Monel alloy for anti-corrosion forged valves

Monel alloy for anti-corrosion forged valves

For the same grade of Monel alloy, based on different technical standard systems, such as ASTM, SAE, AMS, MII, ANSI, ASME, QQ, or other current US technical standards for Monel alloys, not only the token of the grade is different but also the number and content of the specifications are not identical.

Monel alloy is a nickel-copper solid solution, in which copper is added as a non-oxidizing resist that enhances the corrosion resistance of the nickel alloy and strengthens it. And for better casting properties of the alloy, along with 1.5% - 3.5% ferrum, carbon is added, but only 0.15% can be dissolved in the alloy at normal temperature, and excess carbon will precipitate as a graphite phase. The addition of manganese and silicon improves the mechanical properties of the alloy, and in particular, the content of silicon has an important influence on the mechanical and physical properties of Monel alloy.

Monel alloys can be categorized into cast alloys and wrought alloys (rolled materials).
There are more than ten kinds of wrought Monel alloys in the United States, such as Monel 400, Monel 403, Monel 404, Monel R405, Monel 406, Monel 411, Monel K500, Monel 501, Monel 502, etc. And Monel has its own token in different US standard systems. For instance, in the UNS (Unified Numbering System), nickel alloys have five grades of wrought Monel alloys: solid solution strengthening types NO4404 (Monel 400), NO4404 (Monel 404) and NO4405 ( Monel R-405), and precipitation hardening types NO5500 (Monel K500) and NO5502 (Monel 502). Among them, the wrought Monel alloys used for the manufacture of corrosion-resistant forged steel valves are Monel 400 and Monel K500.

Monel alloys used for manufacturing refined  pumps, forged steel valves and accessories
The Class B Monel alloy with high silicon content (3.5% Si) is mainly used for the manufacture of shafts and abrasion resistant rings which are required to have good abrasion resistance because of the alloy's high strength and resistance to corrosion and wear. Class D (4.0% Si) Monel alloys are used to make parts that require even higher wear and corrosion resistance ability.

Integral and internal Monel alloy forged steel valves
Integral Monel alloy forged steel valves are valves whose shell and internal part are both Monel, which is mainly used for the regenerator of HF alkylation unit in refineries. Due to the high HF acid regeneration temperature (149 °C) and high water content, the integral Monel alloy forged steel valves are required, and they are also used in the production of ashless additives for refinery catalysts, and in high concentration chlor-alkali solution system and other working conditions.

Internal Monel alloy forged steel valves are valves whose shell is made of carbon steel or stainless steel, while the inner part is made of Monel alloy. The Monel alloy forged steel valve with carbon steel as the shell is mainly used in the low-temperature region of the HF acid system of the refinery alkylation unit since carbon steel has good corrosion resistance to low temperature (≤71 °C) anhydrous hydrofluoric acid. But carbon steel will form a film on the surface due to corrosion when it is used for a long time. And if it is used in the sealing part of the forged steel valve, the film formed after corrosion will affect the sealing performance of the forged steel valve.

The Cr13 type sealing material commonly used for carbon steel forged steel valves is not resistant to the HF acid corrosion, and Monel alloy as the inner part material can ensure the valve's sealing performance. Besides, the cost of using the internal forged steel valve is much lower than that of the integral type. Monel alloy forged steel valves with carbon steel as the shell can also be used in working conditions like seawater. 

The internal Monel alloy forged steel valves with stainless steel shell are used in ethylene, propylene, liquid oxygen, pure oxygen, seawater and other conditions. The integral and internal types used in the alkylation unit require a pressure class of CL300 for safety reasons. And for the internal type used in other working conditions, there are pressure class like CL150, CL300, or PN1.6 - 6.4MPa.