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Impermeable Covered Electrode
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Impermeable covered electrodesAlexandre Queiroz Bracarense, PhD -
UFMGEzequiel Caires Pereira Pessoa, Dr - UFMGIvanilza Felizardo, Dr - UFMGCláudio Turani Vaz, MsC - UFMGJuliano dos Santos Becho - UFMGGustavo Santiago Hugo - UFMGLorenzo Perdomo Gonzalez, Dr - UCLV – CISManuel Rodriguez Perez, Dr. - UCLV - CISAurecyl Dalla – ELBRAS Ltda
Team members:
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Everything started with underwater welding projects with CSM - USA and UCLV-CIS – Cuba
We were studying different electrodes
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There was a problem!!!
An electrode varnish sample was forgotten.
In a trip to Cuba
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However the cubans had solved the problem!!!They developed a cheap varnish – Expanded polystyrene (Styrofoam™) dissolved in chloroform.
And we did the experiments we had to do!!
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However this motivated a new project to evaluate the varnish influence on:
• Water resistance
• Weldability
• Weld metal microstructure
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Covered electrodes for underwater wet welding – varnish evaluation.
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Covered electrode:
AWS A5.1 E6013, diameter 4,0 mm
Varnish tested:
• Vinyllic (V) – Approved by PETROBRAS• Polystyrene (N) – Cuban development• MaritimeTM (M)• Polyurethane (P)
No varnish (S) also was tested.
Comercial
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Water absortion test
Time(min.)
Electrode mass (Grams)
N 1.1 N 1.2 N 1.3 V 2.1 V 2.2 V 2.3 M 3.1 M 3.2 M 3.3 P 4.1 P 4.2 P 4.3 S 5.1 S 5.2 S 5.3
0 43,623
43,460
43,421
43,780
43,974
43,730
43,773
43,682
43,722
43,823
43,701
43,651
43,359
43,367
43,338
5 43,751
43,544
43,516
43,818
43,996
43,774
43,817
43,741
43,782
43,825
43,715
43,658
43,987
43,035
43,967
15 43,868
43,643
43,620
43,860
44,038
43,794
43,903
43,852
43,842
43,826
43,767
43,661
44,061
44,082
44,059
30 44,016
43,819
43,788
44,045
44,142
43,811
44,054
44,027
43,924
43,874
43,834
43,736
44,094
44,095
44,093
60 44,186
44,070
44,023
44,146
44,013
43,975
43,687
120 44,515
44,331
44,328
44,471
44,513
240 44,649
44,407
44,413
480 44,777
44,523
44,482
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Absorbed water X Time
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N – 2 hours
V – 30 min.
M – 30 min.
P – 1 hour
S – 30 min.
Covered electrode after water absorption test
Polystyrene (N) Vinyllic(V) MaritimeTM (M) Polyurethane (P) No varnish (S)
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The welding tests were made using a tank...
and a gravitational welding device.
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Covered electrode tips
N V M P S
Polystyrene (N) vinyllic(V) MaritimeTM (M) Polyurethane (P) No varnish (S)
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F W +
F W +F P
+
F P+
500x
100x
500x
polystyrene (N)
Weld metalmicrostructure
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F W +
F W +
F P+
F P+
500x
500x
100x
vinyllic (V)
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F P +
F W +
F W +
F P +
500x
500x
100x
MaritimeTM (M)
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polyurethane (P)
F W +
F W +
F P+
F P+
100x
500x
500x
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Conclusions:
Despite the higher water absorption during the first 30 minutes, the polystyrene varnish guarantees the best water resistance.
There are no morphological differences in the weld metal produced with E6013 covered electrodes coated with the different varnish. All the samples showed primary and Widmanstätten ferrite. The presence of other types of ferrite, like polygonal and acicular, was insignificant.
The results obtained with some varnish showed that they can be successfully used in this application.
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An important question after this project:
Can the varnish be used as binder to substitute the silicate and also
promote protection against water?
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N V M PS
In fact tests were made simultaneously with others.
Electrodes manufacture device
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N V M PS
Covered electrode tips
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The microstructures were compared...
Typical E6013 for underwater wet welding (x1000)
Water depth: 0,5 meters
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Polystyrene as binder
F P+
100x
500x
500x
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Looks like we found AF microestuture
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Impermeable covered electrode for underwater wet welding.
New project started. Now with a company support.
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The traditional covered electrode production.
Impermeable covered electrode for underwater wet welding
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A comparison between the traditional and the new production processes
Covered electrode for underwater wet weldingE6013 class
Impermeable covered electrode for underwater wet welding
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Goals:
• Develop a commercial impermeable covered electrode to be used on the underwater wet welding.• Evaluate the polymer influence on the weld metal structure and properties.
Start point:
• AWS A5.1 E6013 was the base formula.
Impermeable covered electrode for underwater wet welding
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Methodology
This project was developed in two stages:
First stage:
Make covered electrodes on the Lab to evaluate the water resistance and extrudability.
