Visual & Sounding Inspections

Visual and sounding inspections are a reliable method of detecting pipes in an advanced state of distress. Typically, these inspections are conducted in conjunction with an electromagnetic (EM) inspection.

Internal visual and sounding inspections require manned entry to the pipeline and dewatering of the pipeline. By combining the EM inspection data with the manned inspection, Pure’s engineering team can deliver an accurate report on the condition of the pipeline. Any pipes judged to be in a potentialstate of incipient failure will be immediately reported to the utility so replacement or rehabilitation can be performed while the pipe is out of service for the inspection.


The visual portion of the inspection consists of observing visible features and cracks that indicate potential distress; this requires experienced staff to know which cracks are normal and which are indicative of a problem. It also requires a thorough understanding of the width and length of cracks that are normally produced during the production of pipe as opposed to those that might indicate lack of prestressing wires, or distress, in the pipe.

The visual inspection also includes an examination of the joints, including the width of joints or theamount of pull the pipeline was subject to in order to maintain line and grade. All anomalies will be noted with the distance and location from known features.


The sounding portion of the inspection relies on impacting the interior surface of the pipe wall with a tapping rod and listening for hollow sounds that indicate delamination. Delamination is also an indication of a loss of prestressing wire in a pipe.

The Benefits of Visual & Sounding Inspections

  • Proven method of identifying pipes in a state of incipient failure. As prestressing wires break in a prestressed pipe, the pipe begins to expand. Since the concrete liner cannot expand, either a delamination or crack will form as the pipe approaches failure.
  • Provides an excellent lay schedule of pipe that is in the ground; as-built records often differ from in-ground pipe conditions.
  • Documents interior pipe conditions. Dimensions and photographs of cracks are provided and joint problems are documented.
  • Determines the condition of joints.
Visual sounding side one

A pipeline engineer travels through the pipe conducting a visual and sounding inspection

Visual sounding side two

Figure: Cracks on the interior of a pipe identified during a visual inspection. In many cases, cracks are not this obvious. A careful visual inspection is performed with people dedicated to the task and with considerable experience in these types of inspections.

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