In 1989, Pressure Sciences was retained by a piping contractor who had installed ASTM A312 Schedule 10 seam welded Type 304L piping at an air force base. As part of a jet fueling system, the piping was installed under runway concrete. Subsequently, the longitudinal weld seam in a portion of the pipe ruptured, causing significant leakage. Similar failures occurred later at a number of other air force bases.

Dr. Selz examined the failure surfaces and concluded that cyclic loading had caused pre-existing flaws (lack of fusion) in the weld seam to propagate through-wall. The government denied that the piping was exposed to cyclic loading, and in addition claimed that the areas of partial lack of weld fusion violated the wall thickness requirement of the A312 specification.

In 1996, this matter came to trial in the U.S. Court of Federal Claims. Dr. Selz testified for the contractor that wall thickness was a different characteristic than lack of weld fusion, and that the fuel valves protecting the airplanes from overpressurization had, in fact, caused repeated hydraulic transients in the piping when actuated. These hydraulic transients were the principal source of the cyclic loading that caused the pre-existing flaws to propagate through the pipe wall.

In 1998 the Court, quoting extensively from Dr. Selz?s "convincingly and carefully articulated" testimony, found in favor of the contractor in all material issues.

Pressure Sciences recently completed several design/build contracts for special purpose stainless steel, high pressure vessels for use in the electronics industry. The vessels were designed for quick access, infinite pressure cycles, and fail-safe operation. We developed a 100% machined system with a two piece closure assembly and O-ring sealing. This approach prevents a potential accident by allowing leakage, which prevents pressure buildup if there is incomplete head closure. The two-piece closure also addressed the client’s need to minimize operator lifting loads due to OSHA concerns. With the separate retaining ring and hemispherical head, the maximum operator lifting load was reduced to under 15 pounds.

Harliss Specialties (Irwin, PA) reviewed the design, Code calculations, and drawings for conformance to Section VIII, Division 1; subcontracted the precision machining to Gentile Manufacturing (Leechburg, PA); performed hydrotesting; and applied the U-stamp. The system, shown below, was delivered six weeks after client release!
 
 

Pressure Sciences was awarded a contract to provide pressure vessel design assistance to a major manufacturer of equipment to the hydrocarbon process industry. This client had won a large award and had developed a substantial overload in its in-house engineering department. In order to meet production schedules, Pressure Sciences assisted in performing the ASME Section VIII, Division 1 design certification analyses for two vessels making up a 

large distillation column. We also confirmed the design integrity of various platforms, the anchorage, and the flare stack.

Jim Watson led the project, using the COMPRESS^® program as the principal analysis tool. He determined that some of the initial design details conflicted with ASME B&PV Code requirements, and was able to specify changes to qualify the equipment – items such as increasing thickness of reinforcing pads for nozzles, and resolving closely spaced nozzle openings and pad / ring interferences.

This column also uses large tangential nozzles for mixing, and, since such nozzles cannot be evaluated with the WRC-107 methods in COMPRESS^®, additional work was authorized for finite element analysis (FEA). We used ANSYS^® to calculate stresses, evaluate reinforcement pads and gussets, assess nozzle loads, and document code compliance.

Decker Creek Piping Remediation

John Breen has worked with the Decker Creek Power Station (Austin, Texas) staff for much of the past year in providing technical assistance for their Unit 2 high energy piping remediation program. The critical systems – Main Steam, Hot and Cold Reheat, Extraction Steam, and Boiler Feedwater – have experienced physical changes over time that have resulted in bottomed-out hangers, loss of thermal travel, increased nozzle loadings on the turbines and boilers, and weakened hangers due to accumulated exposure to the environment.

To restore intended pipe movements, properly support system weight, and reduce nozzle loads, it was necessary to analyze the system for actual weights and thermal loads. To accomplish this, John performed B31.1 piping analyses with the CAESAR II^® program using actual spool piece, valve, and insulation weights. He then imposed actual measured displacements in both hot and
 

cold positions to drive the system. In this way, John developed accurate pipe stresses and hanger loads, and specified the changes needed to improve system performance. This effort will help to ensure the longest possible useful life. John also continues to provide station outage support.

Elevated Temperature Vessel
Qualification

Pressure Sciences recently assisted a manufacturer in determining the useful life of a high temperature catalyst collector subjected to large thermal cycles that operated in a regime where creep and relaxation effects are significant. Analyses of the Section VIII, Division 1 vessel were performed using the criteria of Section III, Subsection NH, "Class 1 Components in Elevated Temperature Service." This new subsection incorporates previous Code Case N-47 rules. The analyses included the effects of time dependent material properties and the corresponding structural response. Failure modes not considered by elastic analysis techniques – ductile rupture, creep rupture, creep fatigue, incremental collapse and ratcheting, and creep buckling, were also assessed.

We are pleased to announce that Mr. Clayton F. Heberling, P.E., has joined the staff of Pressure Sciences as of March 1, 1998. Clay brings a wide 
range of experience to the company and is an expert in finite element modeling and analysis.

His initial projects include leading the design qualification effort for transport tanks per Section VIII, Division 2 for a tank manufacturer, a fracture mechanics and critical flaw size analysis of a high temperature nickel alloy vessel, and Phase 2 of a crash worthiness study of MC-331 cargo tanks for the U.S. DOT.

Clay has substantial experience as a user and trainer of FEA techniques for structural, dynamic, heat transfer, fluid flow and nonlinear analyses. He has also worked with many CAD packages, including ProEngineer. Before his association with Pressure Sciences, Clay was with Algor as an applications engineer and instructor; with Paul Rizzo Associates where he performed a variety of seismic qualification and civil engineering projects; and with Westinghouse Advanced Energy Systems where he performed ASME Section III and VIII stress analyses, designed wind turbines, and designed pressure vessels and piping for a phosphoric acid fuel cell facility.
 

 Clay may be contacted via email at clayh@press-sci.com

Allen Selz was elected Fellow of the ASME in November 1997. Allen’s career spans 45 years, and he has devoted substantial effort to the advancement of the ASME.  He was appointed to the Main Committee of the ASME B&PV Code in 1991, currently chairs Subcommittee XII, Transport Tanks, and sits on many other committees.

A manufacturer of pressure vessels and heat exchangers retained Pressure Sciences to perform design analyses for a flue gas cooler being supplied to a refinery. Because of the high temperatures and large number of thermal cycles, this equipment was designed with a flexible tubesheet and ceramic insulation. The tubesheet thickness and tubesheet-to-shell juncture were the most critical stress locations, and sophisticated modeling and analysis were required to accurately determine the stresses. A portion of one of the models is shown to the right.

The heat exchanger was built to the requirements of ASME Section VIII, Division 1. However, because of the cyclic service and unusual geometry, the design-by-analysis approach of Division 2 was utilized to qualify the components.