IOFW L

Low HYDROG N. ELECTROD_".

BYM. P. DHANUKA .

GEELimitedKalyan INDIA

LIFELINEOF WELDING

Low HYDROGENELECTRODES

Moisture-resistantE7018 H4R

andE7018-1 H4R

BYM. P. DHANUKA

GEE LimitedKalyan INDIA

GEE Limited

Introduction1.0 Electric arc welding has been in use in industry for a very long time. Because

of its versatility, it appears that this process will dominate the field of joiningmetals and alloys for many more years.

The first steps in electric arc welding were taken by Bernados and Olszewakiin 1885 when they patented a method of welding, using an arc struck betweena carbon electrode and the workpiece. The direct use of a metal-arc electrodewas patented in the U.K. by N. Slavianoff in 1890.

The first reference to a welding application in the 'Journal of theIron & Steel Institute' appears in 1901 and describes the welding of cast ironand wrought iron at Furstenwald near Berlin using the Slavianoff process anda flux of powdered glass plus 1% of ferromanganese.

The first patent for covered electrode was filed in the year 1907 byO. Kjellberg, followed by another patent in the year 1912. Strohmenger in1911 patented an electrode wound with asbestos yarn impregnated withsodium silicate.

The first all-welded barge was launched in June 1918.

The first version of basic type of covered electrode was developed during theearly '30s. The covering of the electrode had a high proportion of lime andfluorspar. In Germany, basic type of electrodes were used during World War IIfor welding of armour plates as an effective substitute for the austenitictypes.

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One of the most successful modern rutile-based general purpose electrodewas first developed in 1941 for Welding in shipyards. It is still one of thelargest selling electrode in most of the countries. During the 30's, 40's and50's, a large number of electrodes was developed depending on applicationrequirements. Based on Flux coating formulations, these electrodes canbe classified broadly as under:

TABLE I

TYPE OF COVERING SFA 5.1 CLASSIFICATIONS

1 Cellulosic coated electrode

2. Acid type -High iron oxide withor without iron powder

3. Rutile, Rutile cellulosic typeelectrode with or withoutIron powder

4. Low hydrogen electrode withor without iron powder in the fluxCoating

5. Iron oxide with titania

E6010,E6011

E6020,E6022E6027,E7027

E6012,E6013,E7014E7024, E7014-1

E6018,E7015,E7016,E7018E7028,E7048, E7016-1E7018-1, E7018-M

E6019

2.0 Achieving high quality welds2.1 Achieving high quality welds is the objective of every fabricator

and it is the basic requirement of his client. Deposited weld metalcan be termed as high quality weld provided the weld metalfulfills the following requirements.

(a) Deposited weld is free from defects.

(b) Deposit.ed weld has required performance.(c) Deposited weld meet required standards and specifications.

2.2 Types of electrodes and mechanical properties of the deposited weldmetal.

Various types of electrodes conforming to respective AWS/SFAclassifications fulfill the code requirements with respect tochemical composition of weld metal, mechanical properties ofweld metal, and usability and soundness test requirements.

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Table 2 gives details of impact test requirements for various types

of electrodes.TABLE 2

AWS / SFA CLASSIFCATION CHARPY V-NOTCH IMPACTREQUIREMENT, MINIMUM

Not specified1.E6012,E6013,E6020,E6022,E7014,E7024

2. E6019,E7028,E7024-1

3.E6010,E6011,E6027,E6018,E7015,E7016,E7018,E7027,E7048

4. E7016-1, E7018-1

5. E7018M

27Jat-20°C

27Jat-30°C

27Jat-45°C

67Jat-30°C

2.3 Hydrogen content of the weld metal and types of electrodes:

Only Low-Hydrogen basic type of electrodes such as E6018, E7015,

E7016, E7018, E7048, E7028, E7016-1, E7018-1 and E7018M have been

designed to deposit weld metal having low levels of hydrogen. Hydrogen

content in the deposited weld metal depends on many factors. These aspects

will be dealt with separately in this paper.

