Called Duplex Pipe because of its mixed microstructure with about equal proportions of ferrite and austenite, duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content. The chemical composition based on high contents of Cr and Mo, improves intergranular and pitting corrosion resistance, respectively. Additions of nitrogen can promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventional stainless steels.
Duplex is a stainless steel made from a mixture of austenite and ferrite phases. Like most austenitic stainless steels, duplex has a strong resistance to corrosion, similar to those of a Type 304 and 316.
Unlike similar steels, duplex also displays an improved resistance to localized corrosion, particularly pitting, crevice corrosion and stress corrosion cracking. And because duplex has a lower nickel and molybdenum content than other austenitic stainless steels, it can prove a more cost effective option due to a lower alloying content.
Due to its Ferritic qualities, duplex steel also shows very good resistance to stress corrosion cracking when compared to standard austenitic. In some cases, the strength of duplex steel can be up to double that of the most commonly used grades of stainless steel.
Duplex becomes brittle at extreme temperatures so its use is normally restricted to a maximum temperature of 300 degrees. Duplex also shows signs of embrittlement at –50 degrees.
Stronger than 300 series stainless steel which also brings weight advantages.
Cheaper than some stainless steels.
High resistance to pitting, crevice corrosion and stress corrosion cracking.
Higher heat conductivity and lower thermal expansion than austenitic steels.
Pipes for production and transportation of oil and gas
Structural and mechanical components
Heat exchangers
Cooling pipes
Cargo vessels and containers
High strength wiring
1. Scope*
1.1 This specification2 covers seamless and straight-seam welded ferritic/austenitic steel pipe intended for general corrosive service, with particular emphasis on resistance to stress corrosion cracking. These steels are susceptible to embrittlement if used for prolonged periods at elevated temperatures.
1.2 Optional supplementary requirements are provided for pipe when a greater degree of testing is desired. These supplementary requirements call for additional tests to be made and, when desired, one or more of these may be specified in the order.
1.3 Appendix X1 of this specification lists the dimensions of welded and seamless stainless steel pipe as shown in ANSIB36.19. Pipe having other dimensions may be furnished
provided such pipe complies with all other requirements of this specification.
1.4 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification. The inch-pound units shall apply unless the M designation of this specification is specified in the order.
2.1 ASTM Standards: 3
A 370 Test Methods and Definitions for Mechanical Testing of Steel Products
A 941 Terminology Relating to Steel, Stainless Steel, Related Alloys and Feroalloys
A 999/A 999M Specification for General Requirements for Alloy and Stainless Steel Pipe
E 213 Practice for Ultrasonic Examination of Metal Pipe and Tubing
E 309 Practice for Eddy-Current Examination of Steel Tubular Products Using Magnetic Saturation
E 381 Method of Macroetch Testing Steel Bars, Billets, Blooms, and Forgings
E 426 Practice for Electromagnetic (Eddy-Current) Examination of Seamless and Welded Tubular Products, Austenitic Stainless Steel and Similar Alloys
E 527 Practice for Numbering Metals and Alloys (UNS)
2.2 ANSI Standards:4
B1.20.1 Pipe Threads, General Purpose
B36.10 Welded and Seamless Wrought Steel Pipe
B36.19 Stainless Steel Pipe
2.3 SAE Standard:5
SAE J 1086
2.4 Other Standard:6
SNT-TC-1A Personal Qualification and Certification in Nondestructive Testing
4.1 Orders for material under this specification should include the following, as required, to describe the desired material adequately:
4.1.1 Quantity (feet, metres, or number of lengths),
4.1.2 Name of material (ferritic/austenitic steel pipe),
4.1.3 Process (seamless or welded),
4.1.4 Grade (see Table 1),
4.1.5 Size (NPS designator or outside diameter and schedule number of average wall thickness),
4.1.6 Length (specific or random) (see Section 11),
4.1.7 End finish (section on ends of Specification A 999/A 999M),
4.1.8 Optional requirements (product analysis, Section 9;hydrostatic test or nondestructive electric test, Section 14),
4.1.9 Test report required (section on certification of SpecificationA 999/A 999M),
4.1.10 Specification designation, and
4.1.11 Special requirements and any supplementary requirementsselected.
Material furnished under this specification shall conform to the applicable requirements of the current edition of Specification A 999/A 999M unless otherwise provided herein
|
UNS Designation |
Tensile Strength,
min, ksi[MPa]
|
Yield Strength,
min, ksi [MPa]
|
Elongation in 2 in. or 50 mm,min, % |
Hardness, max |
|
|
Brinell |
HRC |
||||
|
S31803 |
90 [620] |
65 [450] |
25 |
290 |
30 |
|
S32205 |
95 [655] |
70 [485] |
25 |
290 |
30 |
|
S31500 |
92 [630] |
64 [440] |
30 |
290 |
30 |
|
S32550 |
110 [760] |
80 [550] |
15 |
297 |
31 |
|
S31200 |
100 [690] |
65 [450] |
25 |
280 |
- |
|
S31260B |
100 [690] |
65 [450] |
25 |
290 |
30 |
|
S32001 |
90 [620] |
65 [450] |
25 |
290 |
30 |
|
S32304 |
|||||
|
OD 1 in. [25 mm] and Under |
100 [690] |
65 [450] |
25 |
- |
- |
|
OD over 1 in. [25 mm] |
87 [600] |
58 [400] |
25 |
290 |
30 |
|
S39274 |
116 [800] |
80 [550] |
15 |
310 |
- |
|
S32750 |
116 [800] |
80 [550] |
15 |
300 |
32 |
|
S32760 |
109 [750] |
80 [550] |
25 |
300 |
- |
|
S32900 |
90 [620] |
70 [485] |
20 |
271 |
28 |
|
S32950C |
100 [690] |
70 [480] |
20 |
290 |
30 |
|
S39277 |
120 [825] |
90 [620] |
25 |
290 |
30 |
|
S32520 |
112 [770] |
80 [550] |
25 |
310 |
- |
|
S32906 |
|||||
|
Wall below 0.40 in.(10 mm) |
116 [800] |
94 [650] |
25 |
300 |
32 |
|
Wall 0.40 in. (10 mm) and above |
109 [750] |
80 [550] |
25 |
300 |
32 |
|
S32003 |
90 [620] |
65 [450] |
25 |
290 |
30 |
A For tubing smaller than 1⁄2 in. [12.7 mm] in outside diameter, the elongation values given for strip specimens in Table 4 shall apply. Mechanical property
requirements do not apply to tubing smaller than 1⁄8 in. [3.2 mm] in outside diameter or with walls thinner than 0.015 in. [0.4 mm].
