In today's knowledge sharing email let's learn a crucial skill that 90% of engineers struggle with.

Here’s the truth:
Even if you perfectly size the world’s best control valve,

Choosing the wrong material will make everything useless.

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The Good news,

Once you master material selection, you can use the same knowledge for

• Control valves.

• On-off valves.

• Pressure Relief valves.

• Field instrumentation devices.

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Why is material selection tricky?

Suppliers don’t always provide the exact material you request.

For example, You specified Alloy 800H.

But the vendor offered Alloy 800HT instead.

It seemed like a minor change, but 800HT posed a high risk of Stress Relaxation Cracking (SRC).

This leads to huge Rework and cost implications.

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But fortunately, if you know the basics,

Things become easier.

The Basics (Engineers Ignore):

Most valves use these material families:

• Carbon Steel
• Alloy Steels
• Stainless Steel
• Specialty Alloys (Hastelloy, Monel, etc.)

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Future Reference

Below is a bullet point summary,

But if you need a detailed PDF summary of Instrument material selection for future reference.

Then Reply to this email with "Engineers Guide to Material Selection PDF" And I will send it to you for your future reference.

PS: Last weeks guide "Engineers Guide to Level Sketch PDF" .
​Hope you have receive, If not let me know by replying to this email.

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4 Building Blocks

Four key elements determine material behavior:

Know the percentage of these 4 components and you can easily compare.

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​1. Carbon : Hardness​

For example:

• Carbon Steel is harder than Stainless Steel.
• SS316 (higher carbon) has higher pressure tolerance than SS316L (low-carbon variant).

Hence you see as per ASME B16.5 Standard,

Carbon steel can handle more pressure & temperature than Stainless Steel.

But also note we can't just keep adding carbon.

If the carbon goes beyond 2.1% then material become more brittle.

Also another disadvantage is that it is very prone to corrosion.

So, if you expect corrosion then look for another component.

And that is .....

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​2. Chromium: Corrosion Resistance:​

Now note that Chromium needs to be in a substantial amount for it to make a difference.

Chromium must be ≥11% to effectively improve corrosion resistance.

Common Question:

You have pipe material mentioned as 13% Chromium.

Your Valve vendor has two choices.

• Carbon Steel.

• Stainless Steel.

Which material would choose.

Carbon steel has lower chromium content so you can't accept.

SS316 has higher chromium content so you can accept.

FYI: SS316 has around 18% Chromium.

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​3. Molybdenum: Special Corrosive Environments​

Now if you have Acids like

• Sulfuric Acid

• Phosphoric Acid.

• Hydrochloric Acid.

Molybdenum adds protection against pitting and crevice corrosion.

​4. Nickel : High Temperature​

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Nickel enhances performance in elevated temperatures.

For example, SS316 tolerates higher temperatures (~800°C) than SS316L due to higher nickel.

So, for high temperature applications look for nickel content.

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Summary :

This was a very bird's eye view of the material selection process.

It's not very straightforward.

But as an engineer,

You need to have the basic understanding of materials and be able to distinguish if you notice any alarming issue.

It's not humanly possible to cover entire material selection in one email.

But I Hope,

I was able to serve you and give you a taste to explore material selection in depth.

In case you want to learn this in depth, ACV (Advance Control Valve Cohort) starts soon, waitlist is open. Join here​

PS : Here is webinar I had conducted on Control Valves that explains this concept of material selection.​

Regards,

You Control Valve Geek,

Principal Engineer

Asad