Super Duplex 2507 Seamless Pipe | SA-790 | Tailan Metal

Super duplex 2507 seamless pipe is the 25 % chromium / 3.5 % molybdenum,
nitrogen-strengthened super duplex stainless steel supplied to
ASME SA-790. SA-790 covers two super duplex UNS numbers in the same
table, S32750 and S32760, and they are not
interchangeable: they have different chemistry, different PREN formulae and different
annealing windows.

SA-790 Scope 1.1 covers seamless and straight-seam welded ferritic/austenitic steel
pipe for general corrosive service, with particular emphasis on resistance to
stress-corrosion cracking, and warns that the steels are susceptible to embrittlement
if used for prolonged periods at elevated temperatures.

Dual Standard Designation

Chemical Composition (ASME SA-790, Table 2)

SA-790 Table 2 note A: values are maxima unless a range or minimum is indicated.
Note D, applying to S32750: % Cr + 3.3 × % Mo + 16 × % N
≥ 41. Note E, applying to S32760: % Cr + 3.3 × (% Mo + 0.5 × % W)
+ 16 × % N ≥ 41. These are the pitting-resistance-equivalent expressions and
they are not the same formula.

Mechanical Properties (ASME SA-790, Table 3)

SA-790 Table 3 note B: prior to A790/A790M-04, the tensile strength value for UNS
32760 was 109–130 ksi [750–895 MPa].

Size Range

Dimensions are taken from SA-790 Appendix Table X1.1, the ANSI B36.19
table for welded and seamless stainless steel pipe. Wall-thickness tolerances are not in
Section II; pipe dimensional tolerance is governed by SA-999 and the applicable
dimensional standard.

Standard Dimensions and Wall Thickness (ANSI B36.19 Schedule Table)

The nominal dimensions below are the published ANSI B36.19
schedule values, reproduced from ASME Section II SA-790 Appendix Table X1.1, which is
based on Table 1 of ANSI B36.19-1965. The decimal thicknesses are nominal or
average wall dimensions, which is how ASME defines them. Dimension and
thickness tolerances for the pipe itself are given by the governing product
specification and the applicable order requirements — tell us the NPS,
schedule and service condition and we will confirm the exact tolerance that
will be applied to your order.

Note A — Schedules 5S and 10S wall thicknesses do not permit threading in accordance with ANSI B1.20.1.
Note B — These do not conform to ANSI B36.10.

SA-790 Table X1.1 extends to NPS 30. ^B Note A: schedules 5S and 10S wall
thicknesses do not permit threading in accordance with ANSI B1.20.1. ^B Note B:
the marked wall thicknesses do not conform to ANSI B36.10-1979. Send us your NPS and
wall list and we will confirm availability against mill capability.

Manufacturing Route & Heat Treatment

SA-790 6.1.1 requires the pipe to be made by the seamless process or by an automatic
welding process with no addition of filler metal in the welding operation, 6.1.2 allows
hot-finished or cold-finished at the manufacturer’s option, and 6.1.3 requires the pipe
to be pickled free of scale (where bright annealing is used, descaling is not
necessary).

SA-790 Table 1 gives two different solution annealing windows for the two super
duplex grades: 1880 – 2060 °F (1025 – 1125 °C) for
S32750 and 1960 – 2085 °F (1070 – 1140 °C) for S32760,
both with rapid cooling in air or water. SA-790 6.3.1 allows the direct quench
immediately after hot forming as an alternative to a final furnace heat treatment,
provided the pipe is at or above the specified minimum solution treatment temperature.

Inspection & Certification

• Hydrostatic or electric test: SA-790 14.1, at the manufacturer’s
  option unless the purchase order states otherwise. SA-790 14.2 sets the stress used
  for the hydrostatic calculation to 50 % of the specified minimum yield strength
  of the pipe, with P = 2St/D per SA-999 22.2.1, and SA-999 22.2.2 caps the
  required test pressure at 2500 psi (17.0 MPa) for OD of 3.5 in. (88.9 mm) or less and
  2800 psi (19.0 MPa) above it.
• Electric test: SA-790 14.3, to Practices E213 or E309, performed
  after all mechanical processing, heat treatments and straightening (SA-790 14.4).
• Eddy-current and ultrasonic search: SA-790 14.8.2 caps the eddy
  current coil frequency at 100 kHz for walls up to 0.050 in., 50 kHz for walls up to
  0.150 in. and 10 kHz for walls over 0.150 in.; SA-790 14.8.3 requires a minimum
  nominal ultrasonic transducer frequency of 2.00 MHz and a maximum nominal transducer
  size of 1.5 in. SA-790 14.3.1.3 notes that ultrasonic testing may not detect short,
  deep defects, which is why the two methods are normally used to complement each other.
• Tension and hardness: one tension test per lot of not more than 100
  pipes, from two pipes for larger lots (SA-790 13.1); Brinell or Rockwell hardness on
  specimens from two pipes per lot (SA-790 13.4).
• Supplementary requirements: SA-790 S1 product analysis, S2
  transverse tension tests, S3 flattening test, S4 etching tests to Method E381, each
  applying only when specified on the purchase order.
• Certification: MTC to EN 10204 3.1 standard;
  EN 10204 3.2 issued when third-party inspection is specified on the order. PMI,
  intergranular corrosion testing and impact testing are available on request as
  supplementary requirements.

