Q: In two Materials Q&A columns back in Winter 2010 and Spring 2010, you discussed making flanges from forged bar, and in the Spring column you indicated that it would be interesting to submit an inquiry to ASME regarding the conflicting requirements in the Section II material specifications vs. Section VIII Appendix 2. Was that ever done?
A: Yes, it was,―and a little over 2 1/2 years later, a partial response was received.
The inquiry questions and replies were as follows:
1. Question: Is it acceptable to machine hubbed flanges from forged bar that meets the requirements for a material specified in SA-105, SA-181, SA-350, SA-182, or SA-522?
Reply: A revision record has been opened to address your inquiry regarding UG-14.
Note: UG-14 covers the material form “Rods and Bars.”
2. Question: If the answer to question number 1 is “Yes,” then is it acceptable to certify that the flanges machined from such forged bar are compliant with the pertinent material specification, even though the material specification prohibits machining flanges from forged bar?
Reply: No reply was required, because the reply to the previous question was not “Yes.”
3. Question: From the standpoint of Section VIII Division 1 Appendix 2 Paragraph 2-2 (d) (1), is radially-forged bar considered to be forged bar?
4. Question: Is there a specific definition of hot-rolled billet to distinguish it from hot-rolled bar with respect to Section VIII Division 1 Appendix 2 Paragraph 2-2 (d) (1)?
Reply: Yes. Definitions for billets and blooms exist in SA-788.
5. Question: If the answer to question number 5 is “No,” then should a definition be developed and added to Section VIII Division 1 Appendix 2 Paragraph 2-2 (d)?
Reply: No reply was required, because the reply to the previous question was “Yes.”
The ASME responses to the first two questions didn’t help to resolve this situation, at least in the short term. It’s assumed that the aforementioned revisions to the Section II specifications and/or revisions to Section VIII will eventually resolve the issue.
The response to the third question simply confirmed that radially-forged bar is considered forged bar, which helps alleviate concerns that it might be necessary to compress a bar shape in the longitudinal direction in order for it to be considered “forged.” We now know that is not necessary.
Regarding the response to question 4, following are the paragraphs from ASME SA-788 regarding billets and blooms:
3.3 Billets and Blooms—Interchangeable terms representing hot-worked semi-finished product intended as a starting stock for making forgings.
3.3.1 Discussion—No size limitations are assumed for either term. Cast shapes produced by a continuous casting process, without subsequent work, are considered to be ingots for the purposes of this specification, and if supplied as billets or blooms must carry the descriptor Cast Billet or Cast Bloom.
What this means is that hot-worked billets and blooms are distinguished from hot-rolled bar by:
- the fact that they are semi-finished, and
- their intended use (as a starting stock for making forgings).
Note that there are no physical criteria, such as size restrictions or reduction ratios from the original ingot cross-sectional area, etc. This seems problematic because anyone could consider a large hot-rolled bar to be semi-finished, and claim it was intended to be used as a starting stock for making forgings, qualifying it as a hot-worked billet or bloom. It could then be machined into a hubbed flange under the rules of Section VIII Appendix 2.
After further investigation, including discussions with code specialists, customers and authorized code inspectors, a better understanding of this situation has been established.
As stated in previous columns, Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code specifically allows the use of hubbed flanges machined from forged bar in accordance with the following statement from Mandatory Appendix 2, paragraph 2.2 (d) (1):
“Hubbed flanges may be machined from a hot-rolled or forged billet or forged bar. The axis of the finished flange shall be parallel to the long axis of the original billet or bar.”
Although this appendix allows the use of forged bar, it doesn’t state the specifications and grades that can be used, and it doesn’t mention the ASTM or ASME standards commonly used to cover forged flanges. In other words, it says you can make hubbed flanges out of forged bar, but it doesn’t provide any indication about how those hubbed flanges should be certified.
It would be ideal if there were ASTM or ASME specifications covering forged bar, but there aren’t. There are specifications covering some grades of bar that correspond with the ASTM and ASME standards and grades commonly used to cover forged items (Table 1).
Unfortunately, none of these covers forged bar specifically. SA-479 covers hot-finished (which would include, but not require, hot-forging), cold-finished and extruded material. SA-696 and SA-739 cover “hot-wrought” material, which would include, but not require, hot-forging. Since none of these specifications include a standard grade, class, form or other option to indicate that the bar is to be forged, the requirements for a forged bar version of each of these materials would need to be covered by an additional specification.
In addition, a number of steel grades are not covered under either SA-696 or SA-739. For example, there is no coverage for an impact-tested, low-temperature carbon steel (analogous to ASME SA-350 LF2 Class 1). SA-739 includes no coverage for a grade 91 material analogous to ASME SA-182 F91. Therefore, user specifications covering the compositions, manufacturing requirements, heat treatment requirements, mechanical testing requirements, certification requirements, etc., would need to be developed for any grades that are not specifically covered.
Another issue to consider is the acceptability of these materials under the various ASME codes. For example, according to Section II Part D, ASME SA-696 Grade C is acceptable per Section III, but not per Section I or Section VIII Division 1. ASME SA-739 B22 is acceptable per Section III and Section VIII Division 1, but not per Section I. In contrast, actual forged flanges compliant with SA-105 and SA-182 F22 Class 3 are acceptable under all of these codes.
So, in a nutshell, the situation can be summarized as follows:
- Section VIII Division 1 allows hubbed flanges designed in accordance with its own rules to be machined from forged bar.
- Such flanges machined from forged bar cannot be certified to be compliant with SA-105,
- SA-181, SA-182 nor SA-350. They must be certified to be compliant with some other specification.
- ASME specifications exist for wrought bar, but must be modified by user specifications to cover forged bar.
- Some material grades are simply not covered in these bar specifications, so user specifications would need to be developed to cover these “missing” grades.
- Not all ASME codes allow the use of SA-696 and SA-739, so the applicability of materials covered by these specifications, as well as by user specifications, might be prohibited under certain code sections.