How to Cut Out and Repair a Pinhole Leak in Copper

Why this matters

A pinhole repair is a small job with one decision buried in it: is the hole the problem, or is it the first visible symptom of a pipe that is failing along its length? A clamp over the hole answers neither question. A coupling sweated onto pitted pipe a quarter inch from the hole answers it badly, and the customer calls back in three weeks with a leak two inches away, convinced the first repair failed. The cut ends you expose during the repair are the best evidence you will get about the rest of the run, and most of the value of this job is reading them.

This card is the repair itself. Whether this house needs a section replaced, a repipe or water treatment instead is decided in Pinhole Leak Assessment and Repipe Recommendation, using what you record here.

Make the area safe before you touch the pipe

Water in a ceiling. A drywall ceiling holding water can come down in a sheet. Before standing under a bulge, set a bucket, put on eye protection, and pierce the low point with a screwdriver to drain it. If the wet area includes a light fixture, a fan or a junction box, open that circuit's breaker and confirm absence of voltage at the fixture with a tester proven on a known live source before and after, per NFPA 70E Article 120 (current edition), before you reach into the wet cavity.

Bonding. Copper water pipe is often part of the electrical bonding path. Before cutting a section out, clamp a bonding jumper across the section you will remove so the path is never broken, and if a meter reads voltage across the planned cut, stop and call an electrician; that is a fault elsewhere, and it is theirs to find.

Old joints. Joints in a house plumbed before the late 1980s may carry lead-bearing solder, which federal law took off potable systems in 1986. Do not reheat an old joint you do not need to, keep the flame off neighboring joints with a heat shield, and wash your hands before eating or smoking.

Steps

1. Isolate and drain the section. Close the nearest branch valve that holds, or the main, and open a fixture below the leak to drain the line. Open a fixture above it to let air in so the line empties. Why: solder will not flow on a wet pipe, and even a press fitting is easier to seat in a pipe that is not running. Prove the isolation: the leak should stop dripping within a few minutes and stay stopped.

2. Locate the hole and look at its neighbors. Dry the pipe, then look along the run with a light. Pinholes announce themselves with a green or blue crust where water evaporated, a stain on the pipe below, or a ring of corrosion. Mark the hole. Note where it sits on the pipe (on a horizontal cold line, often at the bottom), what fitting is nearest, and whether there are other crusted spots within reach. Any second bloom on the same run changes the job, and you want to know before you cut.

3. Cut out a section with margin. Cut with a tubing cutter, a few inches each side of the hole, not tight around it. Why: corrosion that made one hole is rarely a single point; the margin puts your cut ends, and the couplings that will ride on them, out on pipe that has a chance of being sound. Ream the inside burr and deburr the outside of each cut end. A hacksaw leaves a ragged, out-of-square face that will not seat in a press fitting and makes the wall hard to read.

4. Read both cut ends before you buy into them. This is the step that turns a patch into a diagnosis. Look at the cut face with a light and measure the wall with a caliper at the top and the bottom of the pipe. Compare to the nominal wall for the pipe type, which is printed in the color-coded marking on the pipe if it is still legible:

Wall thicknesses are the nominal values in ASTM B88 for drawn water tube.

What the cut face shows:

• Even wall all the way around, smooth bore: sound. Join to it.
• Bottom noticeably thinner than the top, or pits and green or black nodules inside: the corrosion runs on past your cut. Cut back further on that side and read again.
• Thinning on the outside only, at a strap or where the pipe touches a duct: external corrosion or wear from that contact. Fix the contact or the strap, not just the hole.

Stop rule: if the second cut on the same side still shows pitting, the run is the problem, not the spot. Make the safest short repair you can on sound pipe, and write it up for the assessment.

5. Fit the new piece with repair couplings. Use the same type of copper as the run or heavier (Type L to replace Type M is fine; Type M to replace Type L is not). Repair couplings, also called slip couplings, have no internal stop, so they can ride fully onto the new piece and then back out over the old pipe. Mark the old pipe ends at half the coupling's length before you start; the mark is how you know each coupling is centered and not hanging half on the new piece. The two positions, before and after the slide:

 first: both couplings slid fully onto the new piece
 old pipe      new piece, cut to the gap      old pipe
========*===|[-------]------[-------]|===*========
        ^ mark, half a coupling     mark ^
          back from the old end
 then: each slid out until its edge meets the mark
========[===|---]----------------[---|===]========
          joint                    joint

