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UNS 32750 Dupex Stainless Steel Seamless Pipes & Tubes

Super Duplex Stainless Steel is a highly alloyed, good performance Duplex steel with a pitting resistance. Super Duplex offers good resistance to pitting and crevice corrosion. Super Duplex is suited for use in aggressive environments. Super Duplex Stainless has good resistance to stress corrosion cracking in chloride and sour environments. Super Duplex has good resistance to erosion corrosion and corrosion fatigue.

Super Duplex stainless like Duplex, is a mixed microstructure of austenite and ferrite (50/50) which has improved strength over ferritic and austenitic steel grades. The main difference is that Super duplex has a higher Molybdenum and Chromium content which gives the material greater corrosion resistance.

Super Duplex has the same benefits as its counterpart - it has lower production costs when compared with similar ferritic and austenitic grades and due to the materials increased tensile and yield strength, in many cases this gives the purchaser the welcomed option of purchasing smaller thicknesses without the need to compromise on quality and performance.

Benefits of UNS32750 Super Duplex Stainless Steel

Improved corrosion resistance in comparison to Duplex
Greater tensile and yield strength
Good ductility and toughness
Good stress corrosion cracking resistance (SSC)
Opportunity for purchases to reduce their material costs without compromising on quality

General Properties

Alloy 2507 is a super duplex stainless steel with 25% chromium, 4% molybdenum, and 7% nickel designed for demanding applications which require exceptional strength and corrosion resistance, such as chemical process, petrochemical, and seawater equipment. The steel has excellent resistance to chloride stress corrosion cracking, high thermal conductivity and a low coefficient of thermal expansion. The high chromium, molybdenum, and nitrogen levels provide excellent resistance to pitting, crevice, and general corrosion.

The impact strength is also high. Alloy 2507 is not recommended for applications which require long exposures to temperatures above 570⁰F because of the risk of a reduction in toughness.

Applications

Oil and gas industry equipment
Offshore platforms, heat exchangers, process and service water systems, fire-fighting systems, injection and ballast water systems
Chemical process industries, heat exchangers, vessels, and piping
Desalination plants, high pressure RO-plant and seawater piping
Mechanical and structural components, high strength, corrosion-resistant parts
Power industry FGD systems, utility and industrial scrubber systems, absorber towers, ducting, and piping

Standards

ASTM/ASME .......... A240 - UNS S32750
EURONORM............ 1.4410 - X2 Cr Ni MoN 25.7.4
AFNOR.................... Z3 CN 25.06 Az

Corrosion Resistance

General Corrosion
The high chromium and molybdenum content of 2507 makes it extremely resistant to uniform corrosion by organic acids like formic and acetic acid. 2507 also provides excellent resistance to inorganic acids, especially those containing chlorides.
In dilute sulfuric acid contaminated with chloride ions, 2507 has better corrosion resistance than 904L, which is a highly alloyed austenitic steel grade specially designed to resist pure sulfuric acid.

Stainless steel of type 316L (2.5%Mo) cannot be used in hydrochloric acid due to the risk of localized and uniform corrosion. However, 2507 can be used in dilute hydrochloric acid. Pitting need not be a risk in the zone below the borderline in this figure, but crevices must be avoided.

Isocorrosion curves, 0.1 mm/year, in sulfuric acid
with an addition of 2000 ppm chloride ions

Isocorrosion curves, 0.1 mm/year, in hydrochloric acid.
Broken line curve represents the boiling point

Critical Pitting Temperature (CPT) range for
various alloys in 1M NACl

Critical Crevice Corrosion Temperature (CCT)
for various alloys in 10% FeCl3

Intergranural Corrosion
2507's low carbon content greatly lowers the risk of carbide precipitation at the grain boundaries during heat treatment; therefore, the alloy is highly resistant to carbide-related intergranular corrosion.
Stress Corrosion Cracking
The duplex structure of 2507 provides excellent resistance to chloride stress corrosion cracking (SCC). Because of its higher alloy content, 2507 is superior to 2205 in corrosion resistance and strength. 2507 is especially useful in offshore oil and gas applications and in wells with either naturally high brine levels or where brine has been injected to enhance recovery.
Pitting Corrosion
Different testing methods can be used to establish the pitting resistance of steels in chloride-containing solutions. The data above were measured by an electrochemical technique based on ASTM G 61. The critical pitting temperatures (CPT) of several high-performance steels in a 1M sodium chloride solution were determined. The results illustrate the excellent resistance of 2507 to pitting corrosion. The normal data spread for each grade is indicated by the dark gray portion of the bar.

