Incoloy 926 Introduction

Solid Solution
Strengthened Alloy

Nickel

Iron

Chromium

Molybdenum

Copper

Nitrogen

Corrosion
Resistance

73

Mechanical
Behavior

69

Purity

80

Overview

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INCOLOY® alloy 926 (UNS N08926 / W. Nr. 1.4529 / INCOLOY® alloy 25-6MO) is a super-austenitic stainless steel containing 6% molybdenum and enhanced by an addition of nitrogen. The nickel and chromium contents of this alloy make it resistant to a wide range of corrosive environments. The alloy is especially resistant to non-oxidizing acids such as sulfuric and phosphoric. The high molybdenum content and nitrogen provide resistance to pitting and crevice corrosion, while copper enhances resistance to sulfuric acid.

INCOLOY alloy 926 is a fully austenitic alloy containing 6% molybdenum and offering excellent corrosion resistance in a wide variety of aggressive, aqueous environments. It replaces the conventional, austenitic stainless steels (AISI 316 and 317), where their capabilities are pushed to their performance limits. The alloy, therefore, falls into a “super austenitic stainless steel” category. It can also represent a cost-effective alternative to the higher nickel alloys in some marine and chemical processing environments.

One of the outstanding attributes of INCOLOY alloy 926 is its resistance to environments containing chlorides or other halides. This alloy is especially suited to handle high-chloride environments such as brackish water, sea water, caustic chlorides and pulp mill bleach systems. Applications include chemical and food processing, pulp and paper bleaching plants, marine and offshore platform equipment, salt plant evaporators, air pollution control systems, and condenser tubing, service water piping, and feedwater heaters for the power industry.

Mechanical Properties

INCOLOY alloy 926 shows higher mechanical properties than those for the austenitic stainless steels, such as AISI 316L. The alloy has higher design values than lower strength materials such as 316L, enabling the use of thinner sections.

Corrosion Resistance

INCOLOY alloy 926 is a fully austenitic alloy offering excellent resistance to pitting and crevice corrosion. Performance in these areas is often measured using Critical Pitting Temperatures (CPT), Critical Crevice Temperatures (CCT), and Pitting Resistance Equivalent Numbers (PREN). The corrosion resistance of stainless steel is, basically, dependent on their chemical compositions.

As a general rule, the higher the PREN, the better the resistance to pitting. However, alloys having similar values may differ considerably in actual service. Those with values greater than 38 on the PREN scale offer more corrosion resistance than the austenitic stainless steels. INCOLOY alloy 926, with its PREN of 47, offers a cost-effective means of avoiding aggressive chloride attack.

The Critical Pitting Temperature (CPT) test involves exposing samples to 6% ferric chloride solutions (ASTM Standard G48) and raising the temperature by incremental amounts until the onset of pitting. New, unexposed test specimens and fresh 6% FeCl3 solution are used at each test temperature. The minimum accepted temperature for North Sea offshore applications is 40°C (104°F), while in pulp and paper bleaching environments, this temperature would typically be 50°C (122°F). The critical pitting temperature for INCOLOY alloy 926 has been shown to be 65-70°C (149-158°F).

Physical Properties

Mechanical Properties