In the power, petrochemical and oil/gas industry a big variety of heat exchangers is being used. Heat exchangers are being used to heat up, cool down, evaporate or condensate process flows. Refinery and Chemical plants can employ hundreds of heat exchangers or condensers in a single process unit, each having its unique process, service and damage mechanism.

Depending on the application, heat exchangers come in all kinds of shapes, dimensions and materials. Construction models most widely used are the so called tube/shell exchangers and fin/fan coolers. Proper working heat exchangers are of major importance for cost effective operation of a plant. Failing or leaking heat exchangers can lead to lower efficiency, unplanned shutdowns or even accidents which in turn can result in damage to equipment, environment or people. During operation, heat exchangers are susceptible to several degradation mechanisms that might eventually result in leakages. Depending on construction, Heat exchanger tubing is subjected to process chemistry on both sides (I.D. & O.D.) such as: water, steam, process, or even air. material and operation condition mechanisms like corrosion, erosion, cracking, thinning, pitting, vibration, impingement or a combination of those mentioned can deteriorate construction materials.

Frequent inspection of heat exchangers is required to:

• detect and respond in time to active degradation mechanisms.
• reduce the chance of unscheduled downtime lost revenue (Reliability).
• ensure environment protection.
• ensure safety of workers.
• determine Corrosion Rate/Remaining Life & Calculate Trending which help in predictive maintenance.
• Provide data for prevention of future failures (failure analysis).
• Hydro-Test is not sufficient. Bore-scope inspection can be misleading and is limited to visual examination.

Likewise, the choice of the available Non Destructive Test technique is of high importance. In general there are two main locations where leakages will occur in a heat exchanger:

• At the tube / tube sheet joints
• Along the length of the tubes

Tube/ tube sheet joints can be visually inspected and standard NDT techniques, like Penetrant Testing or Magnetic Testing can be utilized. Inspection of the entire length of heat exchanger tubes however brings along a few extra challenges. Besides remote visual inspection a range of heat exchanger tube inspection techniques is available. Because the big variety of materials being used for heat exchanger tubes and the various degradation mechanisms that can occur, it’s not possible to use a single inspection technique for all situations. Selection of the right technique(s) for each situation is essential for good inspection results. Widely applied techniques are:

• Eddy current testing (ECT)
• Eddy current array (ECA)
• Tangential eddy current array (TECA)
• Partial saturation eddy current (PSEC)
• Remote-field testing (RFT)
• Near-field testing (NFT)
• Near-field array (NFA)
• Magnetic flux leakage (MFL)
• Internal rotating inspection system (IRIS) ultrasonic testing

Selection of the right technique depends on tube material, expected defect types and the purpose of the inspection. Often more than one technique will be applied to increase the level of confidence of an inspection.