Know your standards: AWWA to release new standards for concrete pressure pipe installation

Transmission mains are a costly and important investment for communities, and proper installation is a critical first step to protecting this investment. Leveraging lessons learned from almost 100 years, The American Water Works Association (AWWA) will release a new standard for concrete pressure pipe (CPP) installation in 2025. The standard will help utilities and contractors identify and prevent installation defects.

Independent inspection is an important best practice outlined in the standard that will greatly extend service life. Quality assurance and control measures are critical during the early stages of a pipeline’s life, from manufacturing to installation and commissioning. During design, utilities can also enable inspection and real-time monitoring for a fraction of the cost of future retrofits, laying the foundation for long-term reliability.

What is concrete pressure pipe?

Made of concrete and steel, CPP is a durable, reliable, and economical pipe that is resistant to corrosion and physical damage and available in a wide range of diameters. There are four common types of CPP covered by the new standard, including:

• Reinforced concrete cylinder pipe (AWWA C300)
• Reinforced concrete noncylinder pipe (AWWA C302)
• Prestressed concrete cylinder pipe (AWWA C301)
• Bar-wrapped steel cylinder pipe (AWWA C303)

Protecting your investment

At Xylem, we’ve observed the damage and studied the cause of many of the largest CPP failures in North America over the last 30 years. Most of those premature failures resulted from manufacturing defects or improper handling, joining, or embedment during installation. As we look forward to the new standard, below are five ways to protect your CPP investment:

1. Manufacturing

Close manufacturing oversight and periodic lab testing help ensure quality pipes that meet standards and specifications.

Poor manufacturing processes have caused some of the industry’s most catastrophic pipeline failures. Today, utilities are still facing the consequences of faulty class IV wire, which has led to hydrogen embrittlement and higher rates of failure in prestressed concrete pipes. We also frequently see generalized corrosion of reinforcing steel from chloride penetration due to improper moisture content or volume of permeable voids in applied mortar coating. These examples show that the performance and longevity of a pipeline start with sound manufacturing long before the first pipe is laid.

2. Handling

Following the standard’s best practices for handling and visually inspecting pipes for damage after delivery could prevent a failure down the line.

Damage to a pipe’s coating and lining during transport and delivery can result in corrosion of its structural steel components. Installing large-diameter pipes is challenging work due to their size and weight. A crack from dropping a pipe or a nick from a backhoe can eventually become the origin point of a failure, even while the rest of the pipeline remains in good condition.

3. Pipe joints

Properly gasket, secure, and rotate pipe joints to ensure a watertight fit and proper thrust restraint.

We recently identified a leaking pipe joint with a rolled gasket from its installation many decades ago. Joint leaks may start as a relatively small problem, but they can eventually damage the pipe wall and cause sinkholes. Pipe joints that are over-deflected or restrained improperly can cause bending forces that shear a CPP barrel. It's also very common to see premature degradation of steel joint rings where installers applied external concrete grout diapers or internal cement mortar in a hurry and didn’t achieve full coverage.   

4. Embedment

Embedment provides a pipe with critical support and prevents damaging external loads.

Construction contractors should pay close attention to designs, as the embedment’s strength depends on soil class and compaction, trench geometry, and depth. Installers should ensure the bedding and embedment are free of rocks, organic matter, and other material that could cause uneven settling or point loads. Flat trenches, rock pinnacles, or uneven subgrade materials as well as quick backfill around the haunches of a pipe provide uneven support and often lead to premature CPP failure.

With internal inspection, it is common to see deflection and longitudinal cracking at the crown and invert of a CPP due to excessive external loads. Installers can prevent overloading new pipelines by following the standard’s guidance for using compaction equipment over top of the pipe. Installers should also avoid driving heavy machinery over shallow pipelines.

5. Inspection & monitoring

Inspection and monitoring ensure that new CPP is in the best possible condition, minimizing the risk of premature failure and protecting a utility’s investment now and into the future. 

The new standard recommends verification testing by a third-party. Visual inspection can ensure that pipes are free of structural cracks and other damage, proper bedding is achieved, and joints are made and grouted correctly. Electromagnetic inspection ensures the integrity of each pipe’s internal steel reinforcement and can be performed before or after pipes are installed.

When designing and installing new pipelines, utilities should consider adding access points and other features to prepare pipelines for future inspections. The cost is negligible compared to material and installation budgets, and utilities can reap major benefits down the line. Going one step further, pipeline owners can install a real-time threat monitoring system from day one.

Recently, a prestressed concrete pipeline 96-inches in diameter began failing shortly after commissioning. The utility’s fiber optic monitoring system immediately identified the problem. Targeted forensics showed that a section of the pipeline was manufactured improperly. Without active monitoring, the issue could have gone undetected for years, eventually resulting in a catastrophic failure.

The cost of adding continuous monitoring is small compared to purchasing the pipeline. The service not only protects your investment, it enables utilities to track degradation and institute predictable management strategies over the life of the asset.