Heat Exchanger Tubular Inspection

This paper covers most of the common (and some not so common) types of NDE methods for heat exchanger (HX) tubular in-service inspections. In addition to noting some of the various advantages and limitations with these methods, the paper covers heat exchanger tubular inspection planning, data analysis needs, a consequence rating method for scheduling inspection and bundle renewals, tubular cleaning methods and tubular inspection technician qualifications. This paper was also published in the proceedings of the ASME PVP 2008 conference.

HX Tubular Inspection Planning

As with the inspection of all other pressure equipment, inspection planning is key to successful inspection and maintenance of heat exchanger tubulars. Planning starts with establishing what data you need from your HX inspection and what you will do with it (covered next). Knowing that information, along with whether the tubes are ferromagnetic or non-ferromagnetic, helps to pick the most appropriate NDE technique (covered later). Planning also involves scheduling the frequency of bundle inspections and repairs (tube plugging, partial or fully retubing or bundle replacement) based on the impact of potential tube failure (covered later). One must also establish the scope and inspection effectiveness required during the examination. Once a tubular NDE technique is established, one must then determine the method and degree of tubular cleanliness that must be achieved (covered later). And finally, the right type and amount of follow-up QC needs to be planned during the conduct of the inspection.

HX Tubular Data Analysis

How one plans to use the data generated from tubular NDE has much to do with what technique one should select. If for instance, one is looking simply for qualitative descriptions of how thin the tubulars are getting, one might choose a more qualitative screening method of inspection like remote field eddy current (RFEC) or magnetic flux leakage (MFL). If on the other hand, one is looking to conduct calculations for reasonably accurate corrosion rates and remaining life, then one might choose a more quantitative method like the Internal Rotating Inspection System (IRIS).