Overview
Monel belongs to Ni-Cu family of nickel-based corrosion-resistant alloy. With composition of 70% Ni and 30% Cu, Monel has the widest application among all nickel-based corrosion-resistant alloys. It was first developed by International Nickel Co., Ltd.
Monel alloy features high strength and toughness, as well as excellent resistance to reducing acid, strong alkali medium and seawater. Therefore, it is commonly used for the equipment of hydrofluoric acid (HF), brine, neutral medium, alkali salt, and reducing acid media.
Introduction of Forged Monel
Monel alloys are available in both forged alloy and deformed alloy (rolled material). In terms of forged Monel alloy, ASTM A494 standard lists five grades, i.e., M35-1, M35-2, M-30H, M-25S and M-30C as Table 1; There are also five cast Monel alloys in the US Federal Standard QQ-N-288 as Table 2.
| Grades | C | Mn | Si | P, S | Cu | Fe | Ni | Nb |
|---|---|---|---|---|---|---|---|---|
| M35-1 | ≤0.35 | ≤1.5 | ≤1.25 | ≤0.03 | 26-33 | ≤3.5 | Remainder | / |
| M35-2 | ≤0.35 | ≤1.5 | ≤2 | ≤0.03 | 26-33 | ≤3.5 | Remainder | / |
| M-30H | ≤0.3 | ≤1.5 | 2.7-3.7 | ≤0.03 | 27-33 | ≤3.5 | Remainder | / |
| M-25S | ≤0.25 | ≤1.5 | 3.5-4.5 | ≤0.03 | 27-33 | ≤3.5 | Remainder | / |
| M-30C | ≤0.3 | ≤1.5 | ≤1-2 | ≤0.03 | 26-33 | ≤3.5 | Remainder | 1-3 |
| Grades | C | Si | Mn | Cu | Fe | Ni | Nb+Ta |
|---|---|---|---|---|---|---|---|
| Class A | ≤0.35 | ≤2 | ≤1.5 | 26-33 | ≤2.5 | 62-68 | / |
| Class B | ≤0.3 | 2.7-3.7 | ≤1.5 | 27-33 | ≤2.5 | 61-68 | / |
| Class C | ≤0.2 | 3.3-4.3 | ≤1.5 | 27-31 | ≤2.5 | ≥60 | / |
| Class D | ≤0.25 | 3.5-4.5 | ≤1.5 | 27-31 | ≤2.5 | ≥60 | / |
| Class E | ≤0.3 | 1-2 | ≤1.5 | 26-33 | ≤2.5 | ≥60 | 1-3 |
Selection of Monel Alloys for Corrosion Resistant Valves
M35-1, M35-2, and Classes A and E in QQ-N-288 are commonly used to make refined Monel alloy pumps, valves, and accessories. Class B Monel alloys featuring high Si (3.5 %Si) are mainly used to manufacture shafts and wear rings that require good wear resistance due to their high strength and resistance to corrosion and wear. Class D Monel alloys containing 4.0 % Si are used to make parts that require higher wear resistance and corrosion resistance.
Introduction of Monel Corrosion Resistant valve
Monel alloy valves are available in pure Monel valve and Monel trim valve. The pure Monel valve means that the valve housing and body are all made in Monel, mainly used in the HF acid regeneration tower section of the refinery alkylation unit. Due to the high regeneration temperature (149 °C) and high water content of HF acid, the overall valve, including housing and the body, should be made in Monel, known as integral Monel alloy valve. In addition, the integral Monel alloy valve is also used in the production of ashless additives for refinery catalysts and high concentration chlor-alkali systems and the like in chlor-alkali plants.
The Monel trim valve means that the valve housing is made of carbon steel or stainless steel while the valve body is made of Monel alloy. The carbon steel-housed Monel valve is mainly used in the low temperature region of the HF acid system of the refinery alkylation unit, as carbon steel exhibits relatively good corrosion resistance to low temperature (≤71 °C) anhydrous hydrofluoric acid (HF). However, a long-term exposure to such environment will lead to corrosion which can cause the carbon steel to form a film on the surface. If carbon steel is used in the valve sealing part, the film formed after corrosion will affect the sealing performance of the valve. Kindly note that type Cr13 sealing material commonly used in carbon steel valves is insufficient to resist the corrosion of HF acid, while Monel alloy used for the valve body, can guarantee the sealing performance. Besides, the cost of using Monel alloy for the internal part of the valve is way cheaper than that for the whole valve. Monel-trimmed valves with carbon steel as the housing can also be used in harsh working conditions such as seawater.
The Monel trim valve with the housing made of stainless steel, is used in ethylene, propylene, liquid oxygen, pure oxygen, seawater and other conditions. The Monel alloy valve and Monel-trim valve used in the alkylation units require a pressure level of CL300 lb for safety consideration, while Monel-trimmed valves purposed on other operating conditions require safety pressure level of CL150 and CL300 lb, or PN116 ~ 614MPa.
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