The following describes some of our projects:

Control of Turbine Disc Cracking
Stress corrosion cracking can ocurr on low pressure (LP) turbine disks which operate at or near saturated steam conditions. Though a majority of LP steam turbine disc cracks have been found in keyways, cracking may also ocurr in the disc bore, and on the sides of the disc. Reducing tensile stresses at the surface of the disc will provide protection against the initiation of stress corrosion cracking. O'Donnell evaluated the feasability of various processes for introducing residual compressive stresses at the surface of the turbine disc. Large compressive surface stresses, obtained by plastic prestraining of the material, super-imposed on the operating stresses reduces the resulting surface stresses below the stress corrosion threshold. Several methods for introducing high residual compressive surface stresses in the disc were analyzed. These included overspeeding, bore pressurization, and thermal quenching. Elastic analyses were performed to determine the operating stresess due to shrinkfit, blade load and angular rotation. An elastic-plastic analysis was also performed to establish the residual stresses resulting from the processes used to develop compressive surface stresses. The results were superimposed and the combined stresses evaluated to detrmine the most beneficial process. All three processes generate compressive residual stresses in the bore. Pressurization and overspeeding both can introduce large compressive stresses in the bore, hence they are useful for disc designs where stress corrosion cracking is limited to the bore region. Quenching generates a uniform surface layer of compressive stressses over the entire disc surface. Thus, it can reduce the high operating tensile stresses in stress concentration areas and produce a more favorable operating stress field over the entire disc, including the rim region. O'Donnell performed finite element studies on discs subjected to spray quenching, and developed methods for fabricating crack-resistant discs.

Pump Seals
For a major utility, O'Donnell provided engineering analyses of replacement Reactor Coolant Pump seals. In addition, a thermal hydraulic analysis was performed, providing thermal history curve for each seal, including a detailed analysis of thermal changes in the seals during a loss of cooling water incident.

Control Rod Guide Tube Support Pin Analysis
Cracking and failure of Control Rod Guide Tube (CCRGT) Support Pins (Split Pins) was encountered at a number of pressurized water reactors. The failures in this highly stressed location have been attributed to stress corrosion cracking (SCC). Prior efforts to resolve this issue included improvements in the heat treatment and in the pin geometry. However, these changes did not significantly reduce the stress levels to prevent stress corrosion attack. O'Donnell performed studies to establish design improvements to reduce possbilities of failures. Extensive finite element analyses were performed in which the split pin was subjected to preload, bending and thermal shock loading conditions. Since the stresses were high and the water contains sufficient oxygen to initiate the SCC mechanism, various methods were sought to generate an initial compressive stress on the surface at the neck of the split pin (most highly stressed area). The results confirmed the feasability of quenching to induce compressive stresses in this location.

Incinerator Recuperator Repair
An incinerator recuperator in a chemical plant developed severe leakage due to cracks through the ligaments of the tubesheets. O'Donnell determined that severe differential thermal expansion between the heavy steel frame, which provided peripheral restraint, and the perforated tube sheet had caused tearing of the numerous tube sheet ligaments. Analysis confirmed that the initial failure of a single ligament had caused almost instantaneous progression of the failure through rows of ligaments. A design for temporary repair of the failed unit was provided, consisting of inserting and rolling sleeves in the ends of the existing tubes where the tubesheet ligaments had cracked. These inserted sleeves were then seal welded to the original tubes and a stainless steel pad was applied to the tubesheet to both seal the cracked ligaments and strengthen the tubsheet for temporary operation.

Failure Analysis of a Control Valve Piping Loop
During the startup of a desulferizer at an oil refinery, piping failed in a control loop resulting in a fire that caused considerable damage. O'Donnell performed hydraulic and vibration analyses of the control valve piping loop, and determined that fatigue failure had ocurred due to loop vibration by turbulent flow through the control valve. It was also determined that additional lateral bracing would prevent future failures.

Steam Generator Tubing Wear
O'Donnell performed an independent analysis of wear in the San Onofre Units 2 & 3 steam generator tubes. The results showed that the wear was caused by turbulent flow-induced vibrations of the tubes and batwings which produced forces and relative motions between the batwings and tubes. The variation of wear over the tube bundle pattern was analyzed using finite element methods, which included the interactions between the batwings and multiple tubes. Differences in natural frequencies, in two-phase flow velocities and densities and and in tube and batwing mode shapes stiffnesses produced a very definite pattern of theoretical wear distribution among the tubes which corresponds to the measured wear pattern. Subsequently, conservative tube plugging and staking criteria were developed to provide assurance that no unplugged tube would approach sixty four percent tube wall wear at the end of the second cycle of operation.

Design of Polypropylene Pressure Vessels
O'Donnell designed a number of polypropylene pressure vessels, three to six feet in diameter, and up to forty-two feet long used to hold corrosive liquids. The material has an extremely low modulus of elasticity and creeps at low stress, even at room temperature. Therefore, special design rules had to be devised for the material, and practical allowable stress limits were obtained. In addition, simple reinforcement designs were made to keep stresses at low levels.

