Bolted-Joint Torque Sequence Work Instruction Example

What a torque sequence does

Torque is a stand-in for what the joint actually needs, which is clamp force. When one bolt in a circle is pulled to full torque first, it pinches the joint on that side, and the bolts tightened later do not see the same conditions. The result can be uneven clamp force, a gasket that seals on one side and leaks on the other, a cover that is not seated flat, or bolts that lose preload in service. Tightening in a cross or star pattern and in stages spreads the load around the joint so the faces close evenly.

How much clamp force a given torque produces depends heavily on friction under the head and in the threads. That is why a torque instruction has to say whether threads are dry or lubricated and with what, and why changing the lubricant, coating or fastener supplier can change the joint without anyone touching the torque value. Those decisions belong to the design engineer; the work instruction makes sure the assembler applies them the same way every time.

Where the values come from

The final torque, the lubricant and the number of passes come from the drawing, the assembly specification or the equipment manufacturer. Guidance such as ASME PCC-1 for pressure flanges describes tightening patterns and pass methods in detail; read it rather than a summary if your joint falls under it. The bolt torque calculator shows how torque, diameter and friction relate when you are checking a spec, and the torque specification guide covers how to document the value itself.

Example: 8-Bolt Cover Torque Sequence

Example This work instruction is for Example Manufacturing Co., a fictional maker of gearbox assemblies. The torque, pass percentages and part numbers are example values, not recommendations. Use the values on your own drawing or assembly specification.

Download this example (.docx)

Tools, materials and PPE

• Click-type torque wrench, range covering the final torque, inside its calibration date
• Bolts, washers and gasket at the part numbers on the bill of materials
• Lubricant named on the drawing; lint-free wipes; thread chaser
• Torque-seal paint marker
• Safety glasses; gloves while handling the gasket and solvent

Steps

1. Check the wrench and the parts. Confirm the torque wrench calibration label is in date and its range covers the final torque. Check the bolts, washers and gasket against the bill of materials.
   Key point: Use the wrench in the middle of its range where possible. Record the wrench ID on the traveler.
   Reason: An out-of-calibration wrench or the wrong grade of bolt gives the right reading and the wrong clamp force.
2. Clean and prepare the joint. Wipe the cover and housing faces clean. Run a thread chaser through any tapped hole that shows debris or damage. Fit a new gasket.
   Key point: Faces free of old gasket, burrs and oil. Gaskets are not reused.
   Reason: Debris or a damaged thread absorbs torque, so the bolt reaches the reading without reaching its clamp force.Safety: Wear gloves when using solvent and keep it away from ignition sources.
3. Lubricate as specified. Apply the lubricant named on the drawing to the bolt threads and under the head, or leave them dry if the drawing says dry.
   Key point: Same lubricant, same amount, every bolt. Never substitute a lubricant.
   Reason: Friction sets how much clamp force the torque produces; changing it changes the joint.
4. Install and snug all bolts. Fit all 8 bolts and run them down by hand until each head just contacts its washer.
   Key point: Every bolt started by hand before any is tightened. A bolt that will not turn by hand is cross-threaded; stop and remove it.
   Reason: Seating the cover evenly first stops one side being pulled down ahead of the other.Safety: Keep fingers out from under the cover edge while it seats; it is a pinch point.
5. Tighten in the star pattern, pass 1. Number the bolts 1 to 8 clockwise. Tighten in the order 1-5-3-7-2-6-4-8 to 30% of final torque, 7.5 N·m (example values).
   Key point: Follow the sequence diagram on the station. Each pass goes all the way around before the next starts.
   Reason: Opposite bolts pull the faces together evenly instead of tilting the cover.
6. Tighten in the star pattern, pass 2. Repeat the same sequence at 60% of final torque, 15 N·m (example values).
   Key point: Same order as pass 1. Do not skip to full torque.
   Reason: Stages let the gasket compress gradually so each bolt keeps its share of the load.
7. Tighten to final torque, pass 3. Repeat the same sequence at 100%, 25 N·m (example value). Pull smoothly until the wrench clicks once, then stop.
   Key point: One steady pull to the click. No jerking, no second pull past the click.
   Reason: A jerk or a second pull overshoots the torque.Safety: Brace your stance and keep your hands clear of edges in case the wrench slips. Never extend the wrench with a pipe.
8. Check pass and mark. Go around the circle clockwise at final torque. If any bolt turns, re-torque it and check its neighbors. Mark each bolt head and the cover with a torque-seal stripe.
   Key point: Check pass is clockwise, not the star order. Mark only after the check pass.
   Reason: Earlier bolts can relax as later ones are tightened. The stripe shows the joint was finished and shows if a bolt later turns.
9. Record the joint. Record the final torque, wrench ID and your initials on the traveler.
   Key point: Record what was done, not just “OK”.
   Reason: If the joint leaks or loosens, the record shows which wrench and spec were used.

Acceptance criteria

• Wrench in calibration, ID recorded on the traveler.
• All 8 bolts tightened in three passes in the star sequence to the drawing torque (example: 25 N·m).
• No bolt turned on the clockwise check pass, or any that turned was re-torqued and its neighbors checked.
• Every bolt carries an unbroken torque-seal stripe across head and cover.
• Cover seated flat with the gasket visible evenly all round, and no damaged threads.

How to adapt this example

Copy the steps into the blank work instruction template, or edit the .docx above. Change the joint description, bolt count and pattern to your part, and take every value from your drawing or specification. Put a numbered sequence diagram of your own joint at the station, drawn from your bolt pattern; the bolt circle calculator gives the hole positions if you are drawing it to scale.

• For a different bolt count, number the bolts around the circle and work out an opposite-pairs order for that count, then have engineering approve it.
• If your spec calls for torque-plus-angle, a torque-to-yield bolt or a tension tool, replace the passes with that method. It is a different instruction, not an extra step.
• Add a re-torque step only if the specification calls for one, with its timing.
• Keep the wrench on your calibration log so the in-date check in step 1 is easy to do.
• Add photos of the stripe and the seated gasket to a visual work instruction.
• Review the steps against the method in how to write a work instruction.

Common mistakes

• Tightening one bolt to full torque before the rest. Snug them all, then tighten in passes in the cross pattern.
• Not saying whether threads are dry or lubricated. Name the lubricant, or say dry, in the instruction and on the drawing.
• Writing “torque to spec” without the spec. State the value and its source, or point to the drawing note that holds it.
• Marking bolts before the check pass. Stripe only after the final check pass confirms no bolt turns.
• No wrench ID on the record. Record the wrench ID so a bad calibration result can be traced to the joints it touched.

Frequently asked questions

Sources

1. ASME PCC-1, Guidelines for Pressure Boundary Bolted Flange Joint Assembly, ASME
2. VDI 2230 Part 1, Systematic calculation of highly stressed bolted joints, VDI
3. ISO 6789-1, Assembly tools for screws and nuts — Hand torque tools, ISO
4. Machinery’s Handbook, Industrial Press

See also

• How to write a work instruction (Work Instructions pillar)
• Blank work instruction template (.docx)
• Bolt torque calculator
• Torque specification guide
• Calibration log template
• CNC machine setup work instruction example
• MIG welding setup work instruction example
• Packaging and labeling work instruction example
• Cleanroom gowning work instruction example