Assumptions regarding structural damage are, in some instances, made erroneously. Operators of television equipment are looking for problems. These unintentional errors of judgment have frequently lead to conclusions about conditions which are either non-existent or of significantly less magnitude than originally indicated. These assumptions can become difficult to resolve.

THINGS TO KNOW BEFORE AND DURING TELEVISION INSPECTION –  Be professional in the methods used and be accurate in what is recorded by voice and entered into the written log. Extraneous conversation, background noise and speculation should be avoided.

Before the first observation is made, it is necessary for the operator to fully understand the operation and capabilities of the equipment. The camera must be placed as near the centerline of the pipe and in as straight alignment as possible. This reduces distortion caused by the wide-angle lens. The observations are distorted by the camera lens and light intensity. Keep in mind that what you see can be greatly exaggerated. The camera is not only looking down the length of the pipe, but because of the wide angle lens, looking at the sides of the pipe or into the joint at a steep angle.

SAGS IN THE LINE -  Pipe lines experience some settlement under load, which is due to the pipe bedding not the pipe itself After cleaning or testing, water may remain in the line for a lengthy period of time if the line is on a very flat grade. It may take a day or more for the water to drain to accurately expose low points in the line. Estimating the depth of water is very difficult.

JOINT OBSERVATIONS -  A "halo effect" may give the illusion of an offset, deflected or pulled joint. Also, the factory-trimmed ends of the pipe may present the illusion of an offset joint.

A gap at a joint does not necessarily indicate joint failure. The joint design for clay pipe provides an allowance for joint gap without sacrificing integrity. ASTM Standard C425 Compression Joints for Vitrified Clay Pipe and Fittings requires clay pipe joints to seal in angular deflection up to a specified maximum depending upon the pipe diameter. There will be a gap on one side due to the angular deflection. This is expected and acceptable.

BREAKS/CRACKS —  Be very careful in identifying breaks or cracks. This may be a structural situation requiring remedial measures at substantial cost. Marks on the inside of the pipe may only be cosmetic, caused by pipe handled with a fork lift, residual water lines from cleaning or sewage flow marks, and must not be mistaken for structural problems

SUMMARY -

• The operator’s comments are frequently interpreted by others as being much more accurate than the actual condition.
• The image as seen by the eye of the camera may be distorted
• The camera position may affect the distortion. Center the camera in the pipe and make sure the camera line of sight is parallel to the pipe invert.
• It is very difficult to determine specific dimensions because of the exaggerated view.
• The image of an offset joint is exaggerated by the pipe trim, any gap between pipe ends and the angle of the joint itself.
• Manufacturing and handling marks may appear to be structural problems.
• Manufacturing and handling marks may appear to be structural problems.
• Television inspection is a good tool. Let’s not ruin its effectiveness by exceeding its capabilities. Simply stated, you’ve got to KNOW YOUR LIMITATIONS.