Duplex 2205 Welded Pipe | SA-790 | Tailan Metal

Duplex 2205 welded pipe is the same 22 % chromium / 3 % molybdenum
nitrogen-strengthened ferritic-austenitic stainless steel as the seamless grade,
supplied to ASME SA-790 under UNS S32205 in
straight-seam welded form. 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.

Two clauses define this product and they are not the same clauses that define the
seamless grade. 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, and SA-790 6.3.2 provides a specific route for pipe that is
fabricated from plate and is not given a final heat treatment after welding.

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.
Copper and other elements are not required for these two grades.

Mechanical Properties (ASME SA-790, Table 3)

Size Range

Dimensions are taken from SA-790 Appendix Table X1.1, the ANSI B36.19
table for welded and seamless stainless steel pipe. SA-790 6.1.1 requires the pipe to be
made by an automatic welding process, so the seam is longitudinal and the OD follows
the B36.19 series. 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 an automatic welding process with no addition of filler metal
in the welding operation, so the weld metal chemistry is the base metal chemistry.
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, with descaling not necessary where bright
annealing is used.

SA-790 6.3 requires the pipe to be furnished in the heat-treated condition shown in
Table 1 unless the order states otherwise, with S32205 solution annealed at
1870 – 2010 °F (1020 – 1100 °C) and rapidly cooled in
air or water. SA-790 6.3.2 provides the alternative for plate-fabricated pipe: where the
purchaser wants no heat treatment subsequent to welding, the purchase order must state
that condition, no final heat treatment of pipe fabricated from plate that has already
been heat treated as required by Table 1 is needed provided a sample of that heat of
finished pipe, or material representing that heat as a prolongation of the weld passes
Test Methods A923 Method B or C — including base metal, weld metal and heat
affected zone per heat — and each pipe supplied under this requirement is
stenciled with the suffix “HT-O”. SA-790 6.3.2.2 adds that the HT-O
provision does not apply to materials not listed in Table 3 of Test Methods A923.

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 hydrostatic
  stress at 50 % of the specified minimum yield strength of the pipe,
  with P = 2St/D per SA-999 22.2.1. 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, and SA-999 22.2.4 requires the pressure to be held for at least 5 s, and for welded
  pipe for a time sufficient to permit the entire length of the welded seam to be
  inspected.
• Electric test: SA-790 14.3, to Practices E213 or E309, performed
  after all mechanical processing, heat treatments and straightening (SA-790 14.4).
• Flattening or guided bend: SA-790 13.3 requires the flattening test
  for pipe heat treated in a batch-type furnace on 5 % of the pipe from each
  heat-treated lot, and SA-790 13.3.1 allows a transverse guided face bend test in place
  of the flattening test for welded pipe of NPS 10 and larger, with specimens from 5 % of
  the lot taken from pipes or test plates of the same material as the pipe, the test
  plates being attached to the end of the cylinder and welded as a prolongation of the
  pipe longitudinal seam.
• Weld repair envelope: SA-790 15.1 permits weld repairs with
  compatible filler metal on welded pipe of NPS 6 and larger with a specified wall of
  0.188 in. (4.8 mm) or more, following the plate defect repair procedures of SA-999;
  15.2 limits the repair length to 20 % of the seam length; 15.3 requires gas
  tungsten-arc welding with bare filter rod qualified to AWS A5.9 as the grade being
  repaired per SA-790 Table 4 — for S32205 that is ER2209, UNS S39209;
  15.3.1 permits a more highly alloyed filler with purchaser approval; 15.4 requires
  repaired pipe to be identified with the symbol “WR” and stated on the
  certificate of tests; and 15.5 requires the repair to be completed before any heat
  treatment.
• Operator qualification: SNT-TC-1A or equivalent (SA-790 14.7).
• 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, A923 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 and cooling water systems, desalination plant intake and product piping,
oil and gas production facilities, chemical and petrochemical process lines, pulp and
paper bleaching plant piping, flue-gas desulphurisation scrubbers, and water treatment
piping, particularly where the size or the wall-to-diameter ratio makes seamless
production uneconomic.

Technical Notes

1. The longitudinal seam carries no filler metal, and that is deliberate
rather than an economy. SA-790 6.1.1 requires an automatic welding process with
no addition of filler metal in the welding operation. Because there is no filler, the
weld metal chemistry is the base metal chemistry, so the corrosion behaviour across the
seam matches the parent material and the chromium and molybdenum contents of the
weld do not fall below the ranges in Table 2. In a conventional filler-added weld on
a duplex grade, the filler is deliberately over-alloyed in nickel to compensate for
dilution by the base metal, and the weld region becomes the most likely place for a
chromium-depleted layer to appear. Avoiding filler removes that variable. The same
clause also means the inspection regime is different from a filler-added line: the
SA-790 13.3.1 guided face bend for NPS 10 and larger exists precisely to interrogate
the seam, and the SA-790 15.3 requirement that any repair be made by gas tungsten-arc
welding with matching AWS A5.9 filler keeps the repair chemistry consistent with the
original autogenous seam.

