Zirconium Seamless Pipe | ASME SB-658 | Tailan Metal

Zirconium seamless pipe is supplied to
ASME SB-658 under UNS R60702. SB-658
covers three grades of seamless and welded zirconium pipe, and its Scope
1.1 states that the specification covers three grades of seamless and
welded zirconium pipe. Section 4.1 classifies the pipe in three grades:
R60702 unalloyed zirconium, R60704 zirconium-tin alloy, and R60705
zirconium-niobium alloy. The matching ASTM specification is B658/B658M.

This is a small-volume, high-consequence material. Zirconium is used
where the corrosion environment is severe enough that the nickel alloys
and the stainless steels are not adequate, and the specification is written
around the metallurgical risks that come with zirconium rather than around
the general ones.

Grades (ASME SB-658, Section 4.1)

Chemical Composition (ASME SB-658, Table 1)

Table 1 note A allows that, by agreement between the purchaser and the
manufacturer, analysis may be required and limits established for elements
and compounds not specified in the table. The two figures that carry the
most weight in this table are the hydrogen maximum of 0.005 % and the
oxygen maximum, and Section 7.2 makes the point that the manufacturer’s
ingot analysis is the chemical analysis for the piping
except for hydrogen and nitrogen, which shall be determined on the
finished product. Table 2 then gives the permissible variation in check
analysis between different laboratories for those and other elements.

Tensile Requirements (ASME SB-658, Table 3)

Table 3 note A states that when a sub-size specimen is used, the gauge
length shall be as specified in Test Methods E8/E8M for that specimen. The
tensile test itself is governed by 13.1, which requires the yield strength
to be determined by the offset (0.2 %) method and sets the strain rate at
0.003 to 0.007 in./in. [mm/mm]/min through the yield strength, after which
the cross-head speed may be increased to approximately 0.05 in./in. [mm/mm]/min
to failure.

Size Range (ASME SB-658, Table X1.1)

Table X1.1 is titled “Dimensions of Welded and Seamless Zirconium
Pipe”, and its note records that the table is from Table 1 of ANSI
B36.19 with the SI units added in this standard; note 2 of the specification
confirms that a system of standard pipe sizes approved by ANSI as ANSI
B36.19, reproduced as Table X1.1, applies pending the development of
similar standards for zirconium. The schedule set is therefore the same
5S / 10S / 40S / 80S system used for stainless steel pipe. Outside diameter
tolerances are in Table 4, and Table 4 note A states that the tolerances
apply to seamless pipe only, with tolerances on welded pipe to be agreed
between the manufacturer and the purchaser.

Manufacturing Route and Heat Treatment

SB-658 6.1 requires seamless pipe to be made from any seamless method
that yields a product meeting the specification, and 6.2 sets out the
requirements for pipe containing welded seams or other joints made by
welding: welding by welders, operators and procedures qualified under
Section IX of the Code, and filler metal, when used, of the same grade as
the base metal. Section 6.3 requires the pipe to be furnished in the
annealed or stress-relieved condition. Section 6.2.4 is the clause that
most often decides a project schedule: welds in grade R60705 shall be
stress-relief annealed within 14 days after welding to prevent delayed
hydride cracking, with the treatment consisting of holding the pipe at a
minimum temperature of 1100 °F [600 °C] for not less than 30 min per
inch [25 mm] of the maximum thickness in a nonreducing atmosphere, with a
minimum time at that temperature of 15 min, and all stress-relieved parts
cleaned subsequently and free of oxide scale contamination in accordance with
Practice B614.

