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Material Selection for Metal-to-Metal Seal

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Hush

Hush

Mechanical
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I'm hoping someone can steer me in the right direction for material selection of a malleable metal-to-metal seal.

I want it to be fairly soft approx. preferably in the 50 HRB neighbourhood but 80 HRB max.

I'm sealing against AISI 4130.

Retained fluid is sour gas expected to contain about 25% CO2, 20% H2S, some water, some chlorides @ around 200 F.

My first thought was 625 but its expensive and I'm not sure I can get it soft enough. I'm leaning toward 316 annealed but would prefer something softer. I'm also wondering if a copper alloy might work in this environment
 
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Copper and copper alloys have excellent resistance to hydrogen sulfide in dry conditions. In the presence of moisture, corrosion is markedly increased. You may consider some copper-nickel alloys, which would offer the best resistance:

C71000 79 Cu & 21 Ni
C71300 75 Cu & 25 Ni
C71500 70 Cu & 30 Ni

These alloys should have hardnesses in the range of 36-45 HRB in the annealed condition.

You may also consider titanium. Commercially pure Ti has a hardness around 70 HRB, as do some of the other lightly alloyed grades (corrosion grades containing Ru, Pd, etc.). They would have good resistance to H2S in anything other than very high concentrations and pressures.
 
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Thanks TVP,

I forgot to mention 15,000 psi cwp. I guess that rules out the titanium blends.
 
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I think that the copper-nickel alloys are probably not going to be very suitable either, but offered that they may be an option.

I just checked a reference guide from Special Metals, and you should probably investigate Nickel 200 (UNS02200). It is generally resistant to these conditions, but stress-corrosion cracking can occur in polythionic acids at or near ambient temps. Polythionic acids are often produced by partial oxidation of wet H2S when exposed to air. The presence of Cl- may exacerbate the SCC effect.
 
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TVP,

Your suggestions have steered me to Monel 400 annealed (N04400). Pricey (about 7 USD/lb) but it meets most of the requirements.

Thanks very much for your help.
 
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Your most welcome, Hush.
 
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You can applied a metal coating to the seal areas. Thermal Spray applied coatings. Which are used in the air and landbase turbines industries, chemical and refinerys. Plus some of the nickel base alloy are fused coatings which applied over 4140 and other heat treated materials are over 80,000 psi. Visit and look and the materials page.

Ken Norris
 
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