This past January, Pressure Sciences was awarded a contract for a $60,000 Ben Franklin Challenge Grant to develop software to analyze filament-wound composite pressure vessels.

The Ben Franklin Challenge Grant Program is supported by the Ben Franklin Technology Center of Western Pennsylvania and sponsored by the Commonwealth of Pennsylvania. Pressure Sciences and its partners, CP Industries and ANSYS, Inc., proposed a two-year program to develop the software. Pressure Sciences will lead the vessel modeling and analysis efforts, CP Industries will build and test two prototype vessels that will be designed using the new software, and ANSYS will provide its finite element platform and expert consulting for use in the development effort.

Filament-wound composite vessels are intrinsically lighter than metal vessels, but their strength to weight ratio can be further improved by optimizing the design for a specific application. Performing this optimization requires detailed knowledge of the stresses throughout the vessel. Stress analyses of filament-wound pressure vessels are limited to finite element analysis (FEA) or simplified hand analyses - and FEA is the only method available to obtain detailed local stresses throughout the vessel.

Filament-wound cylindrical pressure vessels are three- dimensional, orthotropic layered structures whose properties and behaviors vary between layers, and in some regions along a layer. A three-dimensional FEA model can be constructed and evaluated. However, developing such a model is almost always impractical for commercial applications because it requires extensive manpower and computer power, and therefore often costs more than building and testing a prototype.

A more practical method for evaluating filament-wound pressure vessels is to use axisymmetric FEA models. A filament- wound pressure vessel is essentially an axisymmetric structure with asymmetric helical layers. Therefore, axisymmetric FEA models can be used to represent the geometry if effective material properties that accurately relate the properties of the laminae to the appropriate location on the vessel can be mapped to the axisymmetric FEA model.

This is the task we have undertaken: we look forward to completing this work, and being able to offer the software and new capabilities to our clients.

With industry awareness of OSHA, EPA, and state DEP regulations heightened, Pressure Sciences has seen increased activity and requests for support for process plant Mechanical Integrity programs. In Pennsylvania, this extends to assistance in implementing DEP rules for registration of aboveground and underground storage tanks.

As experts in the ASME B&PV and B31 Codes and the API standards, we provide the engineering evaluation, reporting, NDE planning and oversight for these safety programs. Deficiencies such as undocumented pressure vessels, excessive general or local corrosion, lack of safety valves, inadequate relief capacity and incorrect relief valve settings are some of the findings that we help clients resolve with minimal plant impact.

A typical project involves conducting a client's Documentation and Inspection (D&I) program, and we are working with several chemical plants in developing D&I packages.

We have developed baseline engineering and inspection data, and provided recommendations for further detailed evaluations of suspected problems. Our engineers work on-site to develop the D&I package, and direct the efforts of an NDE firm in obtaining the visual, wall thickness, and weld ultrasonic or radiographic inspection data required to demonstrate Mechanical Integrity. We provide reports on each piece of equipment, and include the calculation of remaining life and inspection intervals according to appropriate post-construction code requirements. We also professionally certify the results in Pennsylvania, Ohio, Delaware, and other states.

Pressure Sciences has expanded its permanent staff with the addition of three new employees - John Breen, Jim Watson and Doug Fraser - who are all located in our Edgewood Towne Centre offices.

John Breen started in September 1995 as Senior Piping Specialist. He has 35 years experience in design, condition assessment, failure analysis, and remediation of piping systems in refineries, chemical plants, power stations, and NASA test facilities. He has worked extensively with Process Safety Management projects, and received certification in the University of Southern California's PSM program, where he subsequently taught the implementation and execution of Mechanical Integrity programs for process equipment.

John has also worked with the NBIC, the API Standards for Inspection of vessels and tanks (API 510 and 653), and the ANSI/ ASME B31 Codes for pressure piping. In addition, he helped to develop the examinations for the API 570 certified piping inspection program. John is a voting member of the B31 Mechanical Design Committee.

Jim Watson began in March 1996 as Principal Engineer. Jim brings over 35 years of experience to the company. For the past 17 years he had been a Senior Consultant with AEA Technology, where he performed analytical and experimental investigations, with emphasis on component performance, durability, and safety. He has extensive knowledge of materials, fatigue and fracture mechanics, and has conducted numerous analytical and testing programs.

