xa0055847 - osti.gov
TRANSCRIPT
No. 37
1
Gas Metal Arc Narrow-Gap Welding of Pressure Vessels
Made from the Nickel Alloy 2.4663
IllXA0055847
by K. Iversen and A. Palussek
1. Introduction
The highly heat-resistant nickel alloy 2.4663 is used
for the construction of test components of the nuclear
heat reactor PUP as structural material. This material
is given preference for strength reasons in particular
in the range of peak temperatures of 950 °C at pressures
up to 40 bar.
Since no construction and operation experience is yet
available with primary components for the process heat
reactor, test components shall be developed, manu-
factured, and tested. These works are sponsered by the
German Minister of Virtschaft, Mittelstand und Verkehr
of the state of Nordrhein-Westfalen. With the
helium intermediate heat exchanger, two 10 MW types
come under consideration, these being the helical tube
and the straight tube versions. The hot gas collector
component part places the highest demands on the wel-
ding and testing technology. Workpieces of 1000 mm
diameter and wall thicknesses of 42 to 100 mm are to
be forged from material 2.4663, to be joined together,
to be nondestructively tested and to be tested in a
largescale test plant under operating conditions.
2. Design and materials of a hot gas collector test model
Before the construction of the two 10 MW heat ex-
changers, a hot gas collector model shortened in the
longitudinal direction with original wall thicknesses
and diameters was manufactured amongst other things
for the development of the manufacturing technology,
in order to gather in good time experience for the
construction of the components.
Figure 1 shows the design of the hot gas collector
model. Three welds are to be made in the wall thickness
range between 35 - 70 mm. The nickel alloy 2.4663 was
selected as base material and filler wire of the same
composition 1.2 mm diameter was chosen.
Table 1 shows the chemical analyses of base metal, filler
wire and welded joint.
All figures had been within the standards. The burn-out
of the elements aluminum and titanium amounted to 0,19 %•
Therefore limitations of titanium and aluminum to £1,5 %
from the point of embrittlement of the deposited metal
is not necessary according to the latest experiences.
Maximum values of Ti + Al ~ 1#9 % (Al max 1.3 % and
Ti max 0#6 %) were permitted.
3. Welding and testing the hot gas collector model
3.1 Selection of the suitable welding process for the
manufacture_of_the_circular_welds
The manufacture of pressure vessels for the reactor con-
struction necessitates the use of proven reliable welding
procedures. However, with the selection of the welding
procedure neither tested electrodes nor powder for sub-
merged arc have been available for the material 2.4663*
Experience had been gained only for the manual arc wel-
ding processes TIG and GMA each with argon as shielding
gas.
Other welding procedures with high deposition rates like
electro-slag and submerged-arc process could not be used
by means of their hot cracking sensivity caused by the
high heat input. On the other hand efficieny must be an
extremely important point of view if new components are
to be developed. Therefore the decision was made to chose
narrow gap welding with an inert gas.
With expensive base metals and filler wire as well as
high labour costs, the gap width and the side wall angle
effect decisively the quantity of the weld metal to be
filled in, the melting rate and the manufacturing costs.
This applies in particular with larger wall thicknesses,
Fig. 2. According to experience made so far with the nickel
alloy 2.4663, however, the intermediate layer temperature
should be limited to 150 °C, the weld pool size should be
small and overheating of the weld puddle should be
avoided. This led to the selection of a GKA process with
a melting rate of maximum 3 - 5 kg/h. Therefore orLJ-y
single wire processes came into consideration.
For reasons including experience available with pressure
vessels in Japan, the Babcock-Hitachi oscillation flap
process was chosen /~1_7. Fig. 3 and 4 shows the method
of process operation C^.J\ f^bj*
3.2 Qualification 2£_i^£_£§§_S®5ai_§£c_Ba£r!2HzS§2 E£°£eSS
Unfortunately no experience was available for the pro-
duction of circular welds on forged shells of the nickel
alloy 2.4663 with the above-mentioned narrow-gap process.
The same applied for stainless Cr-Ni steels too. There-
fore suitability for welding had to be proven and the
first parameters had to be found with plate samples of
s » 60 mm by fundamental research at the ISF in Aachen/~4^7-
Here it was demonstrated that neither the commercially
used gas mixture of 82 % Ar/18 % COp nor pure argon came
into consideration because of the high arc length and the
too small side wall penetration, Fig. 5« Only the use of
pure helium (99*995 °/°) in combination with the pulse
technique led to a short arc and to a low risk of burn-
back as well as to reduced spattering in the 9 - 11 mm
wide gap. The side wall penetration could be increased
decisively from approx. 0.5 nua to>1 mm and produced
sound welds, Fig. 6.
