National Conference on Recent Trends in Engineering & Technology
Defect Analysis in Dish End and Nozzle Joint of
Reactor Vessel
Prof. Purvi Chauhan Dr. Amit Trivedi
Department of Production Engineering, Department of Production Engineering,
B.V.M. Engineering College B.V.M. Engineering College
Vallabh Vidhyanagar-388120, Gujarat, India Vallabh Vidhyanagar-388120, Gujarat, India
pdchauhan@bvmengineering.ac.in pramukh1@gmail.com
Prof. K. D. Bhatt
Department of Production Engineering,
B.V.M. Engineering College
Vallabh Vidhyanagar-388120, Gujarat, India
kdbbvm@gmail.com
Mr. Hemant V. Suthar Mr. Yogesh R. Rana
Planning Officer, Senior Engineer
GMM Pfaudler Ltd. Elecon Engg. Co. Ltd.
hemant_suthar2004@yahoo.com yogesh_rana@yahoo.com
Abstract— ground to avoid tungsten inclusion [4]. To find out the defects
from the weld the non destructive testing methods namely
The welding joints of chemical reactor vessel assume the Liquid Penetration Test (LPT) and Ultrasonic Test (UT) are
significance as regards to protection of corrosion resistant glass deployed [5]. A case is presented to demonstrate the co-
lining and leakage of high pressure chemical species in and around
the weld joint. The present study aims at understanding the
relationship of weld parameters with the weld defects.
influence of welding parameters of one such critical weld joint
between dish end and nozzle of the reactor vessel. The influence of
welding current and welding speed on welding defects is critically
II. BRIEF OVERVIEW OF REACTOR VESSEL
studied considering four independent cases. The two common
defects observed in non destructive testing are porosity and slag
inclusion. The study reveals the safe window of operating
parameters for welding current and welding speed for the suggested
welding procedure.
Key Words: Reactor Vessel, welding Defects, GTAW welding
parameters, SMAW welding parameters
I. INTRODUCTION
A reactor vessel is a closed container designed to hold gases or
Side Bracket
liquids at a desired pressure and temperature for mixing or
producing a desired chemical reaction. The main components
of these reactor vessels are pan/mono-block, dish end and
nozzle [1]. The assembly of nozzle to dish end is done by
welding operation which is very critical and it could lead to
welding defects if process is not controlled as per welding
procedure [2]. The joint geometry of the nozzle and dish end is
single V- type butt joint. The major defects observed are Anchor Agitator
porosity and slag inclusion. The significant welding parameters
those are responsible for generating defects in welding are Bottom Outlet
welding current, arc voltage, welding speed, gas flow rate and
wind direction [3]. As current, voltage and speed govern the Figure - 1 Reactor vessel [6]
heat input predominantly they are considered for present The typical cross section of reactor vessel is shown in Figure-1.
analysis. The welding is carried out in an enclosure to restrain The basic components of the reactor vessel are pan/
the influence of the wind. The tungsten electrode is properly monoblock, top-dish, agitator, drive assembly and flush bottom
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
valve. The pan is used for holding the charge to be reacted, top IV. MAJOR DEFECTS IN THE WELDING
dish has the nozzle for loading the charge, manhole cover for The major defects observed in the present case are porosity and
visual inspection and maintenance, agitator shaft hole and slag inclusion [6-8].
support is used for agitator drive assembly. The agitator is used (1) Porosity
for the homogeneous mixing of the reactive items in the pan. It is a cavity type discontinuity formed by the gas entrapment
The drive assembly rotates the agitator and the flush bottom during solidification. Porosity is formed in weld metal when
valve is for unloading the chemicals from reactor. The drive dissolved gases present in the molten metal are entrapped due
assembly contains gear box, electrical motor, muff coupling, to their limited solubility limits at the room temperature [6-8].
mechanical seal as shown in Figure-1. The gases which may be present in the weld pool during
welding include H2, O2, N2, CO, CO2, H2O, H2S, Ar, or He and
III. JOINT GEOMETRY OF DISH END WITH NOZZLE H2, O2, N2 are considered soluble in molten weld pool to any
significant extent. The hydrogen gas is considered to be the
major cause of porosity in the welding of the materials such as
low carbon steel and aluminum. The main reasons for porosity
are high current and low travel speed, wind direction and
improper shielding, unbaked electrode and improper initiation
of re-striking electrode.
