George Miller

ASME Pressure Vessel Internals and Their Design Code

It is common for designers to use the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME) when designing vessel internals (i.e. process trays, bed supports, bolted connections, etc). Typically the ASME allowables are directly applied to internals without any regard to the member geometry or failure modes. The ASME code was developed for modes of failures experienced in the pressure boundary and was not intended to be utilized for the design of structural components. ANSI/AISC 360-10 “Specification for Structural Steel Buildings” (AISC) addresses the failure mechanisms experienced in structures based on their geometry and boundary conditions. This paper will provide several examples along with a direct comparison between structural members designed to the AISC and ASME codes. This paper will also provide guidance for using the AISC methodology with material properties at design temperature from ASME Section II Part D for robust design of internal structures.Copyright

Use of Laser Measurement Systems for Out-of-Roundness Check of ASME BVP Section VIII Div.1 Pressure Vessels

Since the 1956 Edition of the ASME Boiler and Pressure Vessel Code Section VIII (ASME B&PV Code) [1], the Out-of-Roundness of circular sections of pressure vessels subject to external pressure have been inspected using a segmental template per paragraph UG-80(b)(2). Newly approved ASME Code Case 2789 “Laser Measurement for Out-of-Roundness Section VIII, Division 1” to the ASME B&PV Code expands the out of roundness checking to allow the use of laser measurement systems. Today with large vessels approaching 60 feet (18.2 m) in diameter, laser measuring systems allow an expeditious and cost effective method of inspection for out-of-roundness.The Code Case allows the fabricator to use measurements obtained from laser measuring to either verify the vessel in the arc segments or the entire vessel circumference is held to a circularity tolerance. The second option is similar to the requirements of European Standard EN 13445 (EN 13445) [2] which uses circularity.This paper will explore the origin and objective of the template and presents how laser measuring systems make use of the latest technology available to check for out-of-roundness. The paper will address laser measuring systems, procedures for taking measurements, and processing of the data into a format that can be verified by Authorized Inspectors.Copyright

Case Studies in Local Heat Treatment of Pressure Vessels Applying WRC-452 Principles

The Welding Research Council (WRC) Bulletin 452 titled “Recommended Practices for Local Heating of Welds In Pressure Vessels”(1) was first published in June 2000. This document considers various issues associated with the local heating of welds in pressure vessels and addresses the application of controlled heat in the weld metal, heat affected zone (HAZ) and a limited volume of base metal around the weld.ASME Boiler and Pressure Vessel Code Section VIII Division 1, paragraphs UW-40, (a) 3 and 8 require that post weld heat treatment (PWHT) be carried out in a manner such that the thermal gradients are not harmful. WRC Bulletin 452 provides guidelines for local PWHT to satisfy this requirement.This paper provides examples of local PWHT (if not heated as a whole vessel in a furnace) based upon utilizing a soak band and calculated heated band and gradient band widths based upon WRC 452 recommendations. The paper addresses both circumferential and spot PWHTs and demonstrates that the guidelines provided in WRC 452 can also be used as a starting point for determining the band widths for spot PWHT.Copyright

Comparison of Pressure Vessel Codes ASME Section VIII and EN13445

This paper consists of a comparative study of the primary technical, commercial, and usage differences between the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section VIII and the European Pressure Vessel Code EN13445 (EN). This study includes a review of “Comparative Study on Pressure Equipment Standards” (hereby referenced by the “EC Study”) [see REF-1] and provides technical comparisons between the code design requirements, material properties, fabrication, and contributing effects on overall cost. This study is intended to provide a broad viewpoint on the major differences and factors to consider when choosing the most appropriate vessel design code to use.Copyright

The Use of Vanadium Modified Materials for Reactor Fabrication

Vanadium modified 2 1/4Cr-1Mo and 3Cr-1Mo alloys used for the fabrication of hydroprocessing reactors offer a number of important advantages over the corresponding conventional alloys. These include increased resistance to hydrogen attack, a lower susceptibility to temper embrittlement, increased resistance to weld overlay disbonding and higher strength resulting in thinner and lighter reactors. Since the first vanadium modified 3Cr-1Mo reactors first went into service in the early 1990’s, vanadium modified alloys have gained acceptance and today more than one hundred and forty vanadium modified reactors and pressure vessels have been placed in service and are operating in severe process environments. Despite the excellent benefits of these materials, they also exhibit less desirable characteristics such as reduced weldability, higher hardnesses in the base metal, weld metal and heat affected zones and the need for higher post weld heat treatment (PWHT) temperatures. Additionally, these materials have a reduced notch toughness at lower temperatures especially in the as welded condition and require intermediate stress relieving (ISR) in lieu of dehydrogenation treatment (DHT) in restrained and highly stressed joints such as nozzle to shell and head welds. These materials also require extra care and effort to be taken during fabrication. The paper presents a serious weld metal cracking problem that occurred with vanadium modified materials during the installation of a nozzle in a restrained and highly stressed weld when only DHT was performed instead of the more beneficial ISR. This fabrication problem is provided as a typical example of problems that can occur during fabrication with vanadium modified materials, and points out that additional care must be taken during fabrication when using these materials. The paper identifies the main causes for the cracking using information based upon mechanical, metallurgical and stress analyses and suggests steps that may be taken to circumvent similar reoccurrences.© 2005 ASME

Transient Thermal Finite Element Analysis Based on Field Measured Data and the Impact on Fatigue

Many vessels experience significant thermal loads in operation. This paper discusses a method used to develop the internal thermal boundary conditions (film coefficients) required to evaluate thermal loads when the thermal properties of the internal fluid are unknown. In a thermal analysis it is critical to determine the correct film coefficients to achieve the proper behavior. Improperly quantified heat up rates can have a dramatic effect on the overall design. An example is provided to show how assumptions on thermal input can directly effect the results. The method described in this paper uses Finite Element Analysis (FEA) to determine internal film coefficients based on field measured thermocouple data.© 2004 ASME