Inspection, Testing and Certification

• Number of tests: SB-658 12.1 requires one longitudinal
  tension test per lot, 12.2 one chemistry test for hydrogen and nitrogen per
  lot of finished product, and 12.3 a hydrostatic proof test on each length of
  pipe.
• Hydrostatic test: SB-658 13.2 requires each pipe
  1/8 in. [3.2 mm] and larger in outside diameter, and with wall thickness of
  0.015 in. [0.4 mm] and over, to be tested to a hydrostatic pressure
  sufficient to produce a fibre stress of three-fourths of the minimum yield
  strength of the pipe, provided the test pressure does not exceed 5000 psi
  [35 MPa], calculated as P = 2St/D. The clause also requires the test to be
  performed prior to dimensional checks, upsetting, swaging, expanding or
  other forming operations.
• Radiography of butt welds: SB-658 13.4 requires that
  when specified in the purchase order, all butt welds shall be 100 %
  radiographed or x-rayed in accordance with ASME Code Section VIII,
  paragraph UW-51.
• Inspection: SB-658 14.1 requires the manufacturer to
  inspect the material prior to shipment at the manufacturer’s expense
  unless otherwise specified, and 14.2 requires the manufacturer to afford the
  purchaser’s inspector all reasonable facilities to verify conformance.
• Certification: SB-658 16.1 requires a producer or
  supplier to furnish a certificate that the material was manufactured,
  sampled, tested and inspected in accordance with the specification and has
  been found to meet the requirements, including a report of the test results.
• Product marking: SB-658 18.1 requires each length of
  pipe 3/8 in. [9.5 mm] nominal diameter and larger to be marked legibly with
  the manufacturer’s private identifying mark, the ASTM designation, the
  grade and the heat number, with the same information stamped on a metal tag
  for smaller sizes that are bundled.
• Section VIII supplementary requirement: S1 covers pipe
  produced for use in ASME BPV Code Section VIII construction, including
  filler metal qualified to Section IX, Section VIII heat treatment and
  nondestructive examination requirements, authorized inspection at the point
  of manufacture, the application of the Certification Mark, and the
  furnishing of an applicable ASME Partial Data Report form signed by an
  Authorized Inspector with a certified mill test report for each lot.

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, heat number
and heat treatment condition, and each length is marked so as to identify it
with the lot and the certified mill test report where S1 applies.

Applications

Hydrochloric acid production and handling, sulphuric acid service where
the concentration and temperature permit, pulp and paper bleaching plant
piping, nuclear fuel reprocessing and fuel-cycle installations, chemical
process lines carrying hot concentrated acids, and pharmaceutical and
specialty chemical process piping. The common requirement is an environment
severe enough to rule out the nickel alloys and the stainless steels.

Technical Notes

1. The 14-day rule is the specification telling you that
zirconium welds are not like other welds. Section 6.2.4 requires
welds in grade R60705 to be stress-relief annealed within 14 days after
welding specifically to prevent delayed hydride cracking, with the
treatment being a hold at a minimum of 1100 °F [600 °C] for not less
than 30 min per inch [25 mm] of the maximum thickness in a nonreducing
atmosphere and a minimum time of 15 min, followed by cleaning in accordance
with Practice B614. The reason is that zirconium absorbs hydrogen readily
when welded in the presence of moisture, and the hydrogen is not released
by ordinary cooling; it stays in the weld metal and the heat-affected zone
until the material is heated above the hydride transformation temperature.
A weld that is allowed to sit for weeks in service before the stress relief
is done is a weld that has been sitting in a hydrogen-charged condition for
weeks. Note also the two related requirements that make this workable: 6.2.1
requires the welding to be performed by welders, operators and procedures
qualified to Section IX, and 6.2.2 requires that any filler metal used be
of the same grade as the base metal.

2. Hydrogen and nitrogen are measured on the finished product, and
that is not a technicality. Section 7.2 states that the
manufacturer’s ingot analysis shall be considered as the chemical
analysis for the piping, except for hydrogen and nitrogen, which shall be
determined on the finished product. Ingot analysis and finished-product
analysis are not the same thing for these two elements, because the pipe is
formed and heat treated after melting, and the surface is cleaned and
handled between those steps. The specification therefore requires the
measurement that is actually predictive of behaviour. The limits are tight
in absolute terms: hydrogen at 0.005 % maximum and nitrogen at 0.025 %
maximum, against an oxygen maximum of 0.16 % for R60702. Oxygen is the
element that gives zirconium its strength, and the way it does that is
through the formation of oxide dispersion; a rising oxygen content makes
the material stronger and less ductile, and a rising hydrogen content makes
it more prone to hydride formation. The two limits pull in opposite
directions on ductility, and the finished-product measurement of hydrogen
and nitrogen is how the specification keeps that balance under control.