2.4 Hydrogen in the weld metal and susceptibility to cold cracking inferritic welds

2.5 Defects in weldsWeld defects are broadly classified into two types:

A) Defects induced by the welder due to low skills, difficult Workingenvironment etc.

B) .Defects due to the metallurgical characteristics of the material.

Typicalexamples:

'Defects due to welder Defects due toMetallurgical Characteristics

a) Lack of side wall fusionb) Lack of penetrationc) Undercutting at toes

a) Hydrogen crackingb) Solidification crackingc) Lamellar tearing

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2.6 Hydrogen induced cracking in welds

Hydrogen cracking in the weld metal as well as in the parent metal has beenthe subject of intense research for many years. However, it is still the mostcommon defect found in welded structures. The cost of repairs due tohydrogen cracking is, on a worldwide basis, enormous. Traditionally,hydrogen cracking occurs in the hardened coarse grained HAZ region offerritic steels but the advent of low carbon steels has seen a significantincrease in weld metal hydrogen cracking. HAZ Hydrogen cracking occursdue to four factors which are as under:

1) Hydrogen2) Susceptible microstructure in the coarse grained HAZ3) Stress4) Ambient temperature

If anyone of the above factors is removed, then it would be possible to preventthe cracking of the weld metal or HAZ cracking Even though all the 4 factorsmentioned above have equal importance, hydrogen is an elusive elementwhich affects cold cracking susceptibility in ferritic welds. Hence control ofhydrogen in the weld metal is of paramount importance.

3.0 HydrogenHydrogen in the weld metal can be introduced from a number ofsources. The most likely sources are as under:Moisture in the electrode coating or moisture in fluxesMoisture on the steel surfaceWater combined with rust, oils and other greases on the workpiece or filler wireOrganic degreasing agents used for cleaningMoisture present in the atmosphereResidual hydrogen in the steel- especially in thick section Material

In the case of manual metal arc welding, the main source of hydrogen is themoisture contained in the electrode coating. During welding, dissociationoccurs and the atomic hydrogen thus formed dissolves in the molten pool.

During cooling much of the hydrogen escapes from the solidified bead bydiffusion but some quantity diffuses into the HAZ and the parent metal. The

I)II)III)

IV)V)VI)

3.1

3.2

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amount which does so depends on several factors such as the original amountabsorbed, the size of the weld, the decreasing solubility and time temperatureconditions of cooling.

FIG 1Amount of hydrogen absorbedby molten weld pool varies withconcentration in atmosphereSurrounding the arc. Solubilityat 1900°C

FIG 2Solubility of hydrogen inweld metal decreases astemperature falls

,., Liquid FO

v)

VYFe

l;:' aFI

25

Cl810 ~----~--~~----~~E

20Cloo

19Q)

E-0Qi;;: 5 ~---I"~----+-----~.scQ)Cle"§;,I

E 15

~:c::Jo 10(/)

cQ)Clo-6 5>-I

5 10

Hydrogen in arc atmosphere500 1000 1500 2000

Temperature, DC

In general, the more the hydrogen present in the metal, the greater the risk ofcracking".Control over the hydrogen level of the weld metal may be achievedby minimising the amount initially absorbed or by ensuring that sufficienttime is allowed to escape by diffusion before the weld cools. Often acombination of both measures provides the best practical solution.

3.3 Moisture in the Flux coating of electrodes may be present as absorbed

water, loosely combined water of crystallisation or m 0 ref i r m Iy b 0 u n d

molecules in the silicate structure. All these forms can break down to

produce hydrogen.

3.4 Definition of low hydrogen electrodeUnderstanding of the role of diffusible hydrogen in delayed cracking of welds

in carbon steel and low alloy steel came about at least as long ago as the

1940's. Indeed, classification of low-alloy steel electrodes designated as

"Low hydrogen", was introduced into AWS specification A5.5-48T

(ASTMA316-48T) in 1948 along with a diffusible hydrogen test using

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collection of hydrogen from a quenched weld bead over glycerine. The Low

hydrogen electrode was defined as one meeting a maximum limit of 0.1 cubic

centimeter of gas collected per gram of deposited weld metal (10ml/l00g, in

units commonly used today for expressing diffusible hydrogen).

