π " Three Times Better (Engineer) "
The 3 Things You will learn are as follows.
β’ The 14 Timeless Rules in "Level Sketch".
β’ The best Standard for Level Instrumentation.
β’ Get your shoes "Dirty".
#1 -Engineering Question
Hello Anti-Copy Paste Engineer,
I have made and checked more than 10,000+ Level Sketches in my career and today's article is a summary of my entire experience.
Below is a bullet point summary, but if you need a detailed PDF summary of Level Sketch for future reference.
Then Reply to this email with "Engineers Guide to Level Sketches PDF" And I will send it to you for your future reference.
During my career, I had heard engineers say.
This document is useless.
Why does this document exists.
I believe this is the MOST IMPORTANT Engineering Document.
Let answer that before you learn the golden rules.
Why need Level Sketch
Instrumentation is complex.
And Piping, Process Mechanical engineering discipline must be aligned with instrumentation.
So "Level Sketches were born".
There are 3 reasons why your instrumentation installation fails on site.
- Wrong Connections (Flanges don't match).
- Impossible Maintenance (You can't remove it).
- Bad Elevations (The range doesn't work).
All this gets solved
If you correctly design level sketches.
Here is my Level Sketch Complete Guide.
Use this checklist before you issue for construction.
Rule 1: The Material-Rating Check
The Rule: Check the Flange Rating as per ASME B16.5.β
Why follow it: Instrumentation is usually Stainless Steel (SS).
The Vessel is usually Carbon Steel (CS). These materials have different Pressure-Temperature ratings.
SS might require a higher flange rating than CS at high temperatures.
The Risk: A common site disaster. The vessel nozzle is 600#. The instrument spec requires 900# to handle the same pressure. Now they will not bolt together.
How to fix: Check the PT rating of both materials at design Pressure & temperature. here's the guideβ
Rule 2: The "Min 300#" Clause
The Rule: Check if the project has a "Minimum 300# Flange" clause.
Why follow it: Many Oil & Gas clients mandate this. It provides mechanical robustness. It helps with vibration resistance.
The Risk: You buy 150# flanges because the pressure is low. The client rejects them during inspection. You have to scrap the entire lot.
How to fix: Search your "General Instrument Specification" for the keyword "300#" or "Min 300#".
Rule 3: Standardize Connection Sizes
The Rule: Use the correct industry-standard sizes.
Why follow it: Certain technologies need specific sizing. This ensures signal strength and mechanical fit.
The Risk: Poor signal quality. Physical mounting issues.
How to fix: Here's quick guide on common flange sizes.
- 2" for Side Mounted GWR chambers.
- 2" for Magnetic Level Gauges (MLG).
- 3" for Diaphragm Seals (Better sensitivity).
- 4" for Top Mounted Non-Contact Radar.
Rule 4: The Mag Gauge Overlap
The Rule: If the range is long, overlap the gauges.
Why follow it: Every Mag Level Gauge has a "dead zone". This occurs at the top and bottom of the float chamber.
The Risk: If you mount them tip-to-tail. You will have a blind spot of 200mm. The operator cannot see the level there.
How to fix: Ensure the visible indication overlaps between the two gauges.
Rule 5: Maximum Transport Length
The Rule: Limit the single-piece length of Mag Level Gauges.
Why follow it: Shipping and handling limits. A 6-meter long instrument is a nightmare to transport.
The Risk: The instrument arrives bent.
Or it does not fit in the shipping container.
How to fix: Limit single sections to ~5000mm. Split anything longer into segmented sections.
Rule 6: The Standpipe Sizing
The Rule: Use a 4" Standpipe (Highly Recommended). Avoid 2" pipes.
Why follow it: A 2" pipe has very low holding power.
If you weld a 3" nozzle onto a 2" pipe, it is weak. Also, 2" pipes restrict flow during flushing.
The Risk: Vibration can crack the welds. The measurement becomes sluggish.
How to fix: Standardize on 3" or 4" Standpipes. Use Schedule 80 for robustness.
Rule 7: SIL Instrument Separation
The Rule: SIL instruments must have separate tapping points. They cannot be clubbed on one standpipe.
Why follow it: To avoid Common Cause Failure (CCF). If one standpipe clogs, you lose everything.
The Risk: Imagine a 2oo3 voting system on one standpipe. If that standpipe blocks. Your safety system is blind. The plant is unprotected.
How to fix: Give critical SIL instruments their own dedicated nozzles.
