Introduction to ASME B31J Standard
1. What is “ASME B31J Standard”
There are many diverse shapes of pipe fitting components, such as bends or tee connections. In comparison with run pipe, fittings have more or less flexibility depending on shape and discontinuity, and thus, stress level on fittings is different from stress on run pipe even under same amount of load and pressure. To take into consideration of this effect in beam type analysis modeling, stress intensification factors (SIFs) and flexibility factors(k-factors) have been introduced.
The American Society of Mechanical Engineers (ASME) B31 Code books, such as ASME B31.1 or ASMEB31.3, provides stress intensification factors (SIFs) for various standard fittings and joints. These are based upon work carried out in the mid 1900’s by A.R.C. Markl, a pioneer in the field. However, ASME B31 Code does not provide guidance on how existing SIFs were developed, or how to establish SIFs for standard fittings and joints not in the current tables, or for nonstandard fittings or joints.
To satisfy a desire for a standard method to develop stress intensification factors for ASME piping components and joint, the ASME B31 Code for Pressure Piping Technical Committee on Mechanical Design(MDC) released ASME B31J Standard, which provides a uniform approach to the development of SIFs for standard, nonstandard, and proprietary piping components and joints of all types.
2. What is update (from “ASME B31J-2008” to “ASME B31J-2017”)
ASMEB31J-2008 provided only a standard test method for establishing SIFs. In contrast, ASME B31J-2017 provides an update to the calculations of flexibility factors, Sustained Stress Indices, and SIFs for specific types of piping components and geometries. These updated formulas and tables facilitate engineering designs without first requiring an experiment or test to be conducted for every each fitting.
Table 2‑1. ASME B31J-2008 vs ASME B31J-2017
| ASME B31J-2008 | ASME B31J-2017 | |
| Title | Standard Test Method for Determining Stress Intensification Factors (i-Factors) for Metallic Piping Components | Stress Intensification Factors (i-Factor), Flexibility Factors (k-Factors), and Their Determination for Metallic Piping Components |
| Contents | ||
| SIF Table | X | O |
| Flexibility Table | X | O |
| SIF Test Procedure | O | Nonmandatory Appendices A |
| Test Method for Branch Flexibility Factor | X | Nonmandatory Appendices B |
| Use of Branch Flexibility Factor | X | Nonmandatory Appendices C |
| Sustained Load Test Procedure | X | Nonmandatory Appendices D |
3. What is the difference (ASME B31.1 Appendix D, ASME B31.3 Appendix D and ASME B31J-2017)
Although the ASME B31.1 Code and B31.3 Code have provided k-factors and SIFs in Appendix D, there are some limitations in the accuracy and adequacy of these formulas.
The ASME Committee realized that SIFs and k-factors in the various B31 Code books were not consistent or up to date. So ASME initiated a research project completed by the MDC to incorporate recent research and current manufacturing practices in the SIF and k-factor test procedures. These now provide a consistent and up-to-date table of SIFs and k-factors for metallic piping components.
ASME B31J-2017 Standard provides a standard approach for the development of SIFs, k-factors, and sustained stress multipliers for collapse capacity of the metallic piping component or joint. It provides SIFs and k-factors compiled from test and analysis data for standard commercially available metallic components.
Table 3‑1. ASME B31 Code vs ASME B31J-2017
| ASME B31.1 Appendix D | ASME B31.3 Appendix D | ASME B31J-2017 | ||
| Title | Power Piping Mandatory Appendix D. Flexibility and Stress intensification Factors | Process Piping Appendix D. Flexibility and Stress intensification Factors | Stress Intensification Factors (i-Factor), Flexibility Factors (k-Factors), and Their Determination for Metallic Piping Components | |
| Bend | k-factor | (k) | (k) | Out-of-Plane (ko) In-Plane (ki) |
| SIF | (i) | Out-of-Plane (io) In-Plane (ii) |
Out-of-Plane (io) In-Plane (ii) Torsional (it) |
|
| Branch | k-factor | (k) =1 | (k) =1 | Run Out-of-Plane (kor) Run In-Plane (kir) =1 Run Torsional (ktr) Branch Out-of-Plane (kob) Branch In-Plane (kib) Branch Torsional (ktb) |
| SIF | (i) | Out-of-Plane (io) In-Plane (ii) |
Run Out-of-Plane (ior) Run In-Plane (iir) =1 Run Torsional (itr) Branch Out-of-Plane (iob) Branch In-Plane (iib) Branch Torsional (itb) |
4. Why ASME B31J-2017 should be used
The main purpose to use ASME B31J-2017 Standard is to improve the accuracy of the flexibility factors, Sustained Stress Indices, and Stress Intensification Factors applied to design. Application of these updated values can contribute to more realistic and predictable pipe stress analysis, which allows for a reduction of risk for failure.
Moreover, with the latest, fully tested data in ASME B31J-2017, pipe stress engineers have confidence they can provide an efficient design in accordance with the intent of the code – without unnecessary over or under conservatism.
ASME B31J Standard provides the “more applicable data” referenced in recent editions of the ASME B31 Codes as follows,
- According to ASME B31.1-2018 Appendix D General Notes (b),
“The designer may use the stress intensification and flexibility factors from ASME B31J instead of the stress intensification and flexibility factors herein. When using the stress intensification factors from ASME B31J, the maximum of the in-plane, out-plane, and torsional stress intensification factors shall be used in calculating stresses in accordance with para. 104.8. Alternatively, stress intensification factors may be developed using ASME B31J, Nonmandatory Appendix A.”
- According to ASME B31.1-2018 Chapter 119.7.3,
“In the absence of more directly applicable data, the flexibility factors and stress-intensification factors shown in Mandatory Appendix D may be used. Alternatively, ASME B31J may be used to determine stress-intensification factors.”
- According to ASME B31.3-2016 Chapter 319.3.6,
“In the absence of more directly applicable data, the flexibility factor, k, and stress intensification factor, I, shown in Appendix D shall be used for flexibility calculations described in para. 319.4. Stress intensification factors may be developed in accordance with ASME B31J.”
- According to ASME B31.3-2016 Chapter 319.4.4 and 320.2,
“when both ii(or Ii) and io(or Io) are determined by experimental or analytical means, e.g., ASME B31J.”
