Request Expert

Expert W. Expert has been involved in finding the causes and fixing thermal stress problems since the mid 1970s. These problems have been related to thick walled boiler components, heat exchangers, fluid beds, and fuel cells as well as high temperature piping and tubing failures. These failures involved both steady state and transient conditions and included nonlinear creep and plasticity effects. The failures were related to fatigue, stress-to-rupture or tensile strength. The analysis was performed using classical as well as finite element procedures. NISA, ALGOR, NASTRAN, and MARC have been used. ASME Section VIII div. 2, B31.1, B31.2, B31.3, BS5500 and API 579 criteria have also been applied. The solution to a failure has been design modifications or a change in operating conditions.

As Consulting Engineer at his eponymous firm from 1992 to present, Expert's work includes piping analysis, water wall analysis, non-linear analysis, elastic finite element analysis, reliability analysis, and generator and end ring evaluation.

A specialist in Combustion Engineering from 1974 to 1992, Expert was responsible for fracture mechanics, classical mechanical design, classical buckling problems, finite element analysis, and finite difference analysis.

Expert has solved a number of different types of buckling problems. He used classical mechanics to solve buckling problems in wide flange shapes used as buckstays. (He notes that buckstays are used in boilers to brace the furnace but have different boundary conditions than the same wide flange shape in a building so the buckling rules in the AISC steel code do not apply.) Using classical equations Expert can explain the failures that occurred and produce a safe design. Buckling problems when members were coped were also examined and redesigned as well as buckling of angles in a failed space frame. Nonlinear problems of the buckling of sheet steel used as seals supporting each other in contact was solved using the nonlinear finite element code “MSC-MARC”. In this case it was solved as a static problem and checked to see when the structure became unstable.

Expert has used applied mechanics to solve problems with rotating equipment. Sometimes these problems can be solved using statics and closed form solutions. In other cases dynamic analysis or more sophisticated solutions and testing are needed. In one case involving bowl mill vibration, the problem was related to the rheology of the bed causing a self-excited vibration problem, and changing the dimensions of the grinding element or disrupting the bed solved the problem. In another case involving end rings on generators, the analysis is straightforward using the finite element technique. However, the procedure to determine the adequacy of the shrink fit for the end ring is easily estimated from closed form solutions.

Expert uses classical structural mechanics on a routine basis and at times it meets the client’s needs better than a finite element analysis. He notes that in the 1980s the power industry was concerned about life extension. A finite element analysis of transient conditions in boiler components under creep and plasticity conditions was generally too costly and too time consuming to produce a practical solution. Using his background of studying failed components, Expert wrote simplified computer software using FORTRAN that would calculate the stress from pressure and thermal transients, including the nonlinear effects of creep and plasticity. This approach has been modified for heat recovery steam generators (HRSGs).

A utility had cracking in their piping. The cracks had some suspicious features. Under further review it was found that other repairs had been performed and the hanger system as well as sections of piping had been repaired or replaced. After some monitoring it was found that the problem was caused by operation. After fixing the cracks and changing the operation on this and other units, the hanger and cracking problems stopped.After a collapse of a space frame made of bolted angles, it was found that torsional buckling was the problem, but the problem was not addressed by the AISC code. Others initiated code changes after the problem was exposed.A procedure was developed to design the high crown seal section of a boiler. The original procedure took three to four weeks. The new procedure is done in days with documentation to support what is done.A structure that is held together by springs but, due to an uneven temperature distribution, expands unevenly was analyzed to give insight to some possible problems and a logical basis to proceed with design changes.Tubes were failing in only days of operation in a fluid bed heat exchanger. When a tube was repaired others would fail. The problem was analyzed, the source of the problem was found and a redesign made. The redesign had to allow for thermal expansion, the fatigue load and work in the same size box as the original design. After the redesign the units have worked for years.