Rule 8: The "Headroom" Check
The Rule: Verify removal space in the 3D Model.
Why follow it: Guided Wave Radars have rigid probes. They often need to be pulled straight up.
The Risk: You install the Radar. But there is a steel beam 500mm above it. You can never remove the sensor for maintenance.
How to fix: Model the "withdrawal envelope" in the 3D review.
Rule 9: The 10-90% Range Rule
The Rule: Keep LL and HH alarms between 10% and 90% of the span.
Why follow it: Instruments are least accurate at the limits. These are the "dead zones".
The Risk: If you set the HH alarm at 98%. The instrument might saturate before triggering the alarm.
How to fix: Ensure all critical setpoints are inside the operating range.
Rule 10: Isolation Philosophy
The Rule: Define Single vs. Double Block & Bleed (DBB).
Why follow it: High-pressure services require double isolation. This ensures operator safety during maintenance.
The Risk: Using a single valve on a 600# Hydrocarbon line. This puts the maintenance technician at risk of a leak.
How to fix: Check the "Piping Material Specification" (PMS).
Rule 11: The DP Calculation Box
The Rule: Show the basic DP calculation on the sketch.
Why follow it: It clarifies the calibration range instantly. The installation team needs this.
How to fix: Use this formula: DP (Inches H2O) = S.G. * Height (Inches)
Specify if it is:
- Wet Leg.
- Dry Leg.
- Capillary.
Rule 12: The Battery Limit
The Rule: Clearly mark the "Scope Line".
Where Piping ends and Instrumentation begins.
Why follow it: To avoid "Scope Gaps".
Especially for flushing rings and gaskets.
The Risk:
- Who supplies the bolts?
- Who supplies the ring?
- Both vendors assume the other is doing it. Result: Missing parts on site.
How to fix: Draw a dotted line labeled "Battery Limit".
Rule 13: Thermowell Isolation
The Rule: Never put an isolation valve on a Thermowell.
Why follow it: The Thermowell is the pressure boundary. The sensor can be removed safely.
The Risk: Adding a valve adds cost. It adds leak points.
Also ensure there is enough space for thermowell insertion and removal. (Especially multipoint assembly).
Rule 14: Slug Service in Vessel.
The Rule: Use slanted (45-degree) nozzles for slurries.
Why follow it: In heavy viscous service. Horizontal nozzles accumulate solids.
The Risk: The nozzle blocks. The measurement fails.
How to fix: Angle the nozzle down. Gravity will drain the solids back into the vessel.
#2- Engineering Standard
A World Class Engineer
Always knows the Standards.
Here are one the best standards on the planet for Level Instruments study.
1. API RP 551 (Process Measurement) This is the "Top Reference standard" for installation. It defines why we use standpipes. It defines where to put isolation valves.
2. PIP PCCEL001 The industry gold standard. Use this for detailed installation drawings.
3. ASME B16.5 The law for Pressure-Temperature ratings. Here's the guide on how you can calculate the Flange ratings.
#3 -Career Tip
The Fastest Way to Learn
Stop trying to learn everything alone.
You do not have enough time.
To make every mistake yourself.
Most young engineers are afraid to ask questions.
They think it makes them look stupid.
The Reality
Senior engineers are waiting to teach you.
They have 20 years of mistakes in their head.
They want to pass that knowledge on.
But they will not chase you.
You have to show interest.
The "Open Door" Secret
If you walk in with a genuine question.
They will talk for hours.
They don't just want to help.
They love to help.
Here is your action plan:
- Find the most experienced engineer in your office.
- Don't ask: "How do I do this?" (That is lazy).
- Ask: "Why did we choose this design over that one?"
- Ask: "What was the biggest problem you faced on your last project?"
You can learn in 10 minutes.
What took them 10 years to figure out.
Don't learn the hard way.
Just ask.
Your Feedback (Means a lot)
Your feedback means a lot (To make this articles better).
- Found Super Valuable - Reply "1".
- Found Decently Valuable - Reply "2".
- Can be improved - Reply "3".
Want a PDF guide on Level Sketches.
Reply to this email with "Engineers Guide to Level Sketches PDF" And I will send it to you for your future reference.
Until next Monday,
Happy Learning and Keep Smiling.
Asad Shaikh
Your Well Wisher and Instrumentation Friend!! π
See you next week!
PS : The Wait-list for ACV 2026 is getting all excited with 600+ Engineers, If you plan to master Control Valves (Including Sizing) in 2026, Then Click here to join the list.β
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