Second stage:
Make covered electrodes in an industrial plant to evaluate the extrudability and weldability.
Impermeable covered electrode for underwater wet welding
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First stage
• Make covered electrodes with different polymer solutions on the Lab extruder;
• Evaluate the electrode extrudability (preliminary evaluation);
• Evaluate the covered electrode water resistance;
• Evaluate covered electrode weldability (preliminary evaluation).
Impermeable covered electrode for underwater wet welding
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The initial tests with different polymer solutions were made in a Lab extruder.
Impermeable covered electrode for underwater wet welding
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Solvent/polymer Polymer/dry mix
Polymer 1
11.07 0.04
Polymer 2
3.5 0.06
The best water absortion test result was obtained with the relations below:
Impermeable covered electrode for underwater wet welding
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Covered electrodes made with polymer 1
Impermeable covered electrode for underwater wet welding
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Covered electrodes made with polymer 2
Impermeable covered electrode for underwater wet welding
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Parâmetros de fabricação dos eletrodos% of plastic in the
flux mass (g) plastic (g) solvente (g) mass/solution Solvente/plastic
2 30 0.6 13.19 2.18 21.984 25 1 11.23 2.04 11.236 30 1.8 13.16 2.01 7.318 30 2.4 13.08 1.94 5.4510 30 3 12.96 1.88 4.32
% of plastic in the flux
Massinicial Massfinal Mass % of absorved water in 30min
Average % of absorved water
4*10.2839 10.2952 0.0113 0.1099
0.1099
610.5896 10.6019 0.0123 0.1162
0.103710.4195 10.4290 0.0095 0.0912
810.6604 10.6701 0.0097 0.0910
0.087610.2184 10.2270 0.0086 0.0842
1010.1316 10.1406 0.0090 0.0888
0.091610.3810 10.3908 0.0098 0.0944
Water absorption test: polymer 1
* The lowest polymer quantity was 4%. Covered electrodes made with 2% polymer dissolved when in contact with water.
Impermeable covered electrode for underwater wet welding
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Impermeable covered electrode for underwater wet welding
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Parâmetros de fabricação dos eletrodos% of plastic in the
fluxMass
(g) Plastic (g) Solvente (g) mass/solution Solvente/plastic
2 25.00 0.50 6.29 3.68 12.584 16.42 0.66 3.30 4.15 5.006 21.38 1.28 3.85 4.17 3.008 20.75 1.66 4.15 3.57 2.510 25.00 2.5 5.68 3.06 2.27
% of plastic in the flux
Massinicial Massfinal Mass % of absorved water in 30min
Average % of absorved water
4*10.5386 10.5506 0.0120 0.1139
0.110710.6903 10.7018 0.0115 0.1076
610.3015 10.3138 0.0123 0.1194
0.122810.4571 10.4703 0.0132 0.1262
810.3608 10.3740 0.0132 0.1274
0.127810.6026 10.6162 0.0136 0.1283
1010.4401 10.4478 0.0077 0.0738
0.082310.5658 10.5754 0.0096 0.0909
Water absorption test: polymer 2
* The lowest polymer quantity was 4%. Covered electrodes made with 2% polymer dissolved when in contact with water.
Impermeable covered electrode for underwater wet welding
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Impermeable covered electrode for underwater wet welding
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Impermeable covered electrode for underwater wet welding
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Conclusions
• Even though the difference is very small, we decide to use Polymer 2 in the next experiments.
•The solvent used with Polymer 2 stayed longer, what was good for the extrudability.
Impermeable covered electrode for underwater wet welding
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Second stage
• Make covered electrodes on the industrial extruder;
• Evaluate the electrode extrudability;
• Evaluate the covered electrode water resistance;
• Evaluate covered electrode weldability.
Impermeable covered electrode for underwater wet welding
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Impermeable covered electrode for underwater wet welding
Extrudability evaluation:
E6013
E6013
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Impermeable covered electrode for underwater wet welding
Water absorption evaluation:
Standard E6013
Impermeable
Water depth: 20 meters
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The welding tests were made using a tank...
and a gravitational welding device.
