- Published on Tuesday, 19 January 2010 00:00
- Written by Don Bush
Q: I have a material certification for bar material that indicates compliance with ASTM A105. Is this forged bar? Can I use it to make hubbed-flange items?
A: ASTM A105 “Carbon Steel Forgings for Piping Applications” includes the following requirement:
4.2 Except as permitted by Section 6 in Specification A961, the finished product shall be a forging as defined in the Terminology Section of Specification A788.
Paragraph 61.1 of ASTM A961 “Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping Applications” states:
6.1.1 Bar - Flanges, elbows, return bends, tees, and header tees shall not be machined directly from bar. Other hollow cylindrical shaped parts up to, and including, NPS 4 can be machined from bar provided that the axial length of the part is approximately parallel to the metal flow lines of the starting stock.
Therefore, a market for bar (usually by hot-rolling) meeting A105 chemistry and mechanical property requirements exists and can be used for hollow cylindrical machined components falling within this definition. Note that ASTM A350 “Carbon and Low-Alloy Steel Forgings, Requiring Notch Toughness Testing for Piping Components” includes similar wording, so there is also demand for bar stock certified to ASTM A350 LF2
Class 1. Many bar manufacturers currently produce hot-rolled bar per ASTM A105 and ASTM A350 LF2 Class requirements. In fact, it is quite common for certified material test reports (CMTRs) to indicate compliance with both A105 and A350 LF2 Class 1, which is accomplished by ensuring chemistry and tensile test compliance with both materials and adding Charpy impact testing to meet the A350 LF2 Class 1 requirements.
Bar certified per ASTM A105 can be used for some components, but it cannot be used for hubbed flange components such as weld-neck flanges and bolted valve bonnets. Unfortunately, the CMTRs for these materials do not always clearly indicate whether the bar is forged or simply hot-rolled. For example, here are a few sample descriptions from CMTR that indicate compliance with A105 and/or A350 LF2:
- Rd 6.000”Diam x 20’RL (6-inch diameter by 20 feet, random lengths)
- 4 Bars 6” x 21’11”/22’07”
- 7.250 in Rd, Hot Roll – Quench – Temper – Straighten (this CMTR actually indicates that the bar is hot-rolled)
- 4.5” round – Continuous Cast, Roll Reduction 9:1 (this material was actually radially forged from continuously-cast round ingot, but the CMTR did not include any indication the bar was forged)
Where Confusion Lies
As this shows, it may be difficult for someone reviewing a CMTR to determine if the bar is forged or not.
In addition, if you look at this situation from the viewpoint of a manufacturing plant or a contract machine shop, you can see further confusion. Consider the case of a hubbed-flange valve bonnet being produced by a contracted machine shop. The specification for the bonnet is “Carbon steel per ASTM A105.” If no further instructions are provided to the machine shop, personnel will be tempted to go to bar suppliers and ask what ASTM A105 material is, and whether those suppliers can provide it. Since A105-certified bar material is available, personnel may purchase the hot-rolled bar and machine the bonnets. Since the CMTRs state compliance with ASTM A105, these bonnets could make it through all inspection steps and be used in production assemblies. The inconsistency would only be identified if:
- Someone along the way decided to read the appropriate section in the A105 specification, and
- noticed that hubbed-flange items must be made from forgings, and
- realized that bonnets are hubbed-flange items, and
- could identify based on the CMTR that forged bar had not been used.
This situation has arisen to a large extent because the titles of these specifications imply that only forgings may be used for components. In addition to ASTM A105 and A350, the following specifications also allow the use of bar for some components, even though the titles of the specifications would lead one to believe the product must be a forging:
- ASTM A181“Carbon Steel Forgings, for General-Purpose Piping”
- ASTM A1021 “Martensitic Stainless Steel Forgings and Forging Stock for High-Temperature Service”
ASTM A182 is entitled properly: “Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service.” The bottom line is that, for any of these specifications, the only way to ensure hubbed flange components are produced from forgings or forged bar is to attach a supplementary specification to those components stating specifically they must be produced from forgings or forged bar. Otherwise, there is a good chance that manufacturing sites or third-party machine shops will, in good faith, think they are meeting requirements by machining these components from hot-rolled bar material that they believe is acceptable.