Mainlining in Leak Repair: The Hidden Risk That Could Shut Down Your Facility

Industrial leak repair is a critical aspect of facility maintenance, especially in high-pressure or hazardous process systems. While injectable sealants offer an effective solution for stopping leaks, there exists a lesser-known but serious risk associated online leak repair: Mainlining.

In this article, we’ll explore what mainlining is, why it’s dangerous, and most importantly, how to prevent it using the right equipment, procedures, and engineering guidance.

What Is Mainlining?

Mainlining occurs when injectable sealant—intended to stay in the void between the leak enclosure and the pipe—enters the product stream inside the pipe. This typically happens when an active leak is not properly stopped or minimized before the sealant is injected.

When sealant crosses into the line, it can:

• Clog downstream filters and strainers

• Cause unplanned outages

• Damage process equipment

• Contaminate the product

In short, mainlining can take what should be a controlled, localized repair and escalate it into a costly and wide-reaching failure.

How Does Mainlining Happen?

The process of mainlining begins with a leak in the pipe that’s enclosed by a leak repair enclosure—typically a void fill-style. In a void fill style enclosure, sealant is injected to fill the void between the enclosure and the damaged piping. During this process, the sealant follows the path of least resistance. If the leak is active and hasn't been mitigated, the sealant can be pushed directly through the hole / crack and into the flowing product.

This is especially problematic in systems where:

• There’s a downstream filtration component

• The sealant isn’t chemically compatible with the process stream

Preventing Mainlining: Best Practices

Mainlining is a high consequence, but low probability risk if proper mitigation practices are followed. Here are some best practices to avoid mainlining:

1. Pre-Injection Leak Mitigation

The first line of defense is stopping or minimizing the leak before injection. A simple, widely accepted solution is a rubber patch and hose clamps, sometimes called a stopgap. This method physically blocks the leak, allowing sealant to remain in the enclosure.

Important Note:
The patch must be installed before taking measurements or conducting a 3D scan to ensure the enclosure fits properly over the patch.

Some limitations of elastomeric patches that may make them ineffective are the surface temperature of the piping and chemical compatibility with the service. Most elastomeric seals are temperature resistant up to 150°C (300°F). For high-temperature or aggressive chemical environments, specialized materials or alternative solutions may be needed.

2. Perimeter Seal Style Enclosures

When a patch isn’t viable, perimeter seal enclosures offer another effective safeguard. These are designed to seal around the leak site without relying on leak stoppage.

A typical perimeter seal enclosure includes:

• Inner rope packing

• Center injection groove

• Outer rope packing

Rather than acting as a fluid seal, the rope packings primarily serve as barriers that help contain the injectable sealant from extruding into the enclosure cavity and outside of the enclosure.

3. Volume Control & Injection Protocol

Sealant volume is not arbitrary—it must be calculated by engineering based on the void space between the enclosure and the pipe. Field technicians are trained to inject only the prescribed volume.

If the enclosure does not appear full after injecting the expected amount:

• Stop immediately

• Do not continue injecting

• Reconfirm volume calculations

• Engage engineering and the client

A built-in tolerance of about 10% over the calculated volume is often acceptable. Beyond that, further injection may indicate the sealant is entering the pipeline.

Risk vs. Reward: The Cost of Complacency

Although the likelihood of mainlining is low, the consequences can be severe—leading to expensive downtime, product contamination, and equipment failure.

Preventive Measures Are Always Worth It:

• Choose the correct enclosure style

• Always attempt to stop the leak when using void fill systems

• Strictly adhere to calculated sealant volumes

Final Thoughts

Leak repair is more than just patching a pipe—it’s about maintaining system integrity and protecting the broader facility. Mainlining is a rare but potentially devastating occurrence that every facility operator and contractor must guard against.

At My Engineering Ltd., we specialize in engineered leak repair solutions that are safe, effective, and tailored to your operational realities. If you’d like more insights like this, subscribe to our updates or join our mailing list linked below.

Stay informed. Stay operational. Stay safe.