(2) Slag inclusion
Figure – 2 V- Joint geometry [6] Slag inclusion is formed due to entrapment of oxides or non
metallic solid material in the weld deposited between the weld
The typical joint geometry of the sample is shown in the metal and base metal. Due to their low specific gravity, the
Figure- 2[6]. The thickness for the plate is 16 mm and the slag normally floats over the molten metal unless it is
included angle of the weld joint is 55°. The root face is 1.5 to 2 restrained [6-8]. Because of the stirring action of the arc the
mm and the root gap suggested is 1.5 to 3 mm. In the reactor slag may be forced down below the molten metal and the high
vessel the nozzle is joined to the dish end by single ‘V’ joint as viscosity of the weld metal, rapid solidification at a low
shown in Figure - 3. temperature may prevent the release slag inclusion which
usually appears as a linear discontinuity or interrupted
bonding. The main reasons for the slag inclusion are faster
cooling rates, improper cleaning and improper bead geometry
[6-8].
V. EXPERIMENTAL DETAILS
The joint is prepared as per the weld joint detail given in
Figure- 2. The influence of current, speed and voltage are
presently studied on formation of defects [6].
1) Influence of the current
The welding current is varied for root pass weld by GTAW in
the range of 130-150 amps with 10 amp increments per step.
The first pass of weld by SMAW is varied from 160-180 amps
with 10 amp increments. All the subsequent pass of welding is
carried out in the range of 200-240 amps with increment of 10
amps each.
Figure - 3 V joint of dish end with nozzle [6] As per standard welding procedure [2-6] & design of
experiments carried out, the parametric details of experiment
The nozzle is joined to a swaged portion of the dish end. Here are shown in Table 1 and constant parameters are shown in
‘V’ joint is used because it is difficult to weld the nozzle to the Table 2.
dish end from both the side as making a double ‘V’ joint is a
difficult proposition. The ‘V’ joint of the surface is made by
gas cutting torch and subsequently ground [6]. To ease welding
the welding positioners are employed.
The root pass is carried out by gas tungsten arc welding
(GTAW) for sound initial pass and shielded metal arc welding
(SMAW) is carried out for subsequent passes for faster and
higher metal deposition.
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
Table 1: Variation of Welding Current for four cases
Case 2: The liquid penetration test for the given case showed
Current in ampere Defect no defect ensuring the absence of surface defect. In ultrasonic
location in test the defect was seen at 15.0 mm from the bottom of the
mm surface. The defect was located at a distance of 150 mm and
Process GTAW SMAW 230 mm respectively from the right side of the test piece. The
Case ROOT 1st Filling defect at the 150 mm is introduced due to striking and re-
pass pass passes striking of the electrode as the re-striking of electrode was
Case 1 130 160 200 5.8 mm from noticed on examination. As the arc is blown off, air entrapment
bottom (UT) in the molten metal has caused the defect. The defect at the
Case 2 140 170 220 15.0 from distance of the 230 mm is attributed to improper slag removal
bottom & 5 mm of earlier weld passes. In both the flaws observed in the
from top (UT) ultrasonic test the echo signals are crossing the limiting curve
Case 3 140 170 230 5.8 mm & 4.8 and are defect of severity.
mm from top
(UT)
Case 4 150 180 240 12.0 mm & 14.8 Case 3: In liquid penetration test for the given case no defect is
from bottom seen ensuring the absence of surface defect. In ultrasonic test,
(UT) the intermittent peak is observed at 5.8 mm from the top
surface and another flaw is located at 4.8 mm respectively. The
defects on test piece from the right side are respectively at 423
Table 2: The Constant parameters maintained for four cases [6] mm and 322 mm. The defect at 423 mm showed porosity due
to improper baking of the welding electrode. The defect at the
Voltage Speed distance of 322 mm is attributed to turbulence in the molten
(volts) (mm/min) pool causing an air entrapment.