2. HT-O is the clause that makes welded duplex pipe economic, and it is
conditional. SA-790 6.3.2 lets the purchaser specify pipe that has not been
heat treated after welding, provided the pipe is fabricated from plate that has already
been heat treated to Table 1, and provided a sample of that heat — the finished
pipe or material representing that heat as a prolongation of the weld — passes
Test Methods A923 Method B or C, with base metal, weld metal and heat affected zone all
covered, per heat. The benefit is that a full solution anneal and quench of the
finished pipe, with all the furnace time and distortion control that goes with it, can
be avoided. The condition is the point: A923 is the intermetallic phase detection test,
and the reason it is required is that a duplex weld heat affected zone is the location
where a run of slower cooling can precipitate sigma and chi phases that are not
present in the unwelded plate. The pipe is then stenciled “HT-O” so that the
status travels with the material, and SA-790 6.3.2.2 closes the provision off for
materials not listed in Table 3 of A923. If your project is considering HT-O, confirm
with us that the grade and the heat are eligible before you write it into the
specification.

3. Weld repairs on duplex pipe are tightly bounded, and the bounds are in
the specification. SA-790 15.1 restricts repairs to welded pipe of NPS 6 and
larger with a specified wall thickness of 0.188 in. (4.8 mm) or more, and requires them
to follow the SA-999 plate defect repair procedures. SA-790 15.2 caps the repaired
length at 20 % of the seam length, so a seam that has been repaired more extensively
does not meet the specification and the length is not acceptable. SA-790 15.3 permits
only gas tungsten-arc welding for the repair, with bare filter rod qualified to the
most current AWS A5.9 as the grade of pipe being repaired, which for S32205 is ER2209
under UNS S39209 per SA-790 Table 4; 15.3.1 allows a more highly alloyed filler if
the purchaser approves it; 15.4 requires the repaired pipe to carry the “WR”
symbol and for the filler metal to be identified on the certificate of tests; and 15.5
requires the repair to be completed before any heat treatment. Read together, these
clauses mean a duplex pipe with a long or frequently repaired seam should not be
accepted on the basis of a mill certificate alone — ask for the repair
documentation with the certificate.

Frequently Asked Questions

Which ASME specification covers duplex 2205 welded pipe?

ASME SA-790, identical to ASTM A790/A790M, which covers seamless and straight-seam
welded ferritic/austenitic steel pipe in one document. SA-789 is the tubing
specification and SA-182 covers forged flanges and fittings.

Is the welded form chemically different from the seamless form?

No, and that is the point of SA-790 6.1.1. The pipe is made by an automatic welding
process with no addition of filler metal, so the weld metal chemistry is the base
metal chemistry and both forms carry the same Table 2 chemistry and Table 3
mechanical requirements.

What is the HT-O marking and when can it be used?

SA-790 6.3.2.1 requires each pipe supplied without a post-weld heat treatment to be
stenciled with the suffix “HT-O”. It is available where the pipe is
fabricated from plate already heat treated to Table 1 and a sample of that heat passes
Test Methods A923 Method B or C covering base metal, weld metal and heat affected zone.
The order must state the condition, and SA-790 6.3.2.2 excludes materials not listed in
Table 3 of A923.

Can weld seams be repaired, and what filler is used?

SA-790 15.1 permits repair of welded pipe of NPS 6 and larger with a specified wall
of 0.188 in. (4.8 mm) or more. SA-790 15.2 limits the repair to 20 % of the seam
length, and SA-790 15.3 requires gas tungsten-arc welding with AWS A5.9 filler matching
the grade — ER2209, UNS S39209, for S32205. Repaired pipe is marked “WR”
and the filler is identified on the certificate of tests.

Which nondestructive test is applied?

SA-790 14.1 requires each pipe to be subjected to either the nondestructive electric
test or the hydrostatic test, at the manufacturer’s option unless the purchase
order states otherwise, so state your requirement on the order. Electric testing is
to Practices E213 or E309 and is performed after all mechanical processing, heat
treatments and straightening.

What certification is supplied?

EN 10204 3.1 mill test certificate as standard. EN 10204 3.2 is issued when
third-party inspection is specified on the purchase order, and A923, intergranular
corrosion, PMI and impact testing are available on request.

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