Impermeable Covered Electrode

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:

Everything started with underwater welding projects with CSM - USA and UCLV-CIS – Cuba

We were studying different electrodes

There was a problem!!!

An electrode varnish sample was forgotten.

In a trip to Cuba

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!!

However this motivated a new project to evaluate the varnish influence on:

• Water resistance

• Weldability

• Weld metal microstructure

Covered electrodes for underwater wet welding – varnish evaluation.

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

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

Absorbed water X Time

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)

The welding tests were made using a tank...

and a gravitational welding device.

Covered electrode tips

N V M P S

Polystyrene (N) vinyllic(V) MaritimeTM (M) Polyurethane (P) No varnish (S)

F W +

F W +F P

+

F P+

500x

100x

500x

polystyrene (N)

Weld metalmicrostructure

F W +

F W +

F P+

F P+

500x

500x

100x

vinyllic (V)

F P +

F W +

F W +

F P +

500x

500x

100x

MaritimeTM (M)

polyurethane (P)

F W +

F W +

F P+

F P+

100x

500x

500x

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.

An important question after this project:

Can the varnish be used as binder to substitute the silicate and also

promote protection against water?

N V M PS

In fact tests were made simultaneously with others.

Electrodes manufacture device

N V M PS

Covered electrode tips

The microstructures were compared...

Typical E6013 for underwater wet welding (x1000)

Water depth: 0,5 meters

Polystyrene as binder

F P+

100x

500x

500x

Looks like we found AF microestuture

Impermeable covered electrode for underwater wet welding.

New project started. Now with a company support.

The traditional covered electrode production.

Impermeable covered electrode for underwater wet welding

A comparison between the traditional and the new production processes

Covered electrode for underwater wet weldingE6013 class


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.


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.


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).


The initial tests with different polymer solutions were made in a Lab extruder.


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:


Covered electrodes made with polymer 1


Covered electrodes made with polymer 2


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.



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.




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.


Second stage

• Make covered electrodes on the industrial extruder;

• Evaluate the electrode extrudability;

• Evaluate the covered electrode water resistance;

• Evaluate covered electrode weldability.



Extrudability evaluation:

E6013

E6013


Water absorption evaluation:

Standard E6013

Impermeable

Water depth: 20 meters

The welding tests were made using a tank...

and a gravitational welding device.

Welding parameters evaluation


FA

FPFP

Test 7Polarity: DCEN; Electrode angle: 70°; Welding current: 150 A; Nital 2%; 100X

Magnification: 500X

Electrode P1

Weld bead microstructure


Very strong arc

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


P2P3

P5P6

P1

P2

P3



P4

P5

P6



Electrode Polymer/dry mix

Celulose Potassium silicate

Covering diameter

P1 4.04% 7% 1 5 mmP7 4.07% 7% 1 6 mm

Formulation changes


P1

Welding parameters evaluation


Test 11Polarity: DCEN; Electrode angle: 70°; Welding current: 160 A; Nital 2%; 100X

500X

Electrode P7



The welding tests were then made using a pressure vase...

and a welding device.


Depth: 20 meters


Welding tests

Depth: 20 metrosAmperage: 180A

macro



Depth: 20 metrosAmperage: 200A




Additional tests

Diffusible hydrogen:(Depth: 0.5 meters)

80 ml/100grams of weld metal

The most comercial electrode presents 90 ml/100grams


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.


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?

Development of a low hydrogen impermeable covered electrode for structural welding.

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

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.



Electrodes production in lab.

B1

Standard


Industrial production flow: comparison between the traditional and new processes.


Electrodes production in industry – Same formulation B1 produced in lab.

B2


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

Extrudability evaluation:


B9 formula



Welding tests:


Microstructure evaluation


Microstructure evaluation



Quantitative acicular ferrite evaluation


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


Going on...

Diffusible hydrogen evaluation (Covered electrodes storage under several conditions).Preliminary tests showed good results.

Next steps...

Mechanical properties evaluation.

And the scientific research must go on...

Gracias.Thank you.

Muito obrigado.

Documents

Impermeable Covered Electrode