The low density of the helium had a disadvantageous effect
in the narrow gap because of amongst other things the
formation of very adhesive titanium, aluminum and chromium
oxides on the layer surfaces which could only be removed
by grinding.
At the welding equipment itself, the wire feed system
above all had to be adapted to the significantly stiffer
nickel wire (2.-4-663). The tests in the ISF in Aachen were
concluded successfully after the above-mentioned improve-
ments C^l' The plate samples had to be provided with
an angle of 18° out of the flat for the start of welding
by means of shrinkage.
The continuation of the tests at Interatom took place
initially on circular seams 1000 mm o.d. x 125 mm wall
thickness of 2.4-663. For this the ISF welding data were
taken over and the welding system was completed appro-
priately, Fig. 7. However, because of the impeded
shrinking, heat cracking occurred in the center of the
weld. Only by reducing the layer height, the heat
absorption, the weld pool overheating and the weld pool
size welds could be done successfully without cracks.
Before the optimum data were achieved, single pores and
lack of fusion were found by means of radiographic and
ultrasonic testing. The first circular weld was followed
by the german official TuY process inspection with the
same dimensions.
The root path had been welded manually from the inside
while fillet and the final runs had been welded from the
outside automatically by the narrow gap G-MA process.
For the manual weld Nicrofer S 5520 of 2,4- mm 0 was used
while the automatic GMA process consumed Nicrofer S 5520
wire of 1,2 mm 0 diameter.
All welds had been done in the horizontal position while
the workpiece was turned and the torch was stable. The
opening of the weld preparation was app. 2° to avoid the
squeezing of weld head which was just 7 mm in width by means
of transverse shrinkage, Fig. 8. The opening of the root
srf
gap on the surface was app. 17,8 mm before welding and
lowered down according picture 8 to app. 14 mm before
welding the last path, Fig. 9. The narrow gap welding
with the Babcock-Hitachi-Process is capable of one path
per layer for a gap of 9 - 15 mm and two pathes per layer
till 18 mm.
During this inspection, influences on the welding results
such as not grinding the bead surfaces, welding over of
start and stop points, working out and filling in local
repair places in seam depth and seam width were also tried.
It was shown that welding over ungrinded layers led to
cracks and lack of fusion. All filling layers and the
repair simulations met the required values for BS
according to DIN 8563> Part J. For tbis, however, all
parameters had to be matched exactly to one another and
kept within a close tolerance band. The computer-assisted
welding data monitoring system was here of outstanding
benefit.
After completion of the test weld (81 layers) it was
x-rayed by a linear accelerator. An evaluation of the
films did not lead to a conclusion about weld quality.
It must be stated that good results can be obtained
til 80 mm wall thickness only. The evaluation of the
ultrasonic testing, manually as well as automatically,
Fig. 10, did not show any defect outside tolerance
band. The dye check did not show any defects too.
According to the fixed plan of specimen the forged ring
had to be split up. Six cross sections had to be
examined by TtJV while another 39 had been studied by
INTERATOM. Macro sections did not show any defects
without some minor pores, Fig. 11. Micro sections
(v » 50 or 100:1) did show layers according to speci-
fication but with the exception of some lower area,
where the layers had not been grinded.
In that ungrinded and unsound area lack of fusion as
well as porosity had to "be stated. Most of these defects
had been detected already during x-ray and ultrasonic
testing. The figures of the other testing procedures
are given in table 2.
- £ound_tensile S2ecimen_according_to_DIN_50125
The requirements for the base metal values of Em 2"
700 N/mm2 and Ep 0,2 - 300 N/mm2 were met extremely
close because the lowest value was 302 N/mm . On the
other hand the values of the deposited metal (4-23 N/mm )
as well as the welded Joint (486 N/mm ) exceeded the
specification by far.
The requirements for the yield point had been exceeded
with Ep 0,2 = 328 N/mm but the figures for the ulti-
mate tensile strength did not meet the requirements.
The rupture had been secured in the base metal beyond
the joint. Therefore the weld had met the requirements.
former - 0 : 3 x wall thickness
The following specimen had been taken:
" out of a repaired section bend test specimen
had been taken two for root bend testing and
another two for final layer bend test
* four bend test specimen (two of each for root bend
test and final layer bend test) had been taken from
all around the weld. All specimen did show 180
bend angle without any cracks.
