ORGANIZATION OF THE ASME BOILER & PRESSURE VESSEL CODE FROM A MATERIALS STANDPOINT
The “heart” of the Guidebook to ASME Section II - Materials Index is the tabulation of ferrous and nonferrous materials specifications by Code section use. However, this Index is only part of the story with respect to Section II and Code materials in general. The focus of this guide is also on how Section II relates to the rest of the ASME Boiler and Pressure Vessel Code, how Section II - Part D is organized, and on some of the common metallurgical issues and terms encountered in the specifications conveyed in Section II,Parts A and B. The word Code in this guide refers to the ASME Boiler and Pressure Vessel Code (see General Overview of the Code for a list of the Code Sections.) Construction book committees refers to SC I, SC III, SC IV,SC VIII, and SC X (where SC is the abbreviation for Subcommittee). Service book committees refers to SC II, SC V, and SC IX who provide service to all construction book committees. All of these Subcommittees are responsible for Code books (or Code Sections) covering the specific subject areas. Scope Section II is an integral part of the 11 section ASME Boiler and Pressure Vessel Code, hereafter referred to simply as the Code. This chapter focuses on how Section II interacts with the rest of the Code, and other related Codes. Important features common to all or most Code sections are discussed. Presentations focus on the “materials person” who should be an integral part of any engineering task. This materials person may be an experienced metallurgical or materials engineer whose role is to provide expert guidance on materials issues, or it may simply be an engineer of another discipline who assumes the broader role of a materials specialist, along with his/her other areas of expertise. The current trends within industry, and practice of engineering in particular,have underscored the need to broaden the skill base and become even more versatile. This Materials Index is evolving with this trend in mind. A Brief History of the Code A series of tragedies in the late 1800s and early 1900s precipitated what would become the first set of steam boiler construction rules. During a 14 year period between 1889 and 1903, approximately 1,200 people were killed in 1,600 boiler explosions in the United States. First recognizing a way to halt this tragic loss of life was the Commonwealth of Massachusetts. In 1907, it enacted the first set of steam boiler construction rules, all of which were conveyed in just three pages. Four years later in 1911, New York and Ohio published similar boiler construction laws. By 1920,nine other states had followed suit. Each state had developed slightly different rules, however. For a manufacturer who desired to market a standard boiler in all states, this presented a severe hardship. Recognizing this unfavorable situation in 1911, the American Society for Mechanical Engineers Council appointed a committee to formulate standard specifications for the construction of steam boilers and other pressure vessels. The Council was also concerned about the care of boilers in service. The first published version of the ASME Code appeared in 1914, covering power and heating boilers. By 1937,nine sections had been issued covering procedures for all phases of fabrication, materials selection,maintenance,and inspection of pressure vessels. The late 1940s brought about newer design methods and advances in materials technology. In the early 1950s, the Code committee completed a comprehensive review of stress tables. Later in that decade, demands for higher temperatures and pressures pushed the envelope into the regime where creep considerations became significant. Within a few years, particularly in the case of Grade 321 stainless steel,failures began to appear, indicating a need to reevaluate the bases for setting stresses.These events led to a renewed emphasis on materials testing. An important step was taken in 1966with formation of the Metals Properties Council. This organization worked closely with the Code committee to improve the databases and the analytical processes used to set Code allowable stresses.As the Code takes on a more international “flavor”, a major step was taken in 1998 to reduce the factor on tensile strength used in deriving allowable stresses for Sections I, III (Classes 2 and 3) and VIII –Div.1 vessels. This step aligns the ASME B & PV Code with comparable European codes. The problem of state-specific boiler codes was gradually rectified as states began to adopt the ASME Boiler and Pressure Vessel Code. Today, the Code has been adopted by nearly every state in America and all 10 provinces in Canada ,and is now well on the way to become a truly international Code. A more complete history of the development of rules for construction of boilers appears in a three part article in Power Engineering, Vol. 100, No. 2, February 1996 (pp 15 - 30). These