There is no one-size-fits-all approach to condition assessment. A successful approach uses the right mix of methods to cost-effectively reduce risk. Today we’re looking at whether spot checks deserve a place in the toolbox for managing prestressed concrete cylinder pipe (PCCP).
Spot checks typically involve excavating and exposing a buried pipeline and performing various analyses on the pipe material, coating, or surrounding soil. Spot checks are usually performed in areas of concern following a preassessment.
For metallic pipelines, spot assessments can be an economic approach to checking areas of likely corrosion. However, they provide utilities with limited data and may not represent conditions at other locations along the pipeline. This is especially true for PCCP.
Spot checks on PCCP are largely unreliable due to the way this pipe material degrades.
Condition data shows us that deterioration is not uniform along a PCCP pipeline. Only about four percent of inspected pipes show indicators of distress. This means spot checks could easily miss the small percentage of pipes that are deteriorating or nearing failure.
Identifying PCCP degradation using desktop analysis or above-ground corrosion surveys is like searching for a needle in a haystack.
Inline inspections can provide pipe-by-pipe data, so utilities can pinpoint the often random and localized issues that lead to PCCP failures. An external electromagnetic inspection, shown here, can validate damage on excavated pipes before repair or replacement.
Overline corrosion potential surveys and soil sampling can indicate hot-spot areas where stray currents and acidic soils could lead to PCCP degradation. However, results show that these tests have low-to-moderate correlation with actual PCCP condition.
PCCP is highly resistant to corrosion when manufactured properly. Steel prestressing wires — the primary structural component of PCCP — are embedded in an alkaline mortar coating. Corrosion of the prestressing wires typically occurs when the pipe’s protective mortar coating is damaged.
A PCCP segment sitting on a rock pinnacle could crack the mortar coating and cause heavy corrosion of the prestressing wires in an otherwise benign environment. A spot assessment is likely to miss this damage.
Electromagnetic inspection of an entire PCCP pipeline can find these often random and localized issues. Inline assessment tools give utilities a more complete understanding of the pipeline’s condition with data on each distressed PCCP segment.
When inspection data reveals patterns of deterioration, a root-cause analysis can help utilities understand the underlying reasons and develop a strategic management plan. This is where desktop analyses, corrosion surveys, and direct forensic evaluations of PCCP are most useful.
In summary, excavations for spot checks are expensive, disruptive, and the results are highly unpredictable when it comes to PCCP. Rather than generalize the condition of the pipeline, inline inspection tools provide precise pipe-by-pipe data. Utilities can use this information to perform targeted repairs, determine an asset’s remaining useful life, and build more defensible management plans.