Hydrocarbon Processing - May 2021 - 55

Maintenance and Reliability
TABLE 3. Welding procedure speciﬁcations for the GTAW process (CONT.)
Gas (QW-408)
Gas

% composition (mixture)

Flowrate

Shielding

Not applicable

Not applicable

Not applicable

Trailing

Not applicable

Not applicable

Not applicable

Backing

Not applicable

Not applicable

Not applicable

Electrical characteristics (QW-409)
Filler metal
Weld passes

Process

Classiﬁcation

Diameter, mm

Current type
and polarity

Ampere
in range

Travel speed in
range, mm/min

Volts in
range, v

Barrier overlay

SMAW

E-309 Nb

3.15

DCEP

80-100

107-140

22-26

1.6

Barrier overlay

SMAW

E-309 Nb

4

DCEP

100-130

127-165

22-26

1.6

Energy input

Weld overlay

SMAW

E-347

3.15

DCEP

80-100

Not available

22-26

Not applicable

Weld overlay

SMAW

E-347

4

DCEP

100-130

Not available

22-26

Not applicable

Tungsten electrode size and type

Not applicable

Welding technique (QW-410)
String or weave bead

String or weave bead

Oriﬁce, nozzle or gas cup size

Not applicable

Initial and interpass cleaning (brushing, grinding, etc.)

Stainless-steel wire brush or stainless-steel wheel grinding

Method of back-gouging

Not applicable

Oscillation

Not applicable

Contact tube to work distance

Not applicable

Multiple passes or single pass (per side)

Multiple passes per side

Multiple or single electrodes

E-309 Nb followed by E-347

Electrode spacing

Not applicable

Peening

No peening

and tempered condition). No
defect should be present on the new
parent plate metal. The minimum
diameter of the new plate should be
at least 380 mm, with a maximum
of 2,184 mm, depending on the
location of the replacement and
considering cutouts for attached
piping or any other system (e.g.,
nozzles). This cutout in the reactor
wall should be assessed and
prepared as per original drawings.
The edges of the new plate should
be prepared by machining or
grinding. The edges should be
subjected to NDT, and all defects
must be removed and repaired.
Additionally, the edge alignment of
the new plate should be within the
applicable design code.
* Welding: The welding should
be a full-penetration butt weld of
the double-v groove joints. The
filler metal and electrode chosen
should be based on the type of
welding process. Before the joint
is welded, it should be preheated
to a maximum of 315°C/hr/in.

thickness. The weld joint should
use an E8018 B3L electrode or
E-80S B3L filler wire for singlemetal arc welding (SMAW) or
gas-tungsten arc welding (GTAW),
respectively. Prior to welding,
any grease, oil and/or scales
must be cleaned off to avoid weld
contamination. Welding procedure
specifications for SMAW and
GTAW are detailed in TABLE 2 and
TABLE 3, respectively.
* Quality before post-weld heat
treatment (PWHT): The final
weld joint should be produced
with minimum distortion, as
well, to avoid a lack of fusion and
penetration or any other defects.
The final weld should have a
smooth surface finish. The welding
procedure qualification (WPQ) of
the parent metal welding should
be subjected to impact tests. An
impact test is mandatory for WPQ
to produce reliable weld metal.
The new plate should be 100%
radiographed. After completing
the weld, the full penetration joint

should be 100% radiographed to
ensure sound weld quality.
* PWHT of the replaced plate: After
ensuring quality, the thick-welded
joint should undergo PWHT, which
should be carried out only in weld
joints. The PWHT chart should be
equivalent to TABLE 1.5
* Non-destructive evaluation after
PWHT: After completing the
PWHT, the weld joints should be
subjected to 100% radiography.
This will ensure that no new
defects were generated after the
PWHT process. Before resuming
its service, the entire reactor, or at
least the repaired portion of the
reactor, should be subjected to a
leak test or hydrotest to confirm
the quality of the repair.
REFERENCES
ASME BPV Code Sec 9
2
ASME BPV Code Sec 8
3
ASME BPV Code Sec 5
4
ASME PCC-2
5
ASME BPV Code Sec 2 A
6
ASME BPV Code Sec 2 C
7
API RP 579, Fitness for Service
1

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