articles provide further insight into the involvement of the American Boiler Manufacturers Association (ABMA), ASME,and the National Board of Boiler and Pressure Vessel Inspectors (NBBI). No attempt will be made to update this page tally for each new addenda-it is shown here to simply illustrate the general magnitude of the Code. This is quite a change from the three page Code that first appeared in 1914! This phenomenal growth has been driven mostly by technological advances in materials, testing, inspection, design and analysis methodology, fabrication, and over pressure protection as well as demands for rules covering new service conditions. Sections II, V, and IX are “service sections” providing rules and guidance for both nonnuclear and nuclear construction. These sections constitute 4,834 pages or 38% of the 12,591 total pages in the Code. Rules for non nuclear components (Sections I,IV, VI, VII, VIII, X, and their Code cases) involve 3,269 pages or 26%. The remainder of the Code covers nuclear construction (Sections III, XI, and Code cases) with a total of 4,488 pages or about 36% of the Code. Section II alone, with 3,831 pages,represents 30%of the entire Code. Constructing a component in accordance with Code rules requires, first, a basic decision on which category of rules apply. General categories are:
-power boilers (fired),
- heating boilers,
- un-fired pressure vessels,- nuclear systems, or
- fiber-reinforced plastic pressure vessels.
One important issue to understand is that each category has unique materials requirements for that type of construction. Within each of the governing Code books are additional factors that must bead dressed as the design, fabrication, testing, inspection, and installation processes progress. The following outlines show the organization of the various Code sections with particular emphasis on materials requirements. These outlines may serve as checklists or quick references for the materials specialist in Code construction.
Section I-Power Boilers Part PG- General Requirements for Power Boilers and High Pressure, High Temperature Water Boilers General Materials
PG-5 General PG-6 Plate PG-7 Forgings PG-8 Castings PG-9 Pipes,Tubes and Pressure Containing Parts PG-10 Material Identified with or Produced to a Specification Not Permitted by This Section, and Material Not Fully Identified
ORGANIZATION AND THE USE OF SECTION II, PART D There is a near-symbiotic association between the “heart” of this article to ASME Section II and Section II, Part D. Each has influenced the other as they progressed to their current forms. The evolution of both spanned a time period of nearly 20 years, which lends support to the adage that “good things take time.” Unfortunately, the publication of Section II, Part D represented a somewhat controversial departure from an older, well established way of conveying allowable stresses and properties of Code materials. Some of the confusion surrounding use of this“new” approach is addressed by this chapter, and many of the questions will be answered and misunderstandings dispelled.
Section II, Part D is now the focal point for allowable stresses and properties for those materials permitted in Section I, III and VIII (Divisions 1 and 2) construction. This chapter delves into the development of Section II, Part D, its organization, use of the many stress and property tables, external pressure charts, associated appendices, and current efforts to adopt non-ASTM (foreign) specifications. It also provides additional useful information on materials behavior. As frequently suggested in Chapter 1, much of this information in Section II, Part D may be valuable in other engineering assignments. So,becoming comfortable with its organization and use is a MUST.
A Brief History of the Development of Section II, Part D
This author wrote a letter on October 5, 1979 to the Chairman of Subcommittee on Properties (as it was called at that time, before it was combined with the Subcommittee on Specifications to become the current Subcommittee on Materials),proposing that there be an “attempt to combine stress tables within a separate Code book.” It was further suggested at that time that other minimum and nominal properties and other materials characteristics, that are independent of Code application, be included as well. The arguments cited were that it would be a “quality control system to ensure consistency” and that it would eliminate a lot of duplicate pages, common to numerous Code sections. This letter also recognized “how this approach could uncover minor (and perhaps major) discrepancies in stress listings.” The gestation period for this idea was about five years, culminating in early 1985 with a move to resurrect a Task Group on Tabulation of Allowable Stresses and Materials Properties. The ambitious goal of publishing a new document in the 1986 Edition of the Code was obviously not met, but the wheels of motion were moving forward.
