant to the formation of concentrated gases than conventional stainless steel 316 during the process of concentration of sulfur-containing gases. The concentration of acid has a significant effect on the corrosion rate in such an environment and should be carefully determined according to the specific application test.

The following table shows the corrosion resistance of annealed 317LMN and 317L samples in a variety of solutions, all of which are related to the processing industry and ASTM testing. This table lists the relevant data for stainless steel 316L and stainless steel AL276 for comparison.

Corrosion Resistance in Boiling Solutions and ASTM Tests

Test Solution

Corrosion Rate in Mils per Year (mm/y)  for Cited Alloys

Alloy 316L

Alloy 317L

Alloy 317LMN

Alloy 276

20% Acetic Acid

0.12 (<0.01)

0.48 (0.01)

0.12 (<0.01)

0.48 (0.01)

45% Formic Acid

23.41 (0.60)

18.37 (0.47)

11.76 (0.30)

2.76 (0.07)

10% Oxalic Acid

48.03 (1.23)

44.90 (1.14)

35.76 (0.91)

11.24 (0.28)

20% Phosphoric Acid

0.06 (0.02)

0.72 (0.02)

0.24 (<0.01)

0.36 (0.01)

10% Sulfuric Acid

635.7 (16.15)

298.28 (7.58)

157.80 (4.01)

13.93 (0.35)

10% Sodium Bisulfate

71.57 (1.82)

55.76 (1.42)

15.60 (0.40)

2.64 (0.07)

50% Sodium Hydroxide

77.69 (1.92)

32.78 (0.83)

85.68 (2.18)

17.77 (0.45)

ASTM A262 Practice B (FeSO4H2SO4)

26.04 (0.66)

20.76 (0.53)

17.28 (0.44)

264.5 (6.72)

ASTM A262 Practice C (65% HNO3)

22.31 (0.56)

19.68 (0.50)

16.32 (0.42)

908.0 (23.06)

ASTM A262 Practice E (Cu•CUSO4•H2SO4)

Pass

Pass

Pass

Pass

The low carbon (less than 0.03%) of these alloys effectively prevents sensitization to intergranular corrosion during thermal processes such as welding or forging. The higher chromium contents of 317LMN and Alloy 317L stainless steels also provide superior resistance to intergranular attack. It should be noted that prolonged exposure in the range 800 to 1400°F (427-816°C) can be detrimental to intergranular corrosion resistance and may also cause embrittlement due to precipitation of sigma phase. The higher nitrogen content of the 317LMN alloy retards the precipitation of sigma phase as well as carbides.

Pitting Resistance Equivalents

Alloy

PRE

Alloy 316

25

Alloy 317L

30

Alloy 317LMN

38

Alloy 625

52

Alloy C276

69

High molybdenum and nitrogen contents can significantly improve pitting resistance as illustrated in the preceding table of Pitting Resistance Equivalents (PRE). The PRE is based on the results of corrosion tests in which it was found that nitrogen was 30 times more effective than chromium and approximately 9 times more effective than molybdenum in enhancing chloride pitting resistance.

The temperature of the onset of crevice corrosion as determined in a modified AST G-48B test is a useful means of ranking the relative resistance of stainless and nickel-base alloys. The Critical Crevice Corrosion Temperatures table that follows demonstrates that crevice corrosion resistance for austenitic stainless steel tubing increases with the alloy’s molybdenum and nitrogen content.

Crevice Corrosion in a Simulated  FGD System Environment

Alloy

Weight Loss (g/cm2)  for Tests* at Cited Temperatures

24°C (75°F)

50°C (122°F)

70°C (158°F)

Alloy 317L

0.0007

0.0377

0.0500

Alloy 317LMN

0.0000

0.0129

0.0462

Alloy 625

0.0000

0.0000

0.0149

Alloy C276

0.0000

0.0001

0.0004

*72-hour exposure based on ASTM G-48B procedure using the following solution:  7 vol.%H2SO4, 3 vol%HCI, 1 wt% CuCl2, 1 wt%FeCl3

Mechanical Properties

The mechanical properties of grade 317L stainless steel are displayed in the following table.

Properties

Metric

Imperial

Tensile strength

595 MPa

86300 psi

Yield strength

260 MPa

37700 psi

Modulus of elasticity

200 GPa

29000 ksi

Poisson’s ratio

0.27-0.30

0.27-0.30

Elongation at break (in 50 mm)

55%

55%

Hardness, Rockwell B

85

85

Antioxidant properties

Chromium-nickel-molybdenum steel has excellent oxidation resistance, and in the ordinary atmosphere, the temperature is not higher than 1600-1650 ° F (871-899 ° C), the scale generation rate is low.

Stainless steel processing performance

317LMN stainless steel and 317L stainless steel physical and mechanical properties and conventional austenitic stainless steel similar, therefore, can be processed 304 stainless steel and 316 stainless steel method for its processing.

Manufacturing Process

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.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.

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.

Grade 317L stainless steel does not respond to heat treatment.

Applications

Grade 317L stainless steel is widely used in the following applications:

· Condensers in fossil

· Pulp and paper manufacturing

· Nuclear fueled power generation stations

· Chemical and petrochemical process equipment.

Source: wilsonpipeline Pipe Industry (www.wilsonpipeline.com)