What is Your Instrument Made Of?

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What is Your Instrument Made Of? Visaya Weekly episode 34

Hello guys Germán here from Visaya

Now at this very moment, there is an instrumentation engineer selecting and dimensioning some instruments.

She, yes she #feminism has to select the appropriate process connection, dimensions, ranges, certifications etc.

But there is one feature that has puzzled Instrumentation engineers for years:

The material.

Selecting the right material and coatings will guarantee that your instruments will withstand the process conditions and it will not contaminate your products.

So where do we start from? How does a instrumentation engineer select the right material? What are those numbers and what do they mean?

Ok so let’s start from the basics.

Materials used in the industry are divided among 4 families

  • Plastics
  • Ceramics
  • Metals
  • Composites

Most of the instruments used in process automation are made from metallic materials and the most common metal used in instruments is stainless steel.

So what’s stainless steel?

To explain this, I need to explain what steel is!

Steel is made from one of the most common metals in the world iron [Fe]

Iron on its own, would not have been able to change the world as steel did. Actually, you can measure the economic growth of a country by measuring how much steel it produces and consumes

To make steel you need to add carbon to iron, steel has a carbon content between 0.08% and 2 percent,

This little content of carbon is able to increase the mechanical properties of iron making one of the most versatile materials ever used.

If you remember the temperature video from some weeks ago.

What does a Instrumentation engineer have to do with a Katana?

I explained how Japanese sword makers were able to tell temperature by looking at the colour of the glowing katana,

Actually, they did much more, They had a deep understanding of the properties of the metal and the effects of carbon content in the blade.

The core of the blade or shingane was made with low carbon steel that is resilient and flexible; the edge, on the other hand, was done with tamahagane a high content carbon iron that is strong and resistant perfect for the edge of one of the deadliest of weapons.

But just like iron, steel has an enemy,  oxygen [O2]. Oxygen reacts quite easily with iron and corrodes its surface, that is why iron is commonly found with a reddish color.

By adding at least 12% of Chrome and some Nickel to the steel alloy it becomes Stainless.

This occurs because the chrome creates a passivating layer on the surface of the steel avoiding that iron reacts with oxygen, and it doesn’t rust so is inert and keeps its silver color.

The Austenitic Stainless Steels are the most common in the industry.

If you look closely to your silver ware it says 18/10 stainless steel.
This means that has 18% Chrome and 10% Nickel.

As a instrumentation engineer, this is known as AISI 304 if you add some Molybdenum you get AISI 316 that is the most commonly used stainless steels for its local corrosion resistance and its perfect for food and life science applications.  

And from here is just some cooking or alchemy.

Add some titanium [Ti]  (AISI 321) or tantalum [Ta] (AISI 347) and you avoid intergranular corrosion.

Add some more Chrome and Nickel  (AISI 310) and you increase the stability at high temperatures.

Keep going and we stop calling them steel and they become Nickel based Alloys

Like Alloy 600, Hastelloy or C276 with high oxidation and corrosion resistance even at high temperatures.

The price of these alloys varies depending on availability and the type of alloying elements.

And buying the most expensive alloy will not guaranty that is the best fit for your application.

What I can really recommend to any instrumentation engineer is that you buy your instruments from companies that deliver the 3.1 certificate with all the information from the heat and that the check the used mills have properly tested the properties and chemistry of the alloys.

Additionally, you should perform PMI or Positive material identification tests on your plant to make sure that you are installing the right material.

Selecting the right material is not easy but your instrumentation and equipment suppliers can help you with that.

If you have any application questions leave them in the comment section below or send me an email

I will be happy to address you to the right answer.

Thank you for watching

Till next time

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