7
notched tar_impact_test_according to_DIN 50115
The specimen had been taken from a place of repair
and from other areas all around the joint. The
requirements of - 40 J was met by all specimen. The
lowest value was shown with 71 J at the weld edge
while the highest was shown with 151 J in the deposited
metal. It can be emphasized that narrow-gap-welds do
show much better results than there is the demand
according to HP 2/1.
With these results the process qualification for the
narrow .gap welding with the single wire snake-wave
process (VP 70) was successfully finished.
According to Fig. 1 three circular seams of different
wall thicknesses (35? 42 and 70 mm) had to be produced.
Narrow-gap welding took place with the welding data proven
in the above-mentioned process inspection. About JO layers
were required for the 70 mm wall thickness, this meant an
average layer height of 2.*? mm. The heat input was 14 kJ/cm,
the welding speed 30 cm/min and the melting rate app.3»8 kg/h.
Radiographic inspections were carried out after about
4-0 mm of weld metal and after laying the final layer
(70 mm). The results of the radiation testing and the
results of the manual as well as computerassisted
mechanized ultrasonic testing, Fig. 9 did show good
harmony.
With the exception of some single pores neither lack
of fusion nor cracks had been detected. After finishing
of the welds (T) and (2) the workpiece had to be oval
shaped followed by welding (seam (^) ) to the bottom,
figure 12.
Fig. 13 shows the figures of transverse and longitudinal
shrinkage depending on wall thickness.
8
4. Summary
The GMA narrow-gap welding process with helium as
shielding gas showed circular welds free of defects up
to s = 126 mm with the nickel alloy 2.4663. The commer-
cially available pulse power source had to be modified at
the shielding gas supply and the wire feed. The selection
of the welding parameters had particular significance. It
was shown that with shrinking-impeded welding of the
circular welds, an overheated weld pool must absolutely
be avoided and that a small weld pool size must be main-
tained. The nickel alloy 2.4663 which contains aluminum
and titanium necessitates grinding of the single layer
surfaces.
However, it remains for the future to show with further
applications if a technical breakthrough of the narrow-
gap welding process with the manufacture of thick-walled
pressure vessels of stainless Cr-Ni steels and nickel
alloys can been made.
5. References
/""1J7 S.Swada, K.Hori, M.Kawahara, M.Takao, I.Asano;
Application of Narrow-Gap Welding Process;
AVS 60th Annual Meeting, 5 April 1979
</"~2 7 C.Ferling; Gas metal arc narrow-gap welding,
a new technology for joining thick plates;
study project of the ISP Aachen, Jan. 1981
/"~3 7 K. Iversen; Review of the process of narrow-gap
welding; Colloquium narrow-gap welding
SLV Duisburg, June 1982
/~4_7 P. Eichhorn, P.Groger; Gas metal arc narrow-gap
welding tests on austenitic chrome-nickel steels
and nickel based alloys; DVS report Vol. 75, 1982
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Properties of Base Metal, Filler Metal andWelded Joints (Narrow Gap )
weld (1
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Fig. Hot gas collector
T3
6
Y=[b-S+2sZ^H)x length
20 40 50 30 100 120 140 160 *80 200 220 thickness [mm]
Fig: 2 Seam volumes as a function of wall thickness and
aoerature anale
We !<Jinq d)tec ft o n
Fig.3 Process with oscillating flap - a) Flap plate
b) Feed rollers
c) Contact nozzle
d) Upper gas protection
e) Welding gap
f) Wire electrode
g) Water cooling
h) Front gas protection nozzle
i) Rear gas protection nozzle
input
vD wire feed speed
8 wire deflection
fp oscillation frequency
output
X wave length
Y oscillation
Wire. Def6rsn/r?3
•Jff
Fig. 5 Penetration depending upon type of shielding gasBase metal: X 5 CrNi 18 9
Filler Metal: X 5 CrNi 18 9
The first 6 layers were welded with argon, thefollowing layers with helium
I
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1 Helium
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Fig. 6 Influence of the shielding gas on the arc lengthand side wall penetration
Fig. "$- G'tA narrow gap welding equipment
81 pathesMIG -Narrow Gap
mTIG ( 2 p a t h e s )
Wsld preparation for MIG-Narrow-Gap
Groove widthon vesselsurface
[mm]
50 60 70 80 125Welded thickness [mm]
Shrinkage of MIG-(Narrow- Gap)-Welding
Fig 1o Fully mechanized ultra-sonic testing of the hot gascollector with computer evaluation
Fig. 44 Narrow gap weld (wall thickness 12^ nun)
Fig 72, H o t <3as collector with 3 circular welds
Transverseshrinkage
Longitudinalshrinkage
125 [mm]wall thickness
a Longitudinal and transverseshrinkage depending onwall thickness