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Quick answer: Charlotte Pipe’s recommended bolt torque for its PVC and CPVC flanges is 10–15 ft-lbs for 1/2″ to 1-1/2″, 20–30 ft-lbs for 2″ to 4″, 33–50 ft-lbs for 6″ and 8″, and 53–65 / 53–75 ft-lbs for 10″ / 12″. Tighten in the star pattern marked on the flange, 10 ft-lbs at a time, with a torque wrench, new bolts and nuts, and flat washers under every head and nut.
All steps and numbers here come from Charlotte Pipe’s Plastics Technical and Installation Manual (pages 31 and 68), read October 9, 2026 from the rendered pages. Charlotte flanges ship with a QR code sticker that points to these instructions. Other makers set their own torque; follow the one for your flange. This page has no buy buttons.
Charlotte’s flange bolt torque chart
| Pipe size | Bolt holes | Bolt diameter | Torque (ft-lbs) |
|---|---|---|---|
| 1/2″, 3/4″, 1″, 1-1/4″, 1-1/2″ | 4 | 1/2″ | 10–15 |
| 2″, 2-1/2″, 3″ | 4 | 5/8″ | 20–30 |
| 4″ | 8 | 5/8″ | 20–30 |
| 6″, 8″ | 8 | 3/4″ | 33–50 |
| 10″ | 12 | 7/8″ | 53–65 |
| 12″ | 12 | 7/8″ | 53–75 |
Charlotte notes its flanges meet the bolt-pattern requirements of ANSI/ASME B16.5.
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Installation steps
- Join the flange to the pipe by solvent cementing or threading. Because bolting puts tensile stress on a cemented joint, Charlotte says to double the recommended cure time before you bolt the flange up or pressure test.
- Gasket: use a full-faced elastomeric gasket that resists the chemicals in the line. Charlotte says a 1/8″ thick gasket with a Shore A durometer of 55–80 is normally satisfactory.
- Align: put all the bolts through the mating flange holes, with properly sized flat washers under every bolt head and nut.
- Tighten in sequence: follow the bolt pattern marked on the flange, in 10 ft-lb steps, up to the recommended torque. Use new bolts and nuts.
- Stop at the max. Don’t tighten so the flange ring bends or is under stress. Mate it only to full-face flanges or valves that meet ANSI B16.5 150 lb dimensions and support the entire flange face.
- Use a torque wrench, and thread lubricant to get a true reading. Confirm the lubricant is chemically compatible with the pipe and fittings.
- Buried flanges: where settling could happen, support the flange so it stays aligned in service.
Mistakes Charlotte warns about
- Over-torquing the bolts; Charlotte says it may result in component damage and system failure.
- Using the flange to pull piping together, or bolting up out of alignment.
- Skipping flat washers.
- Bolting to a flange or valve that is not full-face or does not support the entire flange face.
- In chemical service, plain steel hardware: Charlotte recommends corrosion-resistant bolts, nuts and flat washers.
Flange pressure rating
In Charlotte’s PVC Schedule 80 table, flanges are rated 150 psi at 73°F and 33 psi at 140°F in the listed sizes from 1/2″ to 12″ (the table lists none at 5″, 14″ or 16″). That’s well under the pipe: 1/2″ Schedule 80 PVC pipe is rated 850 psi at 73°F. Charlotte says the system must be de-rated to its lowest-rated component at the highest operating temperature.
Flange or union?
Both let you take a line apart. Charlotte’s union ratings stop at 3″, while its flange torque table runs to 12″, and Charlotte calls flanging an easy way to join plastic and metal systems. For small lines, see our PVC union installation guide.
FAQ
What torque for a 4 inch PVC flange?
Charlotte lists 20–30 ft-lbs for 4″ pipe, with eight 5/8″ bolts.
What torque for a 2 inch PVC flange?
Charlotte lists 20–30 ft-lbs for 2″ pipe, with four 5/8″ bolts.
What gasket goes on a PVC flange?
Charlotte calls for a full-faced elastomeric gasket that resists the chemicals in the line; 1/8″ thick with a Shore A durometer of 55–80 is normally satisfactory.
How long before I can bolt up a cemented PVC flange?
Charlotte says to double the recommended solvent cement cure time before joint assembly and pressure testing.
Related guides
Sources
- TM-PL (PDF) (charlottepipe.com), read 2026-10-09