The Retainer Nut That Shorted a Firing Head and How It Changed Our Gunstring Protocol

Posted on by Crissa Fel Tawadan

Not every misrun ends in a dramatic misfire or stuck string. Sometimes, it’s quieter than that. Sometimes, it’s a single thread on a single retainer nut that unravels your entire plan.

That’s exactly what happened on one of our pump down perforating runs. The kind of job we’ve done hundreds of times. The wireline truck was rigged up, logging cable spooled, and the cased hole wireline tools were prepped for a quick plug set and perforation. Everything passed the switch tests—at first.

But once we ran the gunstring in hole for the second stage, something changed. The system showed a short at the igniter. We pulled back, rechecked everything, and tried again. Still short. Eventually, we had to bring the string back to surface.

That’s when we saw it—the EBTW retainer nut had backed off inside the switch sub, shorting the igniter pin to ground.

The Silent Saboteur: A Loose Retainer Nut

We’d set the retrievable bridge plug just fine during the first run. But when we built the next string, a fresh setting tool was attached to the same head.

The string passed initial switch tests, which is what made the eventual short so frustrating. It wasn’t until we got downhole—fully rigged up and pressurized—that the short circuit showed itself.

The cause? That little retainer nut had come loose, grounding out the contact post and cutting off the ignition path. The gun couldn’t fire, and we were seconds from calling in a full fishing wire line crew had we not caught it quickly.

The Root of the Problem: Hand Tightened Hardware

During the investigation, the builder admitted that the retainer nut had only been hand-tightened—a common habit for that particular trailer crew. No torque tool. No wrench. Just hand snug.

And that’s where things had gone wrong. In the high-vibration environment of a horizontal wireline run, hand-tight simply doesn’t cut it. It was only a matter of time before that nut worked its way loose.

This failure forced us to revisit our assembly procedures—and it’s why our gun building SOP now includes mandatory tool-based torque tightening on every retainer nut.

Retainer Nut Tightening Procedure: The New Standard

We created a set of clear action items to prevent any future shorts due to backing nuts. It’s now part of every string assembly, from wireline perforating to formation evaluation setups.

Gunstring Retainer Nut SOP

1. Hand Tightening Is No Longer Accepted

  • All retainer nuts must be tightened using a proper mechanical tool.

  • Hand snugging is not allowed—even as a placeholder.

2. Approved Tools Only

  • Use adjustable wrenches, socket sets, or box/open-end wrenches.

  • Do not use Scotchlok pliers or similar gripping tools that can round out the nut.

3. Issue Correct Wrenches to All Trailers

  • We’ve now standardized on 1” offset open-end wrenches across all trailers.

  • Each gun room has designated torque-check areas for final inspection.

4. Inspection Checklist for Every Build

  • Each gun builder must sign off on retainer nut torque before the string leaves the bench.

  • Visual inspection is logged and verified by the engineer during rig-up.

Why It Matters in the Wireline Services Oil and Gas Industry

In cased hole logging, where wireline well logging is done under pressure, you don’t get many second chances. A small internal short caused by a loose nut can derail:

  • A perforation well sequence

  • A full firing head assembly

  • The integrity of a cement bond log (CBL log)

  • A job using high-pressure wireline control systems

Misfires delay wireline services, cost thousands in lost time, and reflect poorly on any wireline provider—especially when clients expect flawless execution.

Lessons Brought Into Our Wireline Courses

We now teach this lesson in every one of our wireline courses that covers gun building and tool prep. Trainees learn:

  • The physics behind internal tool shorting

  • How vibration impacts threaded connections in horizontal wireline runs

  • Why visual inspection isn’t enough without mechanical torque

  • How improper wireline equipment prep increases NPT

Hands-on training includes side-by-side builds with and without properly torqued nuts, letting new techs feel the difference and understand how that “extra quarter turn” can make or break a run.

Supporting Safer, Smarter Wireline Operations

This updated protocol isn’t just for wireline perforating guns. We apply this to every component that includes mechanical contacts, including:

  • Production logging services

  • CBL and caliper log tools

  • Downhole camera systems

  • Tracer tech deployments

  • Any build involving quick-change connectors or switch subs

By locking down the assembly step, we’ve increased our wireline service reliability and decreased tool-related misruns across the board.

Final Thoughts – It’s Not Just About Tight, It’s About Right

There’s a reason we don’t hand-tighten tool joints. We know the risks. But for some reason, the same standard hadn’t been applied to retainer nuts—until now.

If you’re running a wireline company, maintaining wireline trucks, or leading crews in the wireline oilfield, this is your moment to implement smarter builds.