3.5 Shortly after this specification was published, Stern Kalinsky and Fenton cast

doubt on the suitability of collection of hydrogen over glycerine by showing

that collection over mercury produced considerably more hydrogen because

hydrogen is soluble in glycerine. By way of the 1954 revision of AWS 5.5, the

glycerine test was withdrawn from the specification and it was replaced in the

1964 revision by definition of Low-hydrogen, as those having no more than

0.6 percent coating moisture by weight, with lower limits for higher strength

electrode. This definition of Low-hydrogen electrodes in terms of 0.6 percent

coating moisture, became the mandatory section of AWS A5.1 specification

in the 1981 revision.

AWS A5.1 specification, was further revised in the year 1991 and in the year2004. In this specification, diffusible hydrogen test is required for E7018Melectrode, whereas for other Low hydrogen basic coated electrodes, diffusiblehydrogen test is only required when diffusible hydrogen designator is addedto the classification.

For Example:E 7018H4, E 7018H8 and E 7018H16

3.6 As per the new classification system for low hydrogen electrodes the upper

limit for diffusible-hydrogen is 16ml!100g which fits well with the correlation

of 0.6 percent coating moisture. As per AWS/SFA 5.1 specification, diffusible

hydrogen content of the weld metal is to be tested in accordance with

ANSI/AWS A4.3 specification, "Standard methods for Determination of the

diffusible hydrogen content of Martensitic, Bainitic and Ferritic weld metal

produced by Arc welding".

As mentioned above, diffusible hydrogen testing is required asper AWS/SFA5.1 specification for all Low hydrogentype electrodes when

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diffusible hydrogen designator is added to the classification. Diffusiblehydrogen limits for weld metal are given in the following table:

TABLE 3

AWS Diffusible Diffusible hydrogen contentClassification Hydrogen Average MI (H2) /lOOg

Designator Deposited metal, max

E 7018M None 4.0E6018 -

E 7015E7016 H16 16.0E 7016-1E7018 H8 8.0E 7018-1E7028 H4 4.0E7048

4.0 Determination of the diffusiblehydrogen content of the weld metalby mercury method as againstglycerine methodIt was recognised long ago that glycerine dissolves not only some hydrogenbut it dissolves oxygen, nitrogen, carbon dioxide and water M.A. Quintanashowed that, as the glycerine bath aged, the concentration of hydrogen in thegas collected from a diffusible hydrogen test decreases from about 70 percentto about 50 percent As the apparent diffusible hydrogen ofthe test specimenincreased, the concentration of hydrogen in the gas collected over glycerineincreased from about 55% at 6ml!100g to about 75% at about10m 1/1 00 g.The remainder of the gas collected consist of other dissolvedgases which are displaced from glycerine by the dissolved hydrogen.

4.1 At very low hydrogen level, no gas is collected. All of the hydrogendissolves without displacing any other dissolved gases.

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4.2 The Japanese have conducted at least three studies of correlationbetween the glycerine test the IIW method. In the first study, thetest weld was quenched 30 seconds after the arc was extinguished. Thefollowing correlation equation was obtained.

Hjis = 0.64 Hiiw - 0.93 ........ (1)

In the second study, the test weld was quenched 5 seconds after thearc was extinguished.

