When more data isn't better: rethinking bar-wrapped pipe assessment
A conversation with Xylem’s Ikram Efaz on the team’s award-winning research into what drives failure in bar-wrapped pipe
At UESI Pipelines 2026 Conference, Ikram Efaz and co-authors Masood Hajali, Ashan McNealy, and Alan Bair were awarded Best Paper for "Failure Mechanisms of Bar-Wrapped Pipe: Evaluating Local Cylinder Corrosion Through Nonlinear FEA with Intact Bars." The paper, selected from over 100 high-quality, peer-reviewed papers, tackles the question of what to look for when assessing bar-wrapped pipe.
Q: Bar-wrapped pipe is a composite material where both the steel reinforcing bars and the steel cylinder do structural work. What made you question whether cylinder corrosion on its own could cause a pipe to fail?
The motivation for this study came from a practical problem facing the water industry. Over the past four decades, communities have installed thousands of miles of bar-wrapped pipe (BWP) across the western and southwestern U.S. and Canada. As these pipelines age, utilities are looking for ways to assess them while balancing cost and effort.
In BWP, the steel cylinder and reinforcing mild-steel bars act together as the primary load-carrying component. BWP typically fails due to corrosion of these steel components, with small leaks progressing into larger leaks or failure.
We've done a lot of validation work in the field, and what we’ve seen consistently is that the cylinder and bars function as an integrated structural system. We haven't seen significant cylinder corrosion without bar breaks or the reverse. With this study, we wanted to test whether severe cylinder corrosion alone could lead to structural failure of BWP.
The practical implication is to validate a simplified assessment approach: inspecting for reinforcing bar breaks and leaks. High-resolution inspection of the cylinder is costly and operationally demanding, often requiring dewatering of the entire pipeline. From the cylinder inspection you're getting more data, but is more data always better?
Q: You built 54 finite element analysis models to study localized cylinder corrosion on a 24-inch bar-wrapped pipe. What did you learn from modeling different corrosion scenarios?
We modeled the structural impacts of cylinder corrosion at the crown and springline of the pipe using finite element analysis (FEA). While keeping the bars intact, we increased the size and severity of localized wall loss.
We found that it takes severe cylinder corrosion to reach yield, the point where we would recommend a utility take action to prevent failure. Even with a relatively large 32-inch corrosion region, the pipe didn't reach yield until about 90 to 95 percent cylinder wall loss. Smaller corrosion regions were even less critical.
However, when we modelled bar degradation along with cylinder corrosion, the pipe reaches yield at substantially lower corrosion levels. That tells us reinforcing bar degradation is a particularly important indicator of immediate to near-term structural risk.
The models supported what we’ve observed in the field: the bars and cylinder act as an integrated system. So it’s not practical that you would see significant cylinder corrosion without measurable bar breaks.
Q: What does this mean for utilities in practice—how should they be thinking about their inspection strategy?
High-resolution inspections can identify early-stage cylinder corrosion, but small, localized defects don't necessarily mean the pipe is at risk of failing. If there are no leaks or bar breaks, then structurally, the damage probably doesn't warrant a repair. The utility can spend that money and effort on other priorities.
If you want to find at-risk pipes, this study supports using bar breaks as the primary indicator of distress supplemented by leak detection to identify through-wall cylinder corrosion. Xylem’s PipeDiver® can detect both leaks and bar breaks in one inspection, without taking the pipeline out of service. This approach targets the dominant failure mechanisms while reducing inspection complexity and cost.
Ultimately, it depends on the utility's risk tolerance and repair decision matrix. But the conclusion we came to is that more data is not always better, especially for bar-wrapped pipe. The right strategy balances accuracy, cost, complexity, and risk, and it should be aligned with the utility’s asset management goals.