6. Join by solder or press.

• Solder. Clean and flux both ends, heat the coupling, not the solder, and feed lead-free solder and flux (IPC 2021 or UPC 2021, as adopted) into the joint; the steps are in How to Sweat a Copper Water Joint That Passes First Time. Keep a heat shield between the flame and any framing or insulation, have an extinguisher in reach, and stay in the area for 30 minutes after the torch goes out. A pipe still weeping water from a passing valve will not take solder: get it dry or switch to press.
• Press. Press repair couplings work on a damp pipe and remove the fire risk in a ceiling bay. Mark the insertion depth on each end with the maker's depth gauge, press with the correct jaw, and check every mark is still at the fitting face. Pipe so thin the press jaw distorts it is pipe you should have cut back further; press fittings are listed for specific wall types, and the maker's instructions say which.

7. Restore slowly and check the rest of the run. Open the valve gradually with a fixture open to bleed air. Stand beside the joint, not in front of it, as pressure comes up. Then walk the exposed run end to end with a light and a dry towel.

Worked example: a cold line in a basement ceiling

A 3/4 in Type M copper cold line runs 14 ft along a basement ceiling. The homeowner found a drip onto the laundry. Static pressure at the laundry hose connection: 72 psi, inside the 80 psi limit at fixtures.

Isolate and locate. The branch valve held; the drip stopped in about two minutes. The pinhole sat at the 6 o'clock position, 22 in downstream of an elbow, under a green crust. No other bloom visible along the 14 ft run.

First cut. A 6 in section, 3 in each side of the hole. Readings at the cut ends against the 0.032 in nominal for 3/4 in Type M:

• Upstream end: top 0.031 in, bottom 0.030 in. Sound.
• Downstream end: top 0.031 in, bottom 0.022 in, with two small pits visible inside. The bottom wall was 0.032 minus 0.022, or 0.010 in below nominal, a loss of 0.010 divided by 0.032, about 31 percent. Not sound.

Second cut, downstream side only. Another 3 in off the downstream end. New reading: top 0.031 in, bottom 0.030 in, smooth bore. Sound. The stop rule did not trigger, because the second cut came up clean. Total section removed: 6 plus 3, or 9 in.

Join. A 9 in piece of 3/4 in Type L (wall 0.045 in, heavier than the M it replaces) and two press repair couplings. Each old end marked at half the coupling length; couplings slid fully onto the new piece, set, slid out to the marks, depth checked, pressed. The pipe was damp from the drained line, which is why press was chosen over solder in a ceiling bay full of joists.

Record. Pipe type M, 3/4 in, cold. Pinhole at 6 o'clock, 22 in downstream of an elbow. Wall loss at the bottom 31 percent at 3 in from the hole, sound at 6 in. Static 72 psi. This is the record the assessment card works from: a single hole with sound pipe 6 in away is a different conversation from a run that pits at every cut.

Finish test: no leak at full pressure

• Pressure. With the valve fully open and fixtures closed, the gauge at the hose connection returns to static (72 psi here). A repair tested while a fixture is running has been tested at a lower pressure than it will live at.
• Dry towel. Wrap a dry paper towel around each coupling for 10 minutes. Any spot means a leak; a press joint that weeps was not fully inserted or not pressed; one that was never pressed may be pressed if the maker allows it, anything else is cut out.
• The run. The rest of the exposed run checked with a light and a towel, no second leak, no new bloom.
• Bond. The bonding path is continuous across the repair before the jumper comes off: on copper repaired with copper fittings it is, but confirm nothing nonmetallic went in.
• Power. A circuit opened for a wet ceiling stays off until the cavity and fixture are dry and, where the fixture held water, an electrician has checked it; then restore the breaker and confirm the fixture works.

When the answer is not a repair

Three or more pinholes in a year in the same house, pitting at every cut, or pinholes on both hot and cold lines point at the water or the system, not at the pipe you are holding. Make the leak stop, record the cut-end readings, and route the rest to Pinhole Leak Assessment and Repipe Recommendation, which owns the repair-or-repipe call and the customer conversation that goes with it.

References

• ASTM B88, seamless copper water tube, for nominal wall thickness by type.
• IPC 2021 or UPC 2021, as adopted, for lead-free solder and flux on potable water; the press fitting maker's installation instructions for wall types and insertion depth.
• NFPA 70E, Article 120, current edition, for verifying absence of voltage near wet fixtures.
• See related: Pinhole Leak Assessment and Repipe Recommendation
• See related: How to Sweat a Copper Water Joint That Passes First Time