Causes and Examples of Tube Defects

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ID pitting can occur in a variety of ways, most commonly through galvanic and/or biological corrosion. When pitting is detected early, additional tube cleaning and water treatment changes can be made to slow or stop its progression and prevent future tube failure.

ID scaling occurs when impurities precipitate out of water as it heats. Over time, scaling can form an insulating layer on the tube wall, dramatically reducing heat transfer capability and machine efficiency. Chemical cleanings can remove built-up scale, and water treatment changes can prevent its formation.

Mechanical wearing occurs when tubes vibrate excessively within their supports, etching the tube wall. Mechanical wear accelerates over time as the tube loses mass. Plugging off affected tubes from service will protect the overall machine should the tubes eventually fail.

Cracks can occur in tubes due to material defects, heat expansion stress, and metal fatigue. It is difficult to estimate when a cracked tube may eventually fail, thus, they are usually removed from service immediately when detected.

Freeze conditions in tubes can be caused by improper refrigerant recovery, obstructed water flow, or extremely cold ambient temperatures. Water expands as it phase changes into ice, eventually bulging and splitting tube walls open. Plugging or replacing these tubes are necessary to restore vessel integrity.

Although uncommon, defects can and do occur during the manufacturing process. These can range from minor finning imperfections to severe dents or gouges. We recommend that all chillers be baseline eddy current tested prior to start-up to find any such defects so they can be properly addressed before problems occur.