3. The dimensional basis is a borrowed standard, and the
specification says so openly. Note 2 to Section 9 records that a
system of standard pipe sizes approved by ANSI as ANSI B36.19, reproduced as
Table X1.1, applies pending the development of similar standards for
zirconium, and the appendix note records that Table X1.1 is from Table 1 of
ANSI B36.19 with the SI units added. Table 4 then adds a qualification that
matters for a mixed order: its note A states that the outside diameter
tolerances apply to seamless pipe only, and that tolerances on welded pipe
are to be agreed between the manufacturer and the purchaser. So the
dimension table is shared with stainless steel pipe, but the tolerance
regime is not, and the difference has to be established in the purchase
order for any order that mixes forms. Two further points from the same
section: 9.1.2 warns that thin-wall pipe, defined as having a wall
thickness of 3 % or less of the outside diameter, develops significant
ovality during final annealing or straightening, and the diameter
tolerances of Table 4 are not sufficient to provide for the additional
ovality expected in thin-wall pipe, with the difference in extreme outside
diameter readings in any one cross section not to exceed 1.5 % of the
specified outside diameter.

Frequently Asked Questions

Which ASME specification covers zirconium pipe?

ASME SB-658 (identical with ASTM B658/B658M), which covers three grades
of seamless and welded zirconium pipe: R60702 unalloyed, R60704 zirconium-tin
and R60705 zirconium-niobium. The seamless and welded zirconium tube form
is a separate specification, and welded zirconium fittings are covered
separately again.

What is the difference between R60702, R60704 and R60705?

R60702 is unalloyed zirconium with a minimum of 99.2 % zirconium plus
hafnium. R60704 is the zirconium-tin grade with 1.0–2.0 % tin, and
R60705 is the zirconium-niobium grade with 2.0–3.0 % niobium. The
tensile strength rises across the three, from 55 ksi (380 MPa) for R60702 to
80 ksi (550 MPa) for R60705.

Why does the specification put a 14-day limit on stress relief of welds?

SB-658 6.2.4 requires welds in grade R60705 to be stress-relief annealed
within 14 days after welding to prevent delayed hydride cracking, with a
hold at a minimum of 1100 °F [600 °C] for not less than 30 min per
inch of the maximum thickness in a nonreducing atmosphere and a minimum time
of 15 min, followed by cleaning to Practice B614. Zirconium absorbs
hydrogen during welding and does not release it on ordinary cooling, so the
stress relief cannot be deferred indefinitely.

What is the hydrostatic test pressure for zirconium pipe?

SB-658 13.2 requires a fibre stress of three-fourths of the minimum yield
strength of the pipe, calculated as P = 2St/D, provided the test pressure
does not exceed 5000 psi [35 MPa]. The test applies to pipe 1/8 in. and
larger in outside diameter with wall thickness of 0.015 in. and over, and
must be performed before any forming operation.

How is zirconium pipe marked and certified?

SB-658 18.1 requires each length of pipe 3/8 in. and larger to be marked
with the manufacturer’s private identifying mark, the ASTM
designation, the grade and the heat number, and 16.1 requires a
certificate that the material was manufactured, sampled, tested and
inspected in accordance with the specification, including a report of the
test results. Where the pipe is for Section VIII construction, S1 requires
an ASME Partial Data Report signed by an Authorized Inspector with a
certified mill test report for each lot.

Are hydrogen and nitrogen measured on the ingot or on the finished pipe?

On the finished product. SB-658 7.2 states that the manufacturer’s
ingot analysis shall be considered as the chemical analysis for the piping,
except for hydrogen and nitrogen, which shall be determined on the finished
product. The limits are 0.005 % for hydrogen and 0.025 % for nitrogen, with
Table 2 giving the permissible variation in check analysis between different
laboratories.

Inquire on WhatsApp