Bolting Procedures That Don’t Betray You at Startup
- 14 minutes ago
- 3 min read
Bolting Procedures
Bolting Procedures That Don’t Betray You at Startup
Everybody thinks bolting is “tighten it until it feels right.”
That mindset is how flanges leak, couplings walk, and “minor maintenance” turns into a shutdown.
A bolting procedure is a repeatable recipe that gets consistent clamp load without guessing.
And yes, it matters way more than a torque number sitting on a drawing.
What a Bolting Procedure Actually IS
A bolting procedure is a written, repeatable method that controls the variables that change clamp load:
- Joint condition
- Fastener condition
- Lubrication
- Tightening pattern
- Tightening method
- Verification method
If you don’t control those, your results are basically random.
Step 1: Identify the Joint Before You Touch a Tool
Before anyone grabs a wrench, confirm:
- Joint type (flange, coupling, structural, turbine, heavy equipment, etc.)
- Fastener details (size, grade, thread pitch, washer style, nut type)
- Condition (rust, galling, damaged threads, paint, grit, old gasket material)
- Lubrication status (dry, lubed, coated, anti-seize, or unknown)
If you don’t know what lube is on the threads, your torque value is just a guess with confidence.
Step 2: Choose the Tightening Method
Pick the method based on risk and repeatability.
Torque only:
Fast and common, but sensitive to friction changes.
Use when the joint is forgiving and lubrication is controlled.
Torque plus angle:
More repeatable than torque-only.
Great when you need better consistency but still want torque tools.
Tensioning:
Best for critical joints, big flanges, or when torque scatter becomes a problem.
Targets bolt stretch more directly than torque.
Direct tension measurement:
Ultrasonic or extensometer methods.
This is precision territory and it’s the move when the joint is high consequence.
Step 3: Prep the Joint (This Is Where Wins Come From)
This is the part people skip and then blame the tool.
Do the basics:
- Clean threads (wire brush if needed)
- Chase threads if they’re damaged
- Replace stretched or questionable bolts
- Confirm correct washers and proper seating
- Verify gasket condition and alignment
- Clean joint faces and remove old gasket debris
Step 4: Build the Tightening Sequence
Most flanges use a star (cross) pattern to distribute load evenly.
For flanges:
- Use a cross pattern
- Use multiple passes
- Re-check after a short rest if procedure requires it
For structural joints:
- Follow the engineered sequence if provided
- If none exists, tighten in a pattern that draws the joint together evenly and avoids side-loading
The goal is even clamp. Not “get it done fast.”
Step 5: Use Staged Passes
A solid procedure usually looks like this:
- Pass 1: snug everything to seat the joint
- Pass 2: 30% of final value
- Pass 3: 60% of final value
- Pass 4: 100% of final value
- Verification pass: check again at final value
This reduces uneven gasket crush, avoids warped joints, and cuts rework.
Step 6: Control Torque Scatter (The Silent Joint Killer)
Torque scatter is why two bolts at the same torque can have totally different clamp loads.
The biggest causes:
- Inconsistent lubrication
- Dirty or damaged threads
- Different washer types or surface finishes
- Worn sockets or poor tool alignment
- Bad reaction setup that causes side-loading
- Rushing the tightening cycle with no control
You don’t fix torque scatter by yelling at techs.
You fix it by standardizing inputs.
Step 7: Tool Setup Matters More Than People Admit
If you’re using powered torque tools:
- Confirm the tool is in calibration
- Use the correct socket and reaction setup
- Keep the tool square to the fastener
- Avoid “walking” the socket on/off under load
- Don’t run the tool at the extreme top of its range if avoidable
A torque tool out of calibration is a confident liar.
Step 8: Document It So Nobody Freestyles It Later
A real bolting procedure should include:
- Joint description and location
- Fastener spec and quantity
- Lubrication requirement (include exact product if possible)
- Pattern diagram or numbered sequence
- Pass schedule (snug, 30%, 60%, 100%, verify)
- Final torque / angle / tension values
- Tooling required
- Verification method
- Acceptance criteria
If it isn’t written down, it isn’t a procedure.
Step 9: Verification Isn’t Optional for Critical Joints
Depending on the job, verification may include:
- Final torque verification pass
- Breakaway checks (where appropriate)
- Paint mark witness lines for visual confirmation
- Angle verification
- Tension verification if tensioning was used
- Leak check and re-torque plan if required
Startup will audit your work. Usually at the worst possible time.
Bolting procedures aren’t red tape.
They’re how you prevent downtime, rework, and those “why is it leaking again” meetings.
If you want the joint to survive thermal cycles, vibration, and real life,
you need a procedure that controls the variables, not just a torque number.
Comments