Michael Gold, current chairman of the Subcommittee on Materials, presented a paper at the 1995 ASME Pressure Vessel and Piping meeting, in Honolulu, Hawaii in June 1995, entitled “Section II, Part D and Adoption of Foreign Materials.” The balance of this historical recap uses portions of Mr. Gold’s paper and is updated to cover the time since that paper was authored. Section II, Part D first appeared in the 1992 Edition of the Code, combining into one book, as suggested earlier, design stress values and materials property values previously published in Sections I, III, and VIII (Divisions 1 and 2). The stated purpose for publishing the information in a single volume for use with the respective sections was to ensure consistency of design values. This was essential since criteria used to develop the values and the data bases upon which values were based were identical.
The first version of Section II, Part D was nothing more than an editorial reformatting of information that existed in the four targeted Code sections. No attempts were made at that time to correct discrepancies that would now be painfully obvious. Over the next three years, concerted efforts were expended to eliminate the many inconsistencies that became evident not only in stress values, but in notes, nomenclature, and use temperatures. Corrections then allowed the merging of many stress lines,and that reduced the size of Section II,Part D.
The 1995 Edition of Section II, Part D was a “slimmed down” version with a new note system, further simplifying the stress tables. Also making the stress tables more user friendly was the numbering of lines to follow stress lines and associated information from one page to the next one, two, or three pages. Efforts will continue to further improve the quality of stresses and material properties as better data become available.
Structure of Section II, Part D
The Michael Gold paper cited earlier also provided an excellent description of the organizational structure of Section II, Part D. This write-up was based on “A Users Guide to BPV Section II Materials, Part D Properties: 1992 Addenda”, written by G. M. Eisenberg, at that time Secretary for the B&PVC Main Committee. The following was taken verbatim from Mr. Gold’s paper, with permission from ASME.
The organization and structure of Section II, Part D, has been described thoroughly by G. M. Eisenberg (1992), in the User Guide to BPV Section II, Materials, Part D Properties: 1992 Edition, which was published as part of the 1992 Addenda update to Section II, Part D. Because that User Guide did not have page numbers, even current users of the Code may have lost track of it by now, so much of the information developed by Eisenberg has also been included here.
Section II, Part D, is divided into Sub parts, followed by Appendices. These are described below.
Sub part 1: Stress Tables Grouping by Criteria
The individual tables in Sub part 1 include values for materials, based on common stress criteria. For materials other than bolting, Tables 1A (Ferrous) and Table 1B (Non-Ferrous) contain maximum allowable stress values, based on the criteria that have been adopted for use in: Section I; Section III, Class 2 and 3; and Section VIII, Division 1. Tables 2A (Ferrous) and 2B (Non-Ferrous) contain design stress intensity values based on the criteria used for Section III, Class 1, and Section VIII, Division 2.
For bolting materials, Table 3 contains allowable stress values based on the criteria used in: Section VIII, Division 1; Section VIII, Division 2, according to the rules of Appendix 3 of Division 2; and Section III, Class 2 and 3. Table 4 contains design stress intensity values for bolting based on the criteria used for: Section VIII, Division 2; according to the rules of Appendices 4, 5, and 6, of Division 2; and those constructed according to the rules of Section III, Class 1. Table U contains tensile strength values for ferrous and nonferrous materials, previously contained only in Section III. Table Y-1 contains the yield strength values for ferrous and nonferrous materials previously contained in Sections I, III, and VIII, Division 2. Table Y-2 contains factors for limiting permanent strain for nickel, high nickel alloys, and high alloy steels from data previously contained in Sections III, and VIII, Division 2. Tables U-2 and Y-3 contain ultimate tensile strength and yield strength values respectively for additional materials used in Section VIII,Division 3 construction.