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Welding parameters evaluation
Impermeable covered electrode for underwater wet welding
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FA
FPFP
Test 7Polarity: DCEN; Electrode angle: 70°; Welding current: 150 A; Nital 2%; 100X
Magnification: 500X
Electrode P1
Weld bead microstructure
Impermeable covered electrode for underwater wet welding
Very strong arc
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P1
P4
Electrode Polymer/dry mix
Celulose Potassium silicate
Covering diameter
P1 4,04% 7% 1 5 mmP2 2,51% 0% 1 5 mmP3 3,92% 0% 2 5 mmP4 3,92% 7% 2 5 mmP5 3,92% 7% 3 5 mmP6 6,92% 4% 2 6 mm
Formulation changes
Impermeable covered electrode for underwater wet welding
P2P3
P5P6
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P1
P2
P3
Impermeable covered electrode for underwater wet welding
Weld bead microstructure
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P4
P5
P6
Impermeable covered electrode for underwater wet welding
Weld bead microstructure
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Electrode Polymer/dry mix
Celulose Potassium silicate
Covering diameter
P1 4.04% 7% 1 5 mmP7 4.07% 7% 1 6 mm
Formulation changes
Impermeable covered electrode for underwater wet welding
P1
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Welding parameters evaluation
Impermeable covered electrode for underwater wet welding
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Test 11Polarity: DCEN; Electrode angle: 70°; Welding current: 160 A; Nital 2%; 100X
500X
Electrode P7
Weld bead microstructure
Impermeable covered electrode for underwater wet welding
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The welding tests were then made using a pressure vase...
and a welding device.
Impermeable covered electrode for underwater wet welding
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Depth: 20 meters
Impermeable covered electrode for underwater wet welding
Welding tests
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Depth: 20 metrosAmperage: 180A
macro
Impermeable covered electrode for underwater wet welding
Weld bead microstructure
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Depth: 20 metrosAmperage: 200A
Impermeable covered electrode for underwater wet welding
Weld bead microstructure
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Impermeable covered electrode for underwater wet welding
Additional tests
Diffusible hydrogen:(Depth: 0.5 meters)
80 ml/100grams of weld metal
The most comercial electrode presents 90 ml/100grams
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Impermeable covered electrode for underwater wet welding
And the project goes on...
Groove welding at 20 meters.
Welded joint and weld metal mechanical properties evaluation:
• Tensile test;• Bend test;• Hardness test;• Charpy – V notch test.
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Impermeable covered electrode for underwater wet welding
Another important question arrived after this stage:
Can the varnish be used as binder to substitute the silicate for air
welding?Or
Can we develop an impermeable low hydrogen covered electrode
for structural welding?
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Development of a low hydrogen impermeable covered electrode for structural welding.
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Low hydrogen impermeable covered electrode for structural welding.
Goals:
• Develop a commercial low hydrogen impermeable covered electrode for structural welding.• Evaluate the polymer influence on the weld metal structure and properties .
Start point:
• AWS A5.1 E7018 was the base formula
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Project steps:• Covered electrodes lab production to evaluate the extrudability and weldability;• Covered electrodes industrial production;
Results:• Extrudability (production evaluation);• Welding tests;• Microstructure evaluation (including AF evaluation);• Microhardness• Difusible hydrogen tests; • Weld metal mechanical properties.
Low hydrogen impermeable covered electrode for structural welding.
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Low hydrogen impermeable covered electrode for structural welding.
Electrodes production in lab.
B1
Standard
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Low hydrogen impermeable covered electrode for structural welding.
Industrial production flow: comparison between the traditional and new processes.
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Low hydrogen impermeable covered electrode for structural welding.
Electrodes production in industry – Same formulation B1 produced in lab.
B2
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Low hydrogen impermeable covered electrode for structural welding.
Formula
Changes
B3 Limestone rutile fluorspar Improve arc stability and reduce arc power
B4 FeSi FeMn Chemical balanceB5 Hematite + Improve slag formation -
Oxidation B6 FeSi FeMn Chemical balance againB7 Hematite Reduce oxidation even
moreB8 Limestone rutile fluorspar
hematite -Increase arc power
B9 Limestone fluorspar glass + Metal viscosity control
Formulation changes
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Extrudability evaluation:
Low hydrogen impermeable covered electrode for structural welding.
B9 formula
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Low hydrogen impermeable covered electrode for structural welding.
Low hydrogen impermeable covered electrode for structural welding.
Welding tests:
Low hydrogen impermeable covered electrode for structural welding.
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Microstructure evaluation
Low hydrogen impermeable covered electrode for structural welding.
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Microstructure evaluation
Low hydrogen impermeable covered electrode for structural welding.
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Low hydrogen impermeable covered electrode for structural welding.
Quantitative acicular ferrite evaluation
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Low hydrogen impermeable covered electrode for structural welding.
Vickers hardness
Hardness HV100
B9 264 245 245 236 206 228
BABU, S.S., BHADESHIA, H.K.D.H. Transition from Bainite to Acicular Ferrite in Reheated Fe-Cr-C Weld Deposits.Materials Science and Techonology, v.6, p. 1005-1019, 1990.
BABU, S.S., BHADESHIA, H.K.D.H. Mechanism of the Transition from Bainite to Acicular Ferrite. MaterialsTransation, JIM, v.32, n. 8, p. 679-688, 1991.
~ 237 HV
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Low hydrogen impermeable covered electrode for structural welding.
Going on...
Diffusible hydrogen evaluation (Covered electrodes storage under several conditions).Preliminary tests showed good results.
Next steps...
Mechanical properties evaluation.
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And the scientific research must go on...
Gracias.Thank you.
Muito obrigado.