Where's That Water From? (Part 1)

portrait photo of Rod

Rod Turk, P.E., CFEI

Where’s That Water From?

Part 1- PEX pipe fittings

Even small water leaks into buildings can come with large repair bills. Small, slow leaks—sometimes referred to as “stealth” leaks—can lead to structural damage, wood rot and biologic growth. Large floods cause more obvious and widespread damage. Either of these types of leaks can be caused by many different mechanical systems in buildings. In this four-part series, we will examine common causes of water damage from mechanical systems.

Polymer-Based Plumbing Systems

To reduce the cost and skill required to install plumbing, polymer-based plumbing systems were introduced to the United States in the 1970s. Early offerings in polymer plumbing systems were fabricated of polybutylene (PB) that suffered from manufacturing defects, misapplication, and chemical degradation. As such, PB has faded from prominence in potable water systems. Instead, later market entrants have relied upon cross-linked polyethylene tubing (PEX) and metallic or polymer fittings and clamp rings. The metallic rings of these fittings are attached using compression, while the polymer rings are expanded prior to assembly.

PEX Creep

PEX, like most polymers, is subject to creep (deformation over time) which can make mechanical joints prone to leaks in the long term. To address creep, the polymer is often captured between two rigid pieces (a nipple and a crimp ring) to make a fitting.

Figure 1

Crimp-Style PEX Fittings

The crimp style fitting (see Figure 1) compress a metal ring circumferentially inward, deforming the ring into the outer surface of the tube. This captures the tube wall between the ring and the nipple.

The advantage of the crimp connection is that it can be checked with gauges at the time of installation, and afterward, to validate proper installation. The problems that can occur with crimp connections are wear and misuse of the crimp tools and misplacement of the crimp ring.

Manufacturers provide installation instructions on the proper crimping of the rings. However, crimp tools are manual, and each size of tubing requires different sized jaws. Also, manufacturers require that the crimp tool be regularly calibrated using go/no-go gauges. Should the installer fail to check their installations, and the tool fall out of calibration, the result can be unreliable connections.

Clamp-Style PEX Fittings

Similarly, the clamp configuration deforms a metal band, shortening its length to provide a repeatable compression to the tube wall and affixing the tube to the nipple (See Figure 2). When properly applied, these fittings are watertight and reliable.

pipe clamp
Figure 2

The advantage of the clamp style connection is that the clamping action is the same regardless of the size of the fitting. As such, the installer need only purchase a single clamping tool for various sizes of fittings. The tool does need regular inspection, and proper installation is checked by use of a go gauge that assures adequate clamping of the “ear” at the gap. 

Expanding Tubing Around Fittings

Many professional plumbers find that expanding the tubing around fittings is preferable and less prone to installation errors than crimp- or clamp- fittings. Special expansion tools are used, and the tubing is reinforced with an exterior band of additional PEX. These reinforcement rings and polymer fittings are less costly than their metallic counterparts. The tubing and band are stretched from the inside and placed around the nipple of the fitting. The memory of the polymer (its tendency to return to its original size) shrinks the tubing onto the nipple, creating a leak-tight seal. (Figure 3) 

The advantage of this is that if the fitting is in the tube, and the exterior band is in place, you have a good (tight) fitting. Also, because the tube diameter is being increased at the fitting, there is less pressure loss in plumbing systems using this method. It is possible for the installer to over-dilate the tubing such that the polymer memory is not enough to create a tight seal. The most likely cause of leakage from this type of fitting is a lack of adequate seating of the tubing to the fitting. 

Polymer tubing
Figure 3

PEX Fittings and Dezincification

Another common issue for PEX fittings is that of dezincification—yeah, that’s a thing. Dezincification is the selective leaching of zinc from high-zinc bronzes (i.e. cheaper bronzes) caused by water chemistry and poor alloy choices from manufacturers. Some Zurn fittings were subject to class-action lawsuits involving the use of high-zinc fittings leading to both stealth leaks and flooding. This type of fitting malfunction is identified by the external appearance of corrosion products on the fittings as well as an open “sponge-like” appearance of the fitting metal under a microscope. In areas of aggressive water chemistry, or when used with demineralized (RO) water, manufacturers recommend polymer-based fittings.

There are many ways for the fittings and tubing of polymer pipe systems to cause either large or small leaks in domestic plumbing systems. By reviewing the installation, and the state of the affected fittings and investigators can determine the cause of the leak.

In part two of this series, we will look at common causes of leakage at the commode—the fun never ends!