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π My Control Valve Trim Hardness Special Guide
Published 4 months agoΒ β’Β 3 min read
The 3 Things You will learn today are as follows.
The Hardness Selection guide in Valve Trims.
The Trim Table in API standard.
The "Pill" that makes us world class engineers.
Today's knowledge sharing article is a special one.
I have not shared this kind of depth with anyone.
But you are special.
You chose to read it,
So, here's the part very few engineers know about control valve trim hardness selection.
#1 - Engineering Learning
Control valves face
High Pressure.
High Velocity.
This cuts through soft metal.
Standard Stainless Steel cannot survive alone.
So we harden the trim.
Why harden the Trim?
Think of a diamond-tipped drill.
That we use for Super-hard surface.
The perfect combination.
The core is steel.
The tip is diamond (hard).
We do the same for valves.
We weld "Armor" onto soft 316SS.
This protects the critical sealing zones.
But how do you measure how strong is this "Armor"
To be an Expert, Know the Units
You cannot manage what you cannot measure.
In the valve world, we use HB.
HB = Brinell Hardness.
The higher the number, the harder the armor.
If you don't know the typical values,
You cannot be confident engineer.
What are the Typical Values?
Memorize these three benchmarks:
1.Material Name: 316 Stainless Steel (Soft)
Hardness Value β ~150 to 190 HB.
Note: This is your standard body material.
2.Material Name: 17-4 PH Stainless Steel (Stem).
Hardness Value β ~275 to 350 HB.
3.Material Name: Stellite 6 (The Armor)
Hardness Value β ~350 to 450 HB.
Note: The API Standard requires Min 350 HB.
Why do these specific numbers matter?
The "50 HB" Golden Rule
Soft metals hate sliding against each other.
Microscopically, they stick and tear.
We call this Galling (Cold Welding).
The 50 HB Engineering Rule
Moving parts must have different hardness.
Ideally, 50 HB difference or more.
Example: If your Plug is 316SS (160 HB).
And your Seat is 316SS (160 HB).
They will destroy each other.
Now the next question is that
Whether you harden entire trim ?
Or only some parts ?
Full vs. Half Hardfacing
You choose based on the application.
The industry uses two main terms:
1. Half Stellite
β Only the Seat Ring is armored.
β The Plug remains soft (Standard).
Example : API Trim 12
2. Full Stellite (Trim 16)
β Both Seat and Plug are armored.
β Use this for severe service.
Example : API Trim 16.
But how do you spot this on an API trim chart?
The API Table "Secret Code"
Take API 600 or API 623 Standard.
Open the Trim Number Chart.
Look at the "Nominal Trim" column.
The secret lies in one small word: "AND".
Refer below picture.
The Hack:
If you see "AND" (e.g. Trim 12 or Trim 8):
"18Cr-8Ni-Mo AND Trim 5"
β Two materials listed means Half Stellite.
Refer below picture (Or right click on picture to load it)
Table with "AND"
If you see NO "AND" (e.g., Trim 16 or Trim 5):
"Co-Cr A"
β One material listed means Full Stellite.
Refer below picture of table values without "AND"
Table without "AND" values
Summary: Which one to pick?
Don't guess.
Use this simple thumb rule:
General Service: Trim 12 (Half Stellite).
High Pressure Drop: Trim 16 (Full Stellite).
Steam/Thermal Shock: Stellite 21. (Mostly used in Aviation Industry)
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