GTAW
23 110
(root pass)
SMAW (Ø 4.0 mm) Case 4: In liquid penetration test for the given case no defect
26 110 was seen ensuring the absence of surface defect. In ultrasonic
first pass
SMAW (Ø 5.0 mm) test the intermittent peak is observed at 12.0 mm from the
26 185 bottom and another flaw at 14.8 mm from the bottom. The
subsequent pass
distance of defect is from the right side of the test piece and is
Case 1: A liquid penetration test for the given case showed no located at 175 mm and 280 mm respectively. The defect
defect. The result of ultrasonic test is shown in Figure- 4 where located at 175 mm is introduced due to higher current of the
x-axis represents the depth of specimen and the y axis previous subsequent pass of the SMAW process. The bead
represents the intensity level of the sound signal in dB. The geometry of the weld is not smooth so craters and under cuts
first peak represents the back wall echo from the top of the are generated. These geometric defects not being ground
surface. The intermittent peak at 5.8 mm from the bottom of the correctly at the undercut, the flux has trapped in that under cut
surface shows a flaw. The curve shown in the Figure- 4 is a space. The defect at the 280 mm is attributed to faster cooling
limiting line crossing which the defect can be considered rate.
critical and as the peak is crossing the defect it is considered
critical. The distance of defect is located at 100 mm from the
right side which is introduced due to the wind flow of the 2) Influence of the speed
environment. The wind flow has caused the rupture of Welding speed is the next parameter studied to understand the
shielding gas and caused air entrapment in the molten metal. influence of it on welding defects. Welding speed is varied
keeping welding current, gas-flow rate and arc voltage as
constant.
The parametric details of experiment are shown in Table 3 and
constant parameters are shown in Table 4 respectively. As per
welding procedure [2, 6] and design of experiments carried out
in the present case the welding speed is varied for root pass
weld by GTAW in the range of 56 to 98 mm/min. The first pass
of weld by SMAW is varied from 64 to 112 mm/min. All the
subsequent pass of welding is carried out in the range of 130 to
172 mm/min.
Figure 4 Ultrasonic test for case I [6]
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
Table 3 Variation of Welding speeds for five cases [6] ultrasonic testing has shown no defect. It is thus eminent that
the welding speed selected for the case has not contributed to
Welding speed in Defect location in welding defects.
mm/min mm
Process GTAW SMAW Case 3: The result of this test piece has shown minor defect in
st
Case ROOT 1 Filling the dye penetration test on the surface of the test piece. The
pass pass pass distances of defects in length of test piece from the right side is
Case 1 56 64 130 15 mm,13.8 mm & located at 400 mm and 450 mm respectively. The defects at the
13.4 mm from top distances of 400 mm and 450 mm are introduced due to the re-
surface (UT) striking of the GTAW. The present welding speed selected for
Case 2 70 75 135 110 mm & 150 mm the case also has not contributed to any welding defects.
from right (LPT)
Case 3 80 95 157 400 mm & 450 mm Case 4: The result of this test piece shows minor defect in the
from right (LPT) dye penetration test on the surface of the test piece. The
Case 4 90 105 164 125 mm from right distance of defect in length of test piece from the right side is at
(LPT) 125 mm. The improper grinding of the weld surface has
Case 5 98 112 172 75 mm from right resulted into impregnation of grinding wheel particles as
(LPT) observed in the weld cut cross section. Thus the present
welding speed selected for the case has not caused any welding
defects.
