Eddy Current’s Role in the Inspection of Welded Structures
by J. Hansen
Weld inspections are carried out both during fabrication and during the operating life of welded structures. A number of techniques are used, and some are prescribed by regulatory authorities in preference to others. For example, X ray has long been the authorized technique for providing volumetric inspection of welds during manufacture in the oil sector, both in the fabrication yard and on the lay barge. X ray is written into all the approved procedures. However, new techniques such as automated ultrasonics and digital radiography are now also gaining acceptance and approval and are providing manufacturers with a greater choice and flexibility.

Inspection Program for a Light Rail Bridge
by G. Gardner
A recent challenge for Stinger Welding, Coolidge, Ariz., was fabrication of a steel tube-structure bridge to link the Phoenix, Ariz., light rail network with the east-valley communities across Tempe Town Lake (a section of the normally dry Salt River contained by upstream and downstream inflatable dams) — Fig. 1.
   
The cyclically loaded truss bridge has two parallel spans between the north and south abutments (to bear both north-  and southbound tracks), and is supported in midspan by nine Y-shaped concrete piers. Tubular cross-diaphragms, located at both abutments and at the nine piers, interconnect the parallel trusses — Fig. 2. Disc bearings, two on each abutment and two atop each pier, control bridge movement. A concrete deck will be poured on stay-in-place decking. Details of the project are outlined in Table 1.

Advances in Eddy Current Inspection of Tube
and Shell Heat Exchangers
by D. DeVries et al.
Eddy current testing (ECT) is a proven, reliable technique for the inspection of heat exchanger tubing. One of four techniques that comprise the electromagnetic test (ET) method, the ECT technique involves passing an eddy current probe through a tube in a heat exchanger bundle. The AC-driven probe creates a varying electromagnetic field around itself that interacts with the tube wall. Eddy currents generated in the tube wall travel in well-defined paths and at specific depths within the tube wall until they encounter changes such as cracks or corrosion in the material that they move across — Fig. 1.

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