ASTM (American Society for Testing Materials)
These are basically materials specifications. ASTMA A-403
(Factory Made Wrought Austenitic Steel Welding Fittings) lists the
permissible raw materials from which fittings can be made. In
addition, it controls the method of manufacture, quality assurance
The corresponding ASME Spec is SA-403. This is found in
Section II Part A of the ASME Boiler and Pressure Vessel Code.
This is similar, but not identical to ASTM A-403.
ASME (American Society of Mechanical Engineers) Boilers and
Pressure Vellel Code and MSS (Manufacturers Standardization Society)
Both ASME B 16.9 entitled "Wrought Steel Butt Welding
Fittings" and MSS SP-43 entitled "Wrought Stainless Steel
Butt Welding Fittings" cover 1/2" through 24" and
govern dimension and tolerance. The difference is that ASME B
16.9 covers all wall thicknesses and requires fittings to be fully
rated to the pressure temperature ratings of the matching pipe.
MSS SP-43 covers only light weight stainless steel fittings, and
allows lower pressure temperature ratings than B 16.9. See
below for details:
Other supplementary ASME and MSS standards:
ASME B 16.25 - Butt welding end preparations
ASME B 16.28 - Butt welding short radius elbows and returns 1"
MSS SP 25 - Marking of each fitting
ASME Section II - Materials. Part A - Ferrous; Part B -
Non-Ferrous; Part C - Welding Materials; Part D - Properties
ASME Section III - Nuclear Power Plant Components. For the
manufacture of fittings where filler metal is added, a Certificate
of Authorization (NPT Stamp) is required.
ASME Section V - Non-destructive examination
ASME Section VIII - Pressure vessels
ASME Section IX - Welding Qualifications
MSS SP-43 and ASME B16.9 for Schedules 5S and 10S Fittings
In response to the need of the process industries, SP-43
Specification was issued in 1950 by the Manufacturers
Standardization Society. At that time, stainless steel piping
was used for its resistance to corrosion and to eliminate product
contamination. Pressure was seldom a factor.
Pressure ratings for 5S and 10S fittings are shown in MSS
SP-43. They reflect the emphasis on corrosion resistance
rather than pressure. These pressure ratings are less than the
allowable pressure ratings that are applicable to the matching pipe.
Today there are many applications for schedules 5S and 10S piping at
higher pressures than those permitted in SP-43. To cover this,
SP-43 was revised to include a statement, "For fittings of same
pressure rating of matchine pipe, refer to ASME-B 16.9."
SP-43 and B 16.9 are similar dimensionally in that the fixed
position for the welding ends with reference to the centerline of
the fitting and the overall dimensions are identical.
ASME B 16.9 has the added provision that the pressure of the fitting
shall at least equal the computed bursting pressure of seamless pipe
of the same wall thickness and material.
In order to differentiate fittings made to these specifications, the
prefix "CR" is shown before the alloy designated for SP-43
and the symbol "WP" is shown to indicate B 16.9 fittings.
A user who wants to obtain 5S and 10S to B 16.9 fittings must
reference this Spec when ordering fittings to ASTM A-403. If B
16.9 is not specified, the manufacturer may supply either SP-43 or B
16.9 at his option.