Ordering of Listing
The sorting order for materials,as they are listed in the tables, differs between Tables 1A and 1B. This difference persists in the other tables, as well, for ferrous and nonferrous materials,respectively. In Tables 1A and 2A,and the portions of Tables 3, 4, U, and Y-1 containing ferrous materials, the underlying sorting sequence in order of priority, is: nominal composition, tensile strength ST, yield strength SY, specification number, and grade or type. Two variables to this ordering are worth mentioning: There is no distinction made among the carbon steels on the basis of nominal compositions shown as C, C-Si, C-Mn, and C-Mn-Si. These were all treated as being identical carbon steels, with regard to nominal compositions, and were placed at the beginning of the table. In fact, those distinctions in Nominal Composition for carbon steels will soon be eliminated from Code stress tables and those materials will all be described simply as “C Steels.” This is already reflected in this version of the Materials Index. Micro-alloyed carbon steels will still retain their original distinction even though the reported thermophysical properties for carbon steels also are appropriate for these micro-alloyed carbon steels. The ordering of the carbon steels in stress tables begins with the tensile strength as the primary discriminator. Further, the austenitic stainless steels, those with chromium contents between 16 and 25,were separated from the ferritic steels and placed after them.
In Tables 1B, 2B, and the portions of Tables 3, 4, U, and Y-1 containing the nonferrous materials, the sorting priority is somewhat different: alloy/UNS number (alpha-numeric), tensile strength ST, yield strength SY, class/condition/temper, and specification number. Nominal compositions are not included as a sorting priority for the nonferrous materials. In fact, nominal compositions are not listed for the aluminum and copper alloys, because of all of the many different variations of nominal compositions available in different systems for these materials. For all nonferrous materials, the primary ordering sequence is based on the more unique UNS numbers that have been assigned to each grade.
Other Information in Tables
In addition to providing columns for the materials and the criteria by which they are sorted, and, of course, the design values, other information is provided in the stress tables: This includes nominal composition (for the other nonferrous materials), product form (e.g. tube, pipe, plate, etc.), specification number, type or grade, alloy designation or UNS number, class/condition/ temper, size/thickness, welding P-number and group number, minimum tensile strength in ksi, minimum yield strength in ksi, and most importantly, the maximum temperature and applicability for each material in the Construction Codes appropriate for each table.
Applicability-Temperature Limit Columns
An example of the applicability / temperature limit column heading,is as follows.
This entry indicates that, for this particular stress line, the values shown are appropriate for use in Section I construction, up to a maximum temperature of 800°F, and are appropriate for use in Section VIII, Division 1 construction, up to a maximum temperature of 1,500°F. The NP entry indicates that this stress line is not permitted for Section III construction. The difference in temperatures of applicability between Section I and Section VIII,may have no technical basis. It is possible that no inquirer ever requested use of this material in Section I construction, above 800°F. Many of these types of inconsistencies have been, and will continue to be eliminated in future Addenda. Further, the NP doesn’t necessarily mean that this particular material would never be permitted in Section III construction; it might mean that either no one has ever requested this material for use in Section III construction, or that there is another stress line, with some differences, that has previously been approved for Section III construction, and it would normally be found immediately above or below this particular line. Subcommittee II is working to eliminate such inconsistencies, and the 1995 Edition went along way in that direction.
External Pressure Charts and Notes
Other information included in the stress tables are the external pressure chart numbers, and their references. Many inconsistencies in the referenced external pressure charts existed in the initial publication of Section II, Part D, but these have since been addressed and resolved.
The 1992 Edition and its three Addenda contained separate tables for notes, essentially as they originally appeared in the construction Codes. The 1995 Edition merged all of those notes into a single set of notes applicable to each stress table. Unfortunately, those who became familiar with a particular identification number for certain notes will have to learn new numbers. The new system is much more understandable and combines many similarly worded notes that had exactly the same meaning into single notes.
Sub part 2: Physical Properties Tables
There are four sets of physical properties tables. Those in the first set are the nominal coefficients of thermal expansion, numbered TE-1 through TE-5. These combined existing values from the 1989 Editions of Section III and Section VIII, Division 2. The five tables cover ferrous materials, aluminum alloys, copper and copper alloys, high nickel alloys, and titanium and titanium alloys, respectively. The next table is Table TCD, which includes nominal coefficients of thermal conductivity and thermal diffusivity.