Hydrocarbon Processing - May 2021 - 51

Maintenance and Reliability
procedure specifications. If any
dehydrogenation heat treatment
repair activity, then that cracked
defects need to be removed on
is recommended on the parent
portion and nearby area should
the parent metal, then the parent
metal for at least 1 hr. The heating
be subjected to additional in-situ
metallography studies for
further assessment.
The vessel and reactor operating in a refinery
*	 Prior cleaning: Before
starting the grinding
may undergo various deteriorations due to their
process, the surface of the
operating conditions. Therefore, to protect the vessel
weld overlay metal should
be cleaned thoroughly to
and reactor from such deteriorations, the inner
remove scales, rust, carbon
surface of the wall should be cladded by stabilized
or any hydrocarbon deposits.
After removing 3 mm from
austenitic stainless-steel grades.
the weld overlay portion,
the fresh surface should
metal should be preheated to
rate is 100°C/hr/in. and the
be cleaned thoroughly to remove
315°C/hr/in. and, subsequently,
soaking temperature should be
any oxide scales. If any cracks are
the weld should be built up
300°C/hr/in., followed by air
discovered, they should be verified
by E8018 B3L or E-80S B3L
cooling at 100°C/hr/in. If any
by visual examination and dye
electrode or filler wire, depending
diffusible hydrogen content on the
penetrant testing.
on the type of welding process.
parent metal is found, it should
*	Grinding: The disbonding at an
*	 Heat treatment: The parent base
be removed prior to starting any
interface should be repaired as per
metal should be spot-heat treated,
welding process.
the applicable construction code.
and the heat treatment should
*	 Design to meet ASME
Depending on the type of flaw and
be completed on the base metal
standards: After removing the
locations, as well as the type of weld
prior to starting the weld overlay.
weld overlay portion inside the
overlay material and base metal,
Based on various metallography
reactor, the repair should be carried
the flaw should be ground out. It is
and other test results, the spotout to rebuild the wall thickness
recommended not to use thermal
heat treatment should be
as per the original specified
gouging during the flaw removal
recommended on the intended
drawings. The flawed portion
process. The grinding should be
repair area. The heat treatment
removed from the weld overlay
initially at the weld overlay portion,
procedure is shown in TABLE 1.
should be prepared for welding,
and grinding wheels should be
and adequate access should be
used as with the same stainless*	 Weld overlay restoration:
provided for the welding operation
steel grades of the weld overlay.
After completing the heat
to avoid lack of penetration, slag
Grinding should be optimized
treatment on the parent metal,
entrapment and improper fusion.
by controlling the speed of the
the weld should be overlaid
Prior to welding loosening or the
grinding wheel to remove the weld
on top of the parent metal
detaching of stiffener rings, the
overlay portion, and enough care
as per the welding procedure
installation of insulation support
should be taken to not overload
specification.1,2
rings and a reinforcing saddle
the speed of the grinding wheel
Repair that has affected the parent
should be carried out.
or the metal removal rate. The
base metal. If the defect has affected the
*	Welding: The welding should
removal of metal in the weld overlay
be produced via applicable
region should produce an even
construction codes as per welding
surface finish throughout the repair
process, and the grinding load
should be light enough to avoid
TABLE 1. Heat treatment procedure in
any unwanted defects. Preheating
repair work5
before grinding is recommended
Minimum criteria
to produce smooth surfaces and
Parameters
per ASME code
to promote easy removal of the
Heating rate
100°C/hr/in. thickness
weld overlay metal until the wheel
reaches the base metal. However,
Soaking time
1 hr/in. thickness
the parent metal should not be
Soaking temperature 675°C (min.)-
ground out unless other directions
730°C (max.)
were provided to do so after
Cooling rate
100°C/hr/in. thickness
obtaining all assessment reports
Heating methods
Electric resistance/
from metallurgical and NDTs.
induction heating
FIG. 3. Schematic of the vessel wall adjacent
*	 Hydrogen bake-out: After
to the internal load-bearing section.
Cooling methods
Air cooling
removing the weld overlay, a spot
Hydrocarbon Processing | MAY 2021 51
Hydrocarbon Processing - May 2021

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