The Second study provided slightly higherequation is given below:

hydrogen and the

Hjis= 0.67 Hiiw - 0.80 ........ (2)

More recently, the Japanese have moved to adding a run-on andrun-off tab to the test specimen. They produced a third equationwhich is a as under:

Hjis= 0.79Hiiw-1.73 ......... (3)

The three equations are plotted in fig 3 which shows that there isvery little difference among them

FIG3L()~'<t~(")~N~~~0~

Cl0 c»0

E co2!- r--.I'

<0

L()

'<t

(")

N

0

0 2 4

Hgly = 0.64 Hllw - 0.93Hgly = 0.67 Hllw - 0.8Hgly = 0.79 Hllw -1.73

8

6 8 10 12 14 16 18 20

Hllw, ml/100g

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5.0 Correlation between coating moistureand diffusible hydrogen

5.1 In evaluating correlation between coating moisture and diffusible hydrogen,it is important to keep in mind that correlation can not be perfect becauseseveral factors can influence the relationship. Few factors which caninfluence the relationship are as under:

a) At the same coating moisture level, an electrode with a heavycoating would deliver to the arc more hydrogen than would anelectrode with a thin coating;

b) The addition of fluorides to an electrode slag system will causeremoval of some hydrogen. As a result, similar electrodes at the samecoating moisture level, will yield different diffusible hydrogen levels if oneis appreciably higher in fluoride than the other;

HIRAI and co-workers developed a predictable equation whichrelated IIW diffusible hydrogen to as baked coating moisture (a1percent), moisture picked up by exposure (a2 percent) andpartial pressure of water vapour in the air at the time of welding(b, mm ofHg) for E7018 type electrode.

HD- (260al + 30a2 + 0.9b -10) ~ (4)

5.2 For freshly baked electrodes, the exposure term of equation (4)could be zero and atmosphere condition for the welding amountto about 10mm Hg partial pressure of water. Based on the results,correlation between diffusible hydrogen versus coatingmoisture for E7018 is plotted in fig (4)

FIG40> 18aa 16

•20 •

• • •c~ 12e-g 10IOJ:c·00 6:Eo

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Coating Moisture, PercentThe correlation holds good for coating moisture below 03. percent

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"'- --

6.0 Effect of basic coated electrodeexposure on the diffusible hydrogencontent of the weld metalAs-manufactured coating moisture of the basic coated electrode is likely to bemore concentrated in the interior of the coating than on the surface because,in baking the electrode, moisture must diffuse outward through the coatingthickness in order to escape. Conversely, moisture picked-up duringexposure must enter the electrode coating from the outside surface, anddiffuse inwards. This surface moisture could be less tightly bound to thecoating than the as-manufactured moisture which survived a hightemperature baking. In other words, rehydrated moisture picked-up duringexposure will be less effective in introducing diffusible hydrogen into theweld metal than the as-manufactured moisture. Dr. Evans provided theresults of basic coated electrode diffusible hydrogen versus coating moistureon Drying and on exposure which are given in fig 5

FIG5

20

16

Cloo

E 12

4

o0.0 0.4 0.6 0.70.2 0.3 0.50.1

Coating Moisture, PercentDiffusible Hydrogen vs. Coating Moisture on Drying and on Exposure

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7.0 Correlation ofwith cracking

diffusible hydrogen

Evans and Christense and Christense and Simonsen examined the criticalcracking stress by the implant test of a variety of steel as a function ofhydrogen content of the weld metal.

An example of their data is shown in fig 6. This data was obtained from a steelofO.17C, 1.36 Mn. Both rutile and basic coated electrodes were used to obtainvarious hydrogen levels.

FIG 6A FIG 6B

Lo. 5.0 mm electrodeo 4.0 mm electrodeD 3.25 mm electrode

Critical Cracking Stress versus Total Hydrogen,Implant Test of Carbon Steel~ 80 ,-~~--~~~~~~~~---,

g 70

e!U5 60Olc

:52 50oC\lo 40

roo 30

""B 20

80 ~~~~~~~----~--~-,

"(i) 70~en 60C/)e!U5 50

~ 40:;;;:~ 30

oro 20o

:.;::; 10

B10

5 • 10 15 20 25 30 35 3 4 5 6 7 8 10 20 30 40

Total Hydrogen, Ppm Critical Cracking Stress versus Total Hydrogen,Implant Test of Carbon Steel Logarithmic

Hydrogen Axis Total Hydrogen, pgm

The hydrogen levels reported are based upon fused metal (deposited metal plusmelted base metal)

Critical cracking stress is plotted in two ways, directly against hydrogen content ofthe weld metal and against the logarithm of the weld metal hydrogen content via asemi-logarithm plot.