Packing & Delivery

Plastic end caps on all sizes; steel frames or wooden crates for large diameters; VCI
anti-rust wrapping. Beveled ends standard for welding; plain ends available. Each length
is marked with the standard, grade, size, heat number and heat treatment condition
(SA-790 16.1).

Applications

Seawater lift and discharge piping, reverse osmosis desalination plants, offshore
platform and subsea topsides piping, oil and gas sour service lines, chemical and
petrochemical process piping, pulp and paper bleach plant piping, flue-gas
desulphurisation scrubber inlet and outlet lines, and potable water chlorination and
distribution systems where chloride stress-corrosion cracking governs the selection.

Technical Notes

1. The two super duplex grades have two different PREN formulae, and only
one of them contains the tungsten term. SA-790 Table 2 note D, which applies to
S32750, requires % Cr + 3.3 × % Mo + 16 × % N ≥ 41. Note E, which
applies to S32760, requires % Cr + 3.3 × (% Mo + 0.5 × % W) + 16 × % N
≥ 41. The two numbers are not the same expression, because S32760 is deliberately
tungsten-bearing at 0.50–1.00 % with a narrower molybdenum window of
3.0–4.0 %, and the tungsten is credited at half weight in the molybdenum term.
S32750 gets no tungsten credit and instead relies on a wider molybdenum range of
3.0–5.0 % and the highest nitrogen in the group at 0.24–0.32 %. The
practical consequence is that a certificate written for one grade cannot be read
against the other, and that a project specification quoting a PREN figure must state
which of the two expressions it means.

2. S32760 and S32750 also differ in the tensile format on the certificate.
SA-790 Table 3 gives S32760 a single tensile minimum of 109 ksi (750 MPa) and carries
footnote B recording that the value was previously 109–130 ksi (750–895 MPa)
prior to A790/A790M-04. Meanwhile ASME SA-182 F 55 and SA-815 S32760 still carry the
109–130 ksi (750–895 MPa) range, because the change was made in the pipe
specification only. So the same UNS number can legitimately appear on a pipe
certificate as a 109 ksi minimum and on a forging or fitting certificate as a
109–130 ksi range. Neither is wrong; they are different documents. Read the
minimum that applies to the form you ordered. Note also that SA-790 assigns the common
name 2507 to S32750 only — S32760 appears in the same table with no common name
at all, so a line item reading “super duplex 2507” has not by itself
identified the grade.

3. Elongation and hardness move in opposite directions, and both matter.
S32750 carries the highest tensile minimum in the duplex group at 116 ksi (800 MPa) but
the lowest elongation minimum at 15 %, while S32760 gives 109 ksi (750 MPa) tensile with
25 % elongation. Elongation is the number that governs field operations: flaring,
expanding, bending and any cold-forming of a cut length, and it is the number a
fitter will hit first. Hardness runs the other way, with S32750 capped at 300 HBW / 32
HRC and S32760 at 310 HBW / 32 HRC, against 290 HBW / 30 HRC for 2205. The lower
elongation of S32750 is the direct price of its higher strength and higher nitrogen
content, and it is the reason a 2507 branch connection often needs a larger bend
radius or a heat-treatment allowance that a 2205 line would not.

Frequently Asked Questions

What is the difference between UNS S32750 and S32760?

S32750 is the standard super duplex 2507: molybdenum 3.0–5.0 %, nitrogen
0.24–0.32 %, no tungsten. S32760 is the tungsten-bearing variant: molybdenum
3.0–4.0 %, nitrogen 0.20–0.30 %, tungsten 0.50–1.00 %, copper
0.50–1.00 %. They use different PREN expressions and have different annealing
windows, so they are not drop-in substitutes for one another.

Which ASME specification covers super duplex 2507 pipe?

ASME SA-790, identical to ASTM A790/A790M. SA-789 is the tubing specification,
SA-182 covers the forged flanges and fittings (F 53 for S32750, F 55 for S32760), and
SA-815 covers the wrought fittings (WPS32750, WPS32760).

Can I substitute S32760 for S32750?

Not without a formal engineering check. The chemistry windows, the PREN expressions,
the annealing windows and the tensile requirements all differ. S32760 is normally
specified where reducing acid or sour service performance is critical, or where a 25 %
minimum elongation is needed for forming; S32750 is specified where the F 53 forging
grade and the widest molybdenum and nitrogen ranges are the requirement.

Is impact testing required?

Not by the base specifications for these grades. SA-182 9.7 applies the notch
toughness requirement to F 3V, F 3VCb and F 22V only, and SA-790 imposes no Charpy
requirement on S32750 or S32760. State any impact or corrosion testing requirement on
the order as a supplementary requirement and we will run it.

What certification is supplied?

EN 10204 3.1 mill test certificate as standard, with the heat treatment condition,
product analysis, tensile and hardness results. EN 10204 3.2 is issued when third-party
inspection is specified on the purchase order.

Are these pipes suitable for seawater?

That is the normal service for this material, and the 50 % PREN floor that SA-790
notes D and E impose is the specification’s own statement of the pitting margin
required. What the grade does not do is remove the need to control the service
temperature, because the scope warns that these steels are susceptible to embrittlement
if used for prolonged periods at elevated temperatures. Send us the chloride
concentration, temperature, oxygen level and crevice geometry and we will confirm the
grade against your service.

Inquire on WhatsApp