B Prior to A 789/A 789M–87, the values for S31260 were: 92 ksi tensile strength, 54 ksi yield strength, and 30 % elongation.
C Prior to A 789/A 789M–89, the tensile strength value was 90 ksi for UNS S32950.
|
UNS
Designation A
|
C |
Mn |
P |
S |
Si |
Ni |
Cr |
Mo |
N |
Cu |
Others |
|
S31803 |
0.030 max |
2.00 max |
0.030 max |
0.020 max |
1.00 max |
4.5–6.5 |
21.0–23.0 |
2.5–3.5 |
0.08–0.20 |
- |
- |
|
S32205 |
0.030 max |
2.00 max |
0.030 max |
0.020 max |
1.00 max |
4.5–6.5 |
22.0–23.0 |
3.0–3.5 |
0.14–0.20 |
- |
- |
|
S31500 |
0.030 max |
1.20–2.00 |
0.030 max |
0.030 max |
1.40–2.00 |
4.3–5.2 |
18.0–19.0 |
2.50–3.00 |
0.05–0.1 |
- |
- |
|
S32550 |
0.04 max |
1.50 max |
0.040 max |
0.030 max |
1.00 max |
4.5–6.5 |
24.0–27.0 |
2.9–3.9 |
0.10–0.25 |
1.50–2.50 |
- |
|
S31200 |
0.030 max |
2.00 max |
0.045 max |
0.030 max |
1.00 max |
5.5–6.5 |
24.0–26.0 |
1.20–2.00 |
0.14–0.20 |
- |
- |
|
S31260 |
0.030 max |
1.00 max |
0.030 max |
0.030 max |
0.75 max |
5.5–7.5 |
24.0–26.0 |
2.5–3.5 |
0.10–0.30 |
0.20–0.80 |
W 0.10–0.50 |
|
S32001 |
0.030 max |
4.00–6.00 |
0.040 max |
0.030 max |
1.00 max |
1.0–3.0 |
19.5–21.5 |
0.60 max |
0.05–0.17 |
1.00 max |
- |
|
S32304 |
0.030 max |
2.50 max |
0.040 max |
0.040 max |
1.00 max |
3.0–5.5 |
21.5–24.5 |
0.05–0.60 |
0.05–0.20 |
0.05–0.60 |
- |
|
S39274 |
0.030 max |
1.00 max |
0.030 max |
0.020 max |
0.80 max |
6.0–8.0 |
24.0–26.0 |
2.5–3.5 |
0.24–0.32 |
0.20–0.80 |
W 1.50–2.50 |
|
S32750 |
0.030 max |
1.20 max |
0.035 max |
0.020 max |
0.80 max |
6.0–8.0 |
24.0–26.0 |
3.0–5.0 |
0.24–0.32 |
0.50 max |
- |
|
S32760 |
0.05 max |
1.00 max |
0.030 max |
0.010 max |
1.00 max |
6.0–8.0 |
24.0–26.0 |
3.0–4.0 |
0.20–0.30 |
0.50–1.00 |
W 0.50–1.00
40 minB
|
|
S32900 |
0.08 max |
1.00 max |
0.040 max |
0.030 max |
0.75 max |
2.5–5.0 |
23.0–28.0 |
1.00–2.00 |
- |
- |
- |
|
S32950 |
0.030 max |
2.00 max |
0.035 max |
0.010 max |
0.60 max |
3.5–5.2 |
26.0–29.0 |
1.00–2.50 |
0.15–0.35 |
- |
- |
|
S39277 |
0.025 max |
0.80 max |
0.025 max |
0.002 max |
0.80 max |
6.5–8.0 |
24.0–26.0 |
3.00–4.00 |
0.23–0.33 |
1.20–2.00 |
W 0.80–1.21 |
|
S32520 |
0.030 max |
1.50 max |
0.035 max |
0.020 max |
0.80 max |
5.5–8.0 |
23.0–25.0 |
3.–5. |
0.20–0.35 |
0.50–3.00 |
- |
|
S32906 |
0.030 max |
1.50 max
0.80 min
|
0.030 max |
0.030 max |
0.50 max |
7.5 max
5.8 min
|
30.0 max
28.0 min
|
2.60 max
1.50 min
|
0.40
.30
|
0.80
-
|
-
-
|
|
S32003 |
0.030 max |
2.00 max |
0.030 max |
0.020 max |
1.00 max |
3.0-4.0 |
19.5-22.5 |
1.50-2.00 |
0.14-0.20 |
- |
- |
A New designation established in accordance with Practice E 527 and SAE J1086.
B % Cr + 3.3 3 %Mo + 16 3 % N.