GENERAL PROPERTIES:-

Duplex 2507 (UNS S32750) 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.

APPLICATION:-

• 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

COROSSION RESISTANCE:

GENERAL COROSSION:-

• high chromium and molybdenum content of 2507 makes it extremely resistant to uniform corrosion by organic acids like formic and acetic acid.
• provides excellent resistance to inorganic acids, especially those containing chlorides.
•  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.

INTERGRANURAL COROSSION:-

• Low carbon content greatly lowers the risk of carbide precipitation at the grain boundaries during heat treatment.
• Is highly resistant to carbide-related intergranular corrosion.

STRESS COROSSION CRACKING:-

• Duplex structure of 2507 provides excellent resistance to chloride stress corrosion cracking (SCC).
• 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 COROSSION:-

• Different testing methods can be used to establish the pitting resistance of steels in chloride-containing solutions.

CREVICE COROSSION:-

• Highly resistant to crevice corrosion.

PROCESSING

HOT FORMING:-

2507 should be hot worked between 1875°F and 2250°F. This should be followed by a solution anneal at 1925°F 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 1925°F. 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 300°F 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.