MATERIALS Q&A BYDONBUSH
Q: In the last Materials Q&A column,
you discussed using forged bar to
make hubbed-flange components such
as bonnets. I noticed that ASTM A182
specifically states that forged bar
cannot be used for flanges. Was your
original statement in error?
A: Thank you for pointing this out.
ASTM A182 paragraph 4. 5 does
include the statement:
“Except for flanges of any type, forged or
rolled bar may be used without additional
hot working for small cylindrically shaped
parts within the limits defined by Specifi-
cation A 234/A 234M for low alloy steels
and martensitic stainless steels and Speci-
fication A 403/A 403M for austenitic and
ferritic-austenitic stainless steels.”
This would seem to prohibit the use of
forged bar to make flanges per ASTM
A182. This same statement exists in the
other “forging” specifications in various
forms. ASTM A105 refers to ASTM
A961 Section 6, which includes the fol-
lowing statement:
“Flanges, elbows, return bends, tees,
and header tees shall not be machined
directly from bar.”
Note that it does not specifically indi-
cate the type of bar (i.e., hot-rolled or
forged) that may not be used, so this
would seem to imply that all bar, includ-
ing forged bar, would be unacceptable to
produce any type of flange.
Other specifications such as ASTM
A181, A350, A522 and A727, include
statements that specifically prohibit the
use of forged bar for flanges of any type.
The exact wording in these specifications
varies slightly, but the requirements are
essentially the same. The wording from
ASTM A350 paragraph 5. 3. 3 is:
“Other parts, excluding flanges of all
types, may be machined from hot-rolled or
forged bar up to and including NPS 4.”
This would appear to be an open-and-
shut case against the use of forged bar to
make hubbed-flange components. Howev-
er, consider the following definitions,
which were developed by combining definitions and discussion points from both
ASTM A788 and A961:
Forging: The product of a substantially
compressive hot or cold plastic working
operation that consolidates the material
and produces the required shape. The
plastic working must be performed by a
hammer, press, forging machine, or ring
rolling machine, and must deform the
material to produce a wrought structure
throughout the material cross section.
Forged Bar: A forging that has no
bore, with a relatively constant cross section throughout its length and with an
axial length greater than its maximum
cross-sectional dimension, and a wrought
microstructure throughout the material
cross section. Note that radially-forged bar
meets this definition.
Now consider the fact that the ASME
Boiler and Pressure Vessel Code specifi-
cally allows the use of hubbed flanges
machined from forged bar per Section
VIII, Division 1, 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.”
This situation creates quite a paradox.
Let’s assume that a valve company or a
subcontracted machine shop machines a
hubbed-flange bonnet from a piece of
forged bar (not hot-rolled bar) that is cer-
tified to ASTM A350 Grade LF2 Class 1.
The $64,000 question then becomes:
How should the component be marked
and certified?
On the one hand, ASTM A350 explic-
itly prohibits the use of forged bar to
make flanges of all types. Per paragraph
5. 3. 2, it states:
“The finished product shall be a forg-
ing as defined in the Terminology section
of Specification A788.”
How can the bonnet be marked and
certified as an “ASTM A350 LF2 Class
1” component when ASTM A350 does
not allow the manufacture of any flanged
component from forged bar?
DON BUSH is a principal materials engineer at
Emerson Process Management-Fisher Valve Division ( www.emersonprocess.com). Reach him at
Don.Bush@Emerson.com.
