Water Claims – Copper Pipes and What Can Go Wrong
August 23, 2023 | By: Dinu Matei
The use of lead piping in plumbing systems can be traced back over 2,000 years. Romans used lead and clay piping to supply potable water to private homes, amphitheaters, and bathhouses and lead continued to be the material of choice for water supply lines until WW2. Upon the discovery that lead was leaching out of the pipes’ material, contaminating the water and causing lead poisoning, it ceased to be used as a material for water supply lines and was replaced with copper and galvanized steel. Galvanized steel was also retired not long after, due to issues with rust and corrosion, and copper became the material of choice. Copper is easy to work with, it comes in soft (annealed) and hard forms, and for many years it was considered the gold standard for water supply lines.
It has been estimated that in 2018 the annual world production of copper tubing used in water distribution systems was approximately 500 million kilograms (or 500,000 tons), which is equivalent to about 1.25 million km of pipe (enough to wrap around the Earth’s Equatorial circumference 31 times!).
In recent times, various polymeric materials, especially flexible PEX, have slowly begun to replace copper as the material of choice for water supply lines. Their low cost and ease of installation being too advantageous to ignore despite copper having a longer lifespan. Still, copper has its place in the industry, and it will continue to be used in water-carrying pipes for many years to come.
Copper tubing comes in four types based on the pipe wall thickness relative to the diameter of the pipe; K, L, M, and DWV (drain-waste-vent). Type K has the largest wall thickness to pipe diameter ratio, and it is usually used for applications where extreme strength is needed. The DWV type has the lowest wall thickness to pipe diameter ratio, making it suitable only for drain and vent lines as it cannot withstand the water pressure of most municipal water supply systems. Copper types L and M are the pipes most often used for standard pressurized water supply pipes.
Copper tubing can be connected in several ways: sweat-soldering, brazing, compression fittings, and push-in-style fittings (e.g., Shark Bite).
While most experts agree that copper is the best available material for water-carrying pipes, copper pipes and copper pipe connections still regularly fail, and will continue to fail in service, causing extensive property damage and expensive insurance claims. Investigating copper pipe/connection failures can be an extensive and complex process. The most common causes for copper pipe/connection failures seem to be associated with installation deficiencies and freezing. However, there are many more failure modes and causes which will be presented below.
- External pitting corrosion: Joining of copper tubing/fittings by means of soldering is governed by the “ASTM B828 Standard Practice for Making Capillary Joints by Soldering of Copper and Copper Alloy Tube and Fittings”. One of the steps outlined in the Standard deals with cleaning the contact surfaces by using a so-called flux, which is a corrosive chemical compound. If the surfaces are not cleaned after applying the flux, it will remain on the surface of the tubing and it will eventually start to corrode the pipe, a condition which will create pinhole perforations.
- Improper Solder Connection: One of the conditions necessary for a soldered joint to exhibit good strength is to have an adequate contact area which can be accomplished by ensuring an adequate depth. There is another Standard that outlines the requirements of a soldered joint depth as a function of the tube size, “ASME B16 Wrought Copper and Copper Alloy Solder-Joint Pressure Fittings Standard”. If the depth of a soldered joint is too shallow – below the Standard requirements – the strength of the joint will be significantly diminished, making it prone to failure. The conformance of the joint depth with the standard requirements can be checked by simply measuring the depth of the joint, which requires no special techniques or tools. Photograph 1 illustrates the appearance of a typical shallow depth of joint and photograph 2 illustrates a “solderless” connection, where the installer simply forgot to do the soldering; it was a snug fit connection that separated because in this condition it could not withstand the water pressure. Contact surface preparation is also critical for a good soldered joint. If the contact surfaces (tube ends and fitting cups) are not cleaned of debris, oxides and oils, they will interfere with the capillary action of the solder alloy and the joint will exhibit a poor wetting condition, making it weak and prone to failure. This condition can be easily checked by the naked eye or by the use of a stereo microscope. If there is no solder alloy on the contact areas, and the pipe substrate is exposed and visible, this means that the contact surfaces were not properly cleaned prior to the joining process. A substandard soldered joint is illustrated in photograph 3.
- Galvanic Corrosion: When two dissimilar metals are placed in direct physical contact and there is humidity in the contact area, the less noble metal will start to corrode. Contact between galvanized steel or aluminum, and either copper or brass, is a setup for rapid corrosion, especially in a humid environment. This condition could also be checked visually without the need for special equipment, as seen in photograph 4 where the copper pipe is in direct contact with the steel framing.
- Bowing: This condition is sometimes encountered in risers associated with HVAC systems in high-rise apartment buildings. The risers, which extend many floors up from the mechanical room level, are made from several sections of copper pipe. If these sections are not cut to the proper size and are left too long, they tend to bend in service, a condition which will introduce both undesirable tensile stresses in the concave section, and compressive stresses in the convex section. Often, the bowing of a riser is visible to the naked eye. A copper riser that was bent in service and which developed a longitudinal split as a result is shown in photograph 5.
- Improper Copper Pipe/Fitting: As mentioned earlier, copper tubing and fittings come in four types. A plumbing designer will recommend a specific type to accommodate the particular service conditions. A DWV pipe/fitting is not suitable for applications where pressure is a factor for the simple reason they are not designed to withstand pressure and the pipe/fitting might split. The wrong choice of material can be determined by looking at the markings stamped or printed on the component, which clearly read “DWV,” as seen in photograph 6.