Crevice Corrosion
The presence of crevices, almost unavoidable in practical constructions and operations, makes stainless steels more susceptable to corrosion in chloride enviroments. 2507 is highly resistant to crevice corrosion. The critical crevice corrosion temperatures of 2507 and several other high-performance stainless steels are shown above.

Chemical Analysis

Typical values (Weight %)

C	Cr	Ni	Mo	N	Others
0.020	25	7	4.0	.27	S=0.001
PREN = [Cr%] + 3.3 [Mo%] + 16 [N%] ≥ 40

Mechanical Properties

Mechanical and Physical Properties
2507 combines high tensile and impact strength with a low coefficient of thermal expansion and high thermal conductivity. These properties are suitable for many structural and mechanical components. The low, ambient, and elevated temperature mechanical properties of 2507 sheet and plate are shown below. All of the test data shown are for samples in the annealed and quenched condition.
2507 is not recommended for applications which require long exposures to temperatures in excess of 570⁰F because of the increased risk of a reduction in toughness. The data listed here are typical for wrought products and should not be regarded as a maximum or minimum value unless specifically stated.

Mechanical Properties

Ultimate Tensile Strength, ksi	116 min.
0.2% Offset Yield Strength 0.2%, ksi	80 min.
0.1% Offset Yield Strength 0.2%, ksi	91 min.
Elongation in 2 inches, %	15 min.
Hardness Rockwell C	32 max.
Impact Energy, ft.-lbs.	74 min.

Low Temperature Impact Properties

Temperature ⁰F	RT	34	-4	-40
Ft.-lbs.	162	162	155	140
Temperature ⁰F	-76	-112	-148	-320
Ft.-lbs.	110	44	30	7

Elevated Temperature Tensile Properties

Temperature ⁰F	68	212	302	392	482
0.2% Offset Yield Strength, ksi	80	65	61	58	55
Ultimate Tensile Strength, ksi	116	101	98	95	94

Physical Properties

Density	lb/in3	0.28
Modulus of Elasticity	psi x 106	29
Coefficient of Thermal Expansion 68-212⁰F/⁰F	x10-6/⁰F	7.2
Thermal Conductivity	Btu/h ft ⁰F	8.7
Heat Capacity	Btu/lb/⁰F	0.12
Electrical Resistivity	W-in x 10-6	31.5

Processing

Hot forming
2507 should be hot worked between 1875⁰F and 2250⁰F. This should be followed by a solution anneal at 1925⁰F minimum and a rapid air or water quench.
Cold Forming
Most of the common stainless steel forming methods can be used for cold working 2507. The alloy has a higher yield strength and lower ductility than the austenitic steels so fabricators may find that higher forming forces, increased radius of bending, and increased allowance for springback are necessary. Deep drawing, stretch forming, and similar processes are more difficult to perform on 2507 than on an austenitic stainless steel. When forming requires more than 10% cold deformation, a solution anneal and quench are recommended.
Heat Treatment
2507 should be solution annealed and quenched after either hot or cold forming. Solution annealing should be done at a minimum of 1925⁰F. Annealing should be followed immediately by a rapid air or water quench. To obtain maximum corrosion resistance, heat treated products should be pickled and rinsed.

Welding

2507 possesses good weldability and can be joined to itself or other materials by shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), plasma arc welding (PAW), flux cored wire (FCW), or submerged arc welding (SAW). 2507/P100 filler metal is suggested when welding 2507 because it will produce the appropriate duplex weld structure.

Preheating of 2507 is not necessary except to prevent condensation on cold metal. The interpass weld temperature should not exceed 300⁰F or the weld integrity can be adversely affected. The root should be shielded with argon or 90% N2/10% H2 purging gas for maximum corrosion resistance. The latter provides better corrosion resistance.

If welding is to be done on only one surface and post-weld cleaning is not possible, GTAW is suggested for root passes. GTAW or PAW should not be done without a filler metal unless post-weld cleanup is possible. A heat input of 5-38 kJ/in. should be used for SMAW or GTAW. A heat input of about 50kJ/in. can be used for SAW.

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