Table -4 The constant parameters maintained for five cases [6]
Case 5: The result of this test piece shows minor defect in the
dye penetration test on the surface of the test piece. The
distance of defect in length of test piece is from the right side at
Current
Voltage (volt) 75 mm. The defect in dye penetrant test at the distance of 75
(ampere)
mm is introduced due to improper cleaning. While testing the
GTAW
150 23 same weld joint by the ultrasonic testing no defect is found in
(root pass)
the test. This clearly indicates that the welding speed selected
SMAW (Ø 4.0 mm)
180 25 for the given case has no influence on welding defects.
first pass
SMAW (Ø 5.0 mm) VI. RESULT AND CONCLUSION
205 25
subsequent pass
The experimental investigations carried out to understand the
influence of welding parameters on weld defects are
Case 1: The result of this test piece shows a few defects in the summarized below:
dye penetration test on the surface of the test piece. The result
of ultrasonic test has shown a defect from left side located at 15
Variation in Welding Current
mm, 13.8 mm and 13.4 mm from the top of the plate. The
The welding current specified in case II (140 amps for
distances of defects in length of test piece from the right side of
GTAW, 140 to 150 for 4.00 mm diameter of SMAW
the test piece are 100 mm, 325 mm and 450 mm respectively.
electrode and 190 amps to 210 amps for 5.00 mm diameter
The defect at the distance of 100 mm is introduced due to
of SMAW electrode) is recommended for quality weld.
striking and re-striking of electrode. The length of arc not being
maintained has resulted into entrapment of gases that has found
Variation in Weld Speed
its way through the ruptured shielded zone. The defect at the
325 mm is introduced due to higher wind flow that was noticed The defects found in ultrasonic testing at 13.0 mm to 15 mm
from the top surface of test piece at lower welding speed in
at the operational level. The defect at 450 mm is introduced due
case I ( 56 mm/min for GTAW, 64 mm/min for the 4.0 mm
to improper cleaning of the surface after welding. The weld
diameter and 130 mm/min for 5.0 mm diameter electrode
joint was not properly cleaned and the cut cross section reveals
for SMAW).
the slag locked in undercut formed due to higher heat input
(low welding speed). The welding speed considered in case II to V could not
show weld defect except surface cracks and hence speed
Case 2: The result of this test piece shows hair line crack on the adopted in case II to V are recommended for quality welds.
surface in the dye penetration test. The distance of the defects The higher welding current causes higher heat input and thus
along the length of a test piece located from the right side of the this results in undercuts and defects. Alsi it is concluded that
test piece are respectively 110 mm and 150 mm. The defect at the lower welding speed should not be used as it has caused
the distance of 110 mm is introduced due to improper grinding higher heat input and this has resulted into undercut and a
as grinding particles were impregnated. The defect at the probability of slag retention.
distance of 150 mm is introduced due to uncontrolled arc
length, as the process is manual. The weld joint tested by the
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
VII. REFERENCES
[1] Boiler and Pressure Vessel Design Code: 2007, ASME
Section VIII, Division 1, ASME Publication, 2007.
[2] Welding and Brazing Qualification, ASME Section
IX: 2007, ASME Publication, 2007.
[3] Dr. R.S. Parmar, Welding Process and Technology,
Khanna Publisher, New Delhi, 2008.
[4] Non Destructive Examination, ASME Section V: 2007,
ASME Publication, 2007.
[5] Baldevraj, C. V. Subramanian, T. Jaykumar,
Non-Destructive Testing of Weld, Woodhead
Publishing, March 2000.
[6] Dissertation report on “Defect Analysis in Dish End
and Nozzle Joint of Glass Lined Reactor”, Sardar Patel
University, Y. R. Rana, H.V. Suthar, 2008.
[7] V. M. Radhakrishan, Welding technology and design,
New age international, New Delhi.
[8] John P. Stewart, The Welder’s Hand book, Reston Pub
Co. 1981.
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