One of the leading causes of copper/fitting failure in service is freezing. Freezing can occur for many reasons and in various scenarios. When freezing occurs in a copper plumbing system, either a longitudinal split forms in the pipe, usually in an elbow section (as shown in photograph 7), or at a poorly soldered joint. The split in the pipe exhibits typical characteristics like a fish-mouth appearance and outward bulging around the rim. Although the split and macro features can be seen by the naked eye, sometimes further microscopic examination is required to determine whether there was a manufacturing defect within the material. Soldered joints forcefully separated by freezing can be distinguished by the presence of longitudinal markings on the separated contact surfaces.
Stress Corrosion Cracking
Stress corrosion cracking (SCC) is a progressive degradation mechanism that occurs in metals and alloys as a result of the simultaneous presence of tensile stress, a corrosive environment, and a susceptible material. In the absence of one of these three components, SCC will simply not occur. Failures due to SCC can be very unpredictable. They can occur after as little as a few hours of exposure. Conversely, the piping may continue to function normally for months or even years. SCC of copper pipes is often encountered in risers associated with HVAC systems in high-rise apartment buildings and a full metallurgical evaluation is required to reach a definite conclusion. There will be secondary and branched cracks in the material (as seen in photograph 8) and the fracture surface will be either transgranular (through the grains), or intergranular (along the grain boundaries, as seen in photograph 9).
- Erosion, or velocity-induced corrosion, is described as localized wearing away of pipe material due to the impingement of foreign particles/air bubbles in the water against the inner diameter of the pipe, or due to cavitation. The erosion corrosion degradation is more predominant in areas where there is a change in the direction of the water flow, or where there is turbulent flow caused by a change in the pipe diameter. Areas of the pipe affected by erosion corrosion exhibit wall thinning, are typically bright and shiny, and exhibit grooves or rounded cavities as seen in the example illustrated in photograph 10. The cavities will grow over time and will develop into pinholes in the pipe wall.
- Improper Water Treatment Chemistry: Chemicals like chlorine and/or chloramine are often added to public water systems to act as disinfectants in potable water. In some municipalities, where attempts were made to counterattack acidity (adjustment of pH), sodium hydroxide was added to the water. However, this created favourable conditions for copper to corrode, and as a result, copper pipes developed pin holes (through wall perforations), an example being illustrated in photograph 11.
- Water Hammer: Water hammer is a phenomenon that can occur in any piping system where a fluid in motion is forced to change direction or stop abruptly. This will result in a transient pressure surge, or high-pressure shockwave that propagates through the piping system causing it to burst at the weakest location. The pressure created during a water hammer effect is many times more than the pressure rating of the pipe/fitting and this may explain the pipe burst. The appearance of a burst due to water hammer can take many forms, however, it is clearly distinguishable from a split that occurred as the result of freezing (i.e., flared opening, gasket extruded through a joint). Water hammers occur in every plumbing piping system; the noise of rattling pipes following the flushing of a toilet, for example, is evidence of water hammer.
Stray current corrosion
Stray current is an electrical current that flows through paths outside the intended electrical circuit. It creates an electrical potential between two metallic components that should not be subjected to voltage. It can be caused by wiring flaws (electrical equipment not properly grounded), or underground metallic structures close to piping. Corrosion is an electrochemical process involving an anode (a piece of metal that readily gives up electrons; corrodes), an electrolyte (a conductive media that helps electrons move) and a cathode (a piece of metal that readily accepts electrons). In stray current corrosion, the piping becomes the anode and will therefore corrode over time. Damage caused by stray current corrosion is usually localized, and it can be identified by the presence of rounded crater-like features on the surface which eventually grow, overlap, and cause wall perforations. Photograph 12 illustrates a section of a copper pipe that was consumed by stray current corrosion.
Intentional damage (insurance fraud)
I have seen many instances where attempts were made to deceive insurance companies for financial gain. This has included piping/fittings intentionally altered and submitted as a claim, posing as an installation issue or a manufacturing defect that caused the incident. One example is the pipe section illustrated in photograph 13. The homeowner used a pipe cutter to make a partial circumferential cut on the copper pipe. Being weakened by this process, it was only a matter of time before the split opened, creating the pathway for water to discharge. The claim was eventually denied, but not before a comprehensive fractography analysis under a powerful microscope and metallurgical evaluation were conducted to rule out an installation issue, overpressure, or a manufacturing defect.
Manufacturing defects, such as voids, pores, impurities, and non-uniform microstructure, all of which reduce the load-carrying capability of the pipe, will act as undesirable stress concentrators. Such defects can be identified only by destructive examination and metallurgical evaluation of microstructures. A metal/alloy microstructure is the result of the material chemical composition and processing history, and it will dictate the final properties of the material and/or the component manufactured from the material. There are specific heat treatments for each family of alloys to tailor the microstructures to the desired level. Smaller grains are desired as this condition will increase the strength of the material while a large grain microstructure will have a detrimental effect on the strength and toughness of the material. Although the grain size is controlled at the manufacturing stage, sometimes variations from the desired microstructure are encountered, such as the example illustrated in photograph 14.
Dinu Matei, Consulting Forensic Engineer M.Sc., P.Eng.
Dinu specializes in metallurgical, materials and mechanical failure analysis. During the course of his career, he has been involved in more than 700 failure investigations of various metallic and non-metallic components, and in 23 projects leading to the development of new materials and processes.