Design & Analysis of a Hot Isostatic Press (HIP)
O'Donnell performed the design and analysis of a HIP system of an unusual size for the high pressures involved. It had a thirty-six inch bore, a fifteen foot heated working length, a design pressure of 22,00 psi and a design life goal of 10,000 operational pressure and temperature cycles. O'Donnell designed a ring-and-liner design, carefully considering the local stresses ocurring at the junctures between the adjacent rings. In addition, a seismic analysis was performed on the entire system.

Analysis of Catalytic Reactors
O'Donnell performed analyses on several large catalytic reactors. These reactors were shell and tube heat exchangers, about twelve feet in diameter and thirty feet long. Built with fixed tubesheets, they suffered large discontinuity forces at the tubesheet-to-shell juncture. Very close spacing of the catalyst tubes was required, making the tubesheets relatively sensitive to the discontinuity forces, necessitating inelastic analysis of ligaments of very low efficiency. The tubesheets needed support from the tubes in order to maintain structural integrity. Hence, nonlinear, large displacement analysis of the tube bundle in compression was also required. Lateral displacement of the tubes and the flexibility of the axial and radial support were included in the analysis. Using the results of these analyses, the region of the tubesheet-to-shell juncture was modified to bring stresses to acceptable levels. Because of the loads transmitted between the tubes and the tubesheet, the integrity of the tube- to-tubesheet joints was of particular concern, and inelastic analysis was performed to optimize tube expansion.

Evaluation of Valve Discharge Piping Subsystem
O'Donnell performed an evaluation of a pressurizer safety and relief valve discharge piping subsystem for a slug flow condition event per NUREG-0737. The evaluation addressed the worse case transient (faulted) condition for the Zion Nuclear Facility Pressurized Water Reactor. The evaluation was based on a nonlinear inelastic analysis of the postulated slug flow event for the faulted condition per the requirements of Appendix F of the ASME Boiler & Pressure Vessel Code and the allowables related to the load capacities, maximum displacements, and maximum plastic strains. The evaluation concluded that the piping system could withstand the event. It was then established that rerouting the horizontal header piping was not necessary, resulting in considerable savings to the utility.

Dynamic Analysis of Equipment
For a heavy steel manufacturer of structures, processing equipment and pressure vessels, O'Donnell performed stress and heat transfer analysis of an Isolation Gate for the Dump Heat Exchanger (DHX) for the Fast Flux Test Facility. The gate was analyzed for specific combinations of tornado and seismic transients, internal pressure, vibration, deadweight, and external loads in both open and closed positions.

Analysis of Ruptured Bellows
An engineer was seriously burned when a thirty-nine inch expansion joint in an oil refinery ruptured while workman were performing routine repairs. The ruptured bellows spilled hot catalyst from a fluidized catalytic cracking unit. O'Donnell was retained to establish why the bellows failed. The bellows was a multi-ply design, manufactured in Europe, and assembled to the endrings in the U.S. Although most of the evidence was missing, small peices were available, which were examined. Metallurgical results showed that the stainless steel had become susceptible to stress corrosion cracking, which only could have ocurred through erroneous steel processing, or the bellows being exposed to high temperature. Further investigation found that the assembler had welded the end rings and related hardware to the bellows itself, then subsequently heat treated the assembly, holding in the sensitization temperature. As a result, O'Donnell was able to protect the processing company from liability.

Requalification of Existing Piping
O'Donnell analyzed piping and supports for safety-related piping in various parts of five separate power plants. The adequacy of the piping and supports had been questioned by the NRC. O'Donnell analyzed the piping, and made design corrections where necessary.

Analysis of Methanol Reactor
O'Donnell Consulting performed the stress analysis on a methanol reactor, which is a one-pass, fixed tubesheet heat exchanger. Heat is generated from a gaseous, catalyst enhanced reaction within the tubes. The heat is transferred to the shell side where steam is generated. The principal loading conditions are the shell side and tude side pressures. Deadweight, differences in temperature and expansion, and fluid flow pressure drop were included in the analysis. In addition, the stability of the tubes suporting the tubesheet and the tube supporting system were evaluated.

Structural Evaluation of Repaired Bi-Metallic Weld
O'Donnell Consulting evaluated the safe operating time and temperature for a repaired bi-metallic joint in a 53" diameter line a Fluid Catalytic Cracker (FCC) at a refinery. A major crack was found in the the original joint after six months of operation. The failure ocurred along the fusion interface between 1.25 Cr- .5 Mo base metal and the Inconel 182 weld metal used to make a transition to the 310 stainless steel shell. After careful analysis, it was found that the mechanism was not due to creep-fatigue, creep-ratchetting, or other common modes of failure in structures operated at elevated temperature. Nor was the cracking the direct result of poor welding practices or procedures. The cracking was determined to have been caused by the combined residual welding stresses and operating stresses. An inelastic analysis of the repair weldment including plasticity and creep was performed for the complete thermal history beginning with welding, followed by cooldown to ambient conditions, reheating to annealing temperature and heat treatment for one hour at 1250 F. The heat treated joint was then cooled again to ambient conditions and heated to the operating temperature of 950 F. Analysis of the residual and operating stresses were then performed.