Pipe Thread Sealant

Pipe thread sealant is a product used on threaded pipe connections to stop leaks. It works by filling tiny gaps between male and female tapered threads and by lubricating the joint so the threads seat fully without galling (metal tearing). You’ll see it used on NPT (National Pipe Taper) and BSPT (British Standard Pipe Taper) threads—both are tapered and rely on sealant to become leak-free. It’s not for straight threads that seal with a gasket or O‑ring.

Where You’ll Use It

Around the house and shop, you’ll use pipe thread sealant on:

• Water supply lines (faucets, shower arms, water heaters)
• Natural gas and propane piping
• Compressed air systems and pneumatic tools
• Hydronic heating and radiator connections
• Sprinkler/irrigation risers and manifolds
• Well and pump connections
• RV and marine plumbing (where threaded fittings are used)

Types of Pipe Thread Sealant

There are three main categories. Each has strengths and best-use cases.

1) PTFE Tape (Thread Seal Tape)

A thin, non-adhesive tape made from PTFE (polytetrafluoroethylene). It fills gaps and lubricates threads.

• Common colors and uses:
  • White: General purpose for water and air (residential sizes)
  • Yellow: Gas-rated (natural gas, propane)
  • Pink: High-density for water systems
  • Gray: For stainless steel (helps prevent galling)
  • Green: Oxygen-clean service (specialized)
• Pros: Clean, easy, immediate seal, no cure time. Great for small-diameter fittings.
• Cons: Can shred if applied poorly; not ideal for large industrial threads; some plastics can be overstressed by overtightening if tape is overused.

2) Paste/Compound ("Pipe Dope")

A brushable compound, often non-hardening, sometimes filled with PTFE or other lubricants. Formulations vary for water, gas, fuel oils, and chemicals.

• Pros: Stays pliable, seals minor thread imperfections, resists vibration, easy to adjust alignment during assembly.
• Cons: Some solvent-based products are not compatible with plastics (PVC, CPVC, ABS). Always check the label.

3) Anaerobic Liquid Sealants

Single-part liquids that cure in the absence of air and in the presence of metal ions. Common in hydraulic and pneumatic systems.

• Pros: Strong, reliable seal; resists vibration; won’t shred; excellent for stainless and brass; many are high-pressure rated.
• Cons: Requires clean metal threads; may need primer on passive metals; cure time before full pressure; generally not for plastic threads.

How to Choose the Right Product

Match the sealant to the job using these checkpoints:

• Medium: Water, gas, air, hydraulic fluid, fuel, oxygen—pick a sealant rated for that medium.
• Material: Brass, copper, steel, stainless steel, PVC/CPVC/ABS—verify compatibility. Use plastic-safe compounds on plastics.
• Temperature and pressure: Check the product’s spec sheet for limits.
• Code and label: Gas work often requires gas-rated products; oxygen service needs oxygen-clean sealants only.
• Size and accessibility: Tape is quick for small fittings; paste is helpful on slightly imperfect threads; anaerobic is great for clean metal where you want a tamper-resistant seal.

How to Apply PTFE Tape

1. Prep: Clean threads with a wire brush or rag. Remove old tape/compound and debris.
2. Direction: Hold the male fitting facing you. Wrap clockwise so tightening won’t unravel the tape.
3. Start position: Begin on the second thread from the end to keep tape out of the line.
4. Wrap count: 2–3 wraps for 1/2" threads; 3–5 wraps for 3/4" and larger; use high-density tape for bigger or rougher threads.
5. Finish: Press tape into the threads with your fingers, then assemble. Tighten to snug plus an additional turn or two as needed—don’t muscle it.

How to Apply Paste (Pipe Dope)

1. Prep: Clean the threads thoroughly.
2. Application: Brush a thin, even coat on male threads only. Avoid globbing; keep it off the first thread if possible.
3. Assembly: Thread parts together by hand to avoid cross-threading, then wrench to final torque. Wipe off any squeeze-out.
4. Timing: Most non-hardening compounds seal immediately for pressure testing. Follow the label for cure or set times if specified.

How to Use Anaerobic Sealant

1. Prep: Threads must be clean and dry. Degrease if needed.
2. Primer: On stainless steel or plated parts, use the manufacturer’s primer if recommended.
3. Apply: Put a small bead on the male threads and assemble promptly.
4. Cure: Many products achieve handling strength in minutes but need hours for full cure. Follow the data sheet before applying full pressure.

Common Mistakes to Avoid

• Using sealant on the wrong joint type: Do not use tape or compound on compression fittings, flare fittings, or any connection that seals with a gasket or O‑ring.
• Wrong product for the medium: Gas lines need gas-rated sealants; never use general-purpose products on oxygen unless clearly marked oxygen-safe.
• Overwrapping tape: Too many wraps can crack plastic fittings or prevent proper thread engagement.
• Wrapping the wrong direction: Counterclockwise wraps unravel during tightening and make shreds.
• Starting at the pipe end: Tape shards can enter valves and fixtures. Begin on the second thread.
• Mixing incompatible products: Combining tape and paste can be effective in some pro setups, but only if both are compatible with the medium and materials. When in doubt, use one product correctly.
• Overtightening: Tapered threads can split female fittings (especially plastic) or damage valves. Tighten until leak-free—no extra quarter-turns “just because.”
• Skipping surface prep: Dirt, oil, or old compound prevents sealing and curing.
• Ignoring cure times on anaerobic sealants: Pressurizing too soon can cause microleaks.

Maintenance and Rework

If you disassemble a threaded joint, remove all old tape or compound, clean the threads, and reapply fresh sealant. For leak checks on gas or air, use a soap-and-water solution and look for bubbles. Follow local codes for gas work and consider hiring a licensed pro for fuel gas installations.

Related Terms and Concepts

• Pipe dope: Common name for paste-type joint compound.
• PTFE tape: Also called thread seal tape; often nicknamed “Teflon tape.”
• NPT/BSPT: Tapered thread standards used with sealant.
• Straight threads: Threads that seal with gaskets or O‑rings, not with thread sealant.
• Threadlocker: A different product that prevents fasteners from loosening; not designed to seal pipe threads unless also labeled as a sealant.
• Anti-seize: Lubricant to prevent seizing at high temps; not a thread sealant.

Practical Examples

• Install a shower arm: Wrap 2–3 clockwise layers of white PTFE tape on the shower arm’s male threads, start on the second thread, and tighten into the wall elbow. Aim the showerhead, then snug slightly more to align.
• Hook up a gas dryer: Use yellow gas-rated PTFE tape or a gas-rated paste on the black iron to valve connection, following local code. Check for leaks with a gas leak detector or soapy water.
• Set up a shop air system: On brass and steel fittings for a compressor manifold, use high-density PTFE tape or an anaerobic sealant rated for compressed air. Pressure test before use.
• Join plastic to metal: When threading a PVC male adapter into a brass valve, use a plastic-safe thread compound or a few wraps of PTFE tape. Hand-tighten, then add a small wrench turn—avoid cracking the PVC.

With the right product, correct application, and a light touch on the wrench, threaded joints can be assembled quickly and stay leak-free for years.