Jim was previously a Senior Engineer at Westinghouse, where he performed structural analyses of a wide range of components. He was also an instructor in the Mechanical Engineering Department at Tennessee Technological University, and originally worked for the U.S. Naval Ordnance Laboratory in design, analysis, testing, and research for electro-mechanical components.

Doug Fraser has been appointed Manager of Business Development. He has 23 years experience in engineering business development, project management, and site engineering. His background includes quality and inspection services, cogeneration and gas turbine engineering and marketing, and piping and structural analysis. He has also had involvement in OSHA Mechanical Integrity programs.

Doug previously worked at Davy International's QA/QC Services group, Polo/TCI Consultants, Ensys, and Westinghouse (both Power Generation and Nuclear Energy). For Westinghouse, he was the Midwest Technical Center Manager (Schaumburg, IL), site engineering manager at several nuclear construction projects, turbine engineering and marketing support manager in Orlando, and senior engineer / analyst in Monroeville.

In this column, we describe significant recent and near-term releases by the ASME Boiler and Pressure Vessel Code committees, mostly regarding Section VIII. Remember that rules approved by the Main Committee in May are issued in the Addendum dated December 31 and are mandatory the following July 1. Also remember that anything that is not stated as an accomplished fact is subject to change. We cannot speak for ASME.

After almost twenty years of work, Section VIII, Division 3, Alternative Rules for Construction of High Pressure Vessels, is nearing release. It has been voted by the Main Committee in June. The new Division will provide rules for high pressure vessels that were previously treated as "State Specials" in the various jurisdictions.

After a somewhat shorter period of development, new rules for bolted flange joints, that account for leak-tightness as well as strength in the design, are approaching readiness in the Special Working Group responsible for their preparation. New rules that assign various grades of carbon steel (SA-216) and low alloy steel (SA-217) castings to impact test exemption curves in Section VIII, Division 1 have been approved by the Main Committee, and updated toughness rules for carbon, low alloy, and high alloy steels that are similar to those in Division 1 are being prepared for Division 2.

Finally, the Subgroup on Design has been considering revised rules for the design of formed heads and new rules for external pressure for many years, and although it's just my opinion, I believe these new rules will be completed in the near future.

PSI's John Breen recently spent 3 months in Texas working for the City of Austin (on D'Appolonia's service contract) in assessing the condition of high energy piping (HEP) systems at the Decker Creek Station, Unit 2 (425 MWe, gas fired). He also provided on-site outage support for distressed systems repair. This had occurred as a result of undersized hangers and an upset-prone, floating support system design with few rigid hangers, and failures of constant force hangers. The HEP assessment included hanger functionality walkdowns, recording piping movements and relative elevations, and measurement of piping wall and insulation thicknesses. These were used to reestablish the basis for stress and weight analyses, to plan the inspection of the boiler header supports for damage, and to identify conditions with potentially immediate adverse consequences to structural integrity.

While on site, John was also able to help reset hangers to temporarily restore the hot-cold range of movements to prevent load transfer to the boiler and turbine. He performed simplified analyses for various scenarios for design remedies to obtain data for procuring new hangers, and to reset the existing hangers. John previously helped the remediation of Decker Creek Unit 1 piping systems that had been distressed by differential settlement of the building and turbine foundations, and consulted on the replacement of the Hot Reheat System piping.

Union Carbide recently engaged PSI to evaluate the large diameter reaction gas recycle piping system for one of their licensee's plants. The need for this evaluation was prompted by the very high seismicity in the region. Our work included evaluation of soil conditions and development of soil-springs for soil-structure interaction analysis, and for input to the Triflex® computer model. Based on the zero period ground acceleration (ZPA) of 0.29 g's, horizontal and vertical response spectra were developed for the dynamic seismic analysis. Parametric studies were performed to assess the sensitivity of the results to calculated soil-spring stiffness to ensure that high calculated stresses were, in fact, a result of piping system design. Finally, recommendations were provided for modifications (including a redesign of the pipe supports) that would alleviate excessive pipe stresses and loads on rotating equipment.

News from Pressure Sciences is a periodic newsletter focusing on the activities of Pressure Sciences, Inc.

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Pressure Sciences, Inc.
1789 S. Braddock Avenue
Suite 290
Pittsburgh, PA 15218

Phone: (412) 371-3117
Fax (412) 371-0424
email: info@press-sci.com

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