Consulting Engineers and Nondestructive Examination

Tubing is the most vulnerable component of a shell and tube heat exchanger. Its thin wall provides good heat transfer. However, there is little allowance for various forms of attack which can reduce the performance of the tubing. Some mechanisms which can degrade air conditioning tubing are ID pitting, fretting wear (vibration damage) and circumferential cracking at land transitions.

The associated piping is also susceptible to both ID and OD corrosion attack throughout the entire system.

HES employs non-destructive examination (NDE) of tubes and piping by electromagnetic and ultrasonic techniques, respectively, to determine their condition. These include:

• Eddy current testing of non-ferromagnetic tube alloys for both finned and prime (non-finned) applications.

• Ultrasonic thickness testing of various grades and wall thickness of carbon steel piping.

Since in-situ tube testing is as much an art as a science, the high degree of Heat Exchanger Systems (HES) test personnel's training and experience is considered a key element required to obtain the accurate results necessary for predicting heat exchanger tubing remaining life, particularly for heat exchangers in corrosive environments.

In addition to test personnel, HES's NDE services are supported by corporate heat exchanger and aqueous corrosion experts. Consequently, HES uses NDE techniques to determine defect type and severity and engineering analysis to assess problem cause(s).

NDE identifies the nature, severity, and location of tube defects and thinned areas of piping. This information, coupled with a knowledge of the materials in service plus the system design and operating experience often provides a sufficient basis for determining the failure mechanism. When it does not, heat exchanger tubes and/or sections of piping are frequently extracted to provide specimens for destructive root cause failure analysis which involves analysis by some of the following methods:

• Atomic absorption

• Metallurgical chemistry analysis

• Measurement of significant mechanical properties

• Microbiological/Biochemical Analyses

• Metallography

• X-ray diffraction

• Inductively coupled plasma spectroscopy

• Scanning auger microanalysis

• Electron spectroscopy for chemical analysis

• Infrared, organic carbon and biochemical analyses

Through the use of these analytical techniques, the causes of failures are identified in an unambiguous manner. Appropriate corrective actions can then be identified and a corrosion rate (remaining life) can be projected.

For additional information and/or a quotation please contact:

Robert J. Bell at (781) 337-9400

or email to:    rjbell@heatexsys.com