Maunfacture Inconel Alloy 725 UNS N07725 ASTM B805 tube sheet ring

Overview

INCONEL alloy 725 (UNS N07725) is a nickelchromium-molybdenum-niobium alloy that is highly resistant to corrosion and is age hardenable for extremely high strength. It has essentially the same corrosion resistance as INCONEL alloy 625, which is widely used in a broad range of severely corrosive environments.

The strength of age-hardened INCONEL alloy 725 is of the order of twice that of annealed alloy 625. Because the strength of alloy 725 is developed by heat treatment, not by cold work, ductility and toughness remain high.

Also, strength can be imparted to large or non-uniform sections that cannot be strengthened by cold work.

High levels of nickel and chromium provide corrosion resistance in reducing and oxidizing environments. The substantial molybdenum content enhances resistance to reducing media and provides a high degree of resistance to pitting and crevice corrosion. Additionally, the combination of elements makes the alloy resistant to hydrogen embrittlement and stresscorrosion cracking.

Limiting Chemical Composition, %

Nickel...................................................................................................................................................................................55.00-59.00

Chromium..............................................................................................................................................................................19.00-22.5

Molybdenum............................................................................................................................................................................7.00-9.50

Niobium....................................................................................................................................................................................2.75-4.00

Titanium...................................................................................................................................................................................1.00-1.70

Aluminum.................................................................................................................................................................................0.35 max.

Carbon......................................................................................................................................................................................0.03 max.

Manganese...............................................................................................................................................................................0.35 max.

Silicon.......................................................................................................................................................................................0.20 max.

Phosphorus............................................................................................................................................................................0.015 max.

Sulfur.......................................................................................................................................................................................0.010 max.

Iron..............................................................................................................................................................................................Balance*

*Reference to the ‘balance’ of a composition does not guarantee this is exclusively of the element mentioned but that it predominates and others are present only in minimal quantities.

Physical Constants

Mechanical properties

The strength of nconel Alloy 725 is mainly due to its nickel and chromium content. These two elements form a strengthening phase in the alloy, which increases the tensile strength and yield strength of the alloy. In addition, the addition of aluminum and titanium further enhances the strength and toughness of the alloy. As a result, Inconel Alloy 725 has excellent tensile properties and yield strength to withstand high loads and high-temperature environments. The strength of nconel Alloy 725 is mainly due to its nickel and chromium content. These two elements form a strengthening phase in the alloy, which increases the tensile strength and yield strength of the alloy. In addition, the addition of aluminum and titanium further enhances the strength and toughness of the alloy. As a result, Inconel Alloy 725 has excellent tensile properties and yield strength to withstand high loads and high-temperature environments.

Corrosion Resistance

High nickel, chromium and molybdenum contents enable INCONEL alloy 725 to resist a broad range of corrosive environments. The alloy is especially resistant to media containing carbon dioxide, chlorides and hydrogen sulfide, such as those encountered in deep sour gas wells. In such environments, INCONEL alloy 725 resists corrosion, pitting, hydrogen embrittlement and stress-corrosion cracking.

INCONEL alloy 725 is approved under NACE MR0175 for use in sour gas wells.

INCONEL alloy 725 displays excellent resistance to general and localized corrosion in brines and sea water.

Heat Treating

INCONEL alloy 725 is strengthened by precipitation of gamma double-prime (γ ”) phase during an aging heat treatment.

Before it is aged, the material should be given a solution anneal at 1900°F (1040°C). Air cooling after solution annealing is the preferred cooling method.

For sour gas applications, the recommended aging treatment is 1350°F (730°C)/8h/furnace cool at 100°F (56°C)/h to 1150°F (620°C)/8h/air cool.