For all steel examined, the critical cracking stress, under otherwise identicalconditions, is a linear function of the logarithm of hydrogen content of the welddeposit. It is not a linear function of the hydrogen content. In particular, a smallchange in hydrogen content is much more important at a low hydrogen levelthan at a higher level.

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At a given preheat temperature, the critical carbon equivalent forcrack-free welding varies as a function of the diffusible hydrogen content of theweld metal. Yurioka conducted experiments on the above lines and his result arereproduced in fig 7 A & 7 B.

FIG. 7 A

0.20

0.15

C 0.10Ql

Cii>'s 0.050-wC0.0

0.00Cii0.sQl

-0.050)cctls:0

-0.10

-0.15

-0.200

FIG. 7 B

0.20

0.15CQl

co> 0.10'::;0-wc 0.050.0Cii0.!: 0.00Ql0)Cctls: -0.050

-0.10

-0.15

-0.20

5 5010 20 2515 30 35 40 45

Diffusible Hydrogen, ml/100gCarbon Equivalent Adjustment

2 3 4 5 6 7 8 10 30 40 5020

Diffusible Hydrogen, ml/100gCarbon Equivalent Adjustment

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8.0 Effect of the atmosphericmoisture during welding on thecontent of diffusible hydrogeninthe weld metalIn most of the arc welding processes including shielded metal arcwelding, the arc is imperfectly shielded from the air, Duringthe welding process, moisture from the atmosphere does enterthe arc and the weld metal.

Ruge and Dickehut developed nomogram for estimating the effectof atmospheric moisture at the time of welding on the weld metaldiffusible hydrogen.The nomogram predicts, for example, that an electrode type E7018, which produces 3.0ml/l00g. diffusible hydrogen whentested at 20°C and 40% relative humidity, will produce5.4ml/l00g. when tested at 30°C and 80% relative humidity, anincrease of 2.4ml/l00g.

But an electrode type E 7018 which produces 9.0ml/l00g. whentested at. 20°C and 40% relative humidity, will produce about10.0rill/l00g. when tested at 30°C and 80% relative humidity, anincrease only of 1.0ml/l00g.

8.2 Following conclusions can be drawn from the various experimentscarried out:

8.1

1) The effect of atmospheric moisture at the time of welding isgreater for very Low or Ultra low hydrogen electrode than it is forhigher hydrogen electrodes.

2) Long arc during welding will have more tendency to pick-upmoisture from the atmosphere and will produce more hydrogenin the weld metal.

3) In GMA and gas-shielded arc welding, drafts or otherdisturbances to the gas shielding can be expected to increasediffusible hydrogen of the weld metal.

4) In self-shielded flux-cored arc welding, high voltage increasesthe arc length and can be expected to increase diffusiblehydrogen.

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9.0 Welding consumables : basic coatedelectrodes

9.1 In order to minimise the risk of cold cracking during welding of carbon steeland low-alloy steels, a lot of developments have taken place during the lastfew decades. Designs of basic coated consumables cover the followingfour aspects:I) Low, very low and extra low level of hydrogen in the weld metalII) Response to redryingIII) Resistance to moisture reabsorption characteristicsIV) Special Packaging.

9.2 By using the most updated in house technology, the mostadvanced extra low hydrogen type of electrodes having thefollowing classifications have been developed.

E7016·E7016-1

E7018E7018-1

These electrodes have the following unmatched properties:

a] The weldability that WELDERSreally enjoy.Recently developed Low-hydrogen basic coated electrode features the besteasy handling characteristics in all positions. The deposited weld metal hasuniform ripples and absolutely no spatter. An end to difficult positionalwelding and lack of fusion on vertical up welding position. These electrodesdeposit x-ray/ radiographic quality welds in all positions including 5G,6Gor6GR

b) The mechanical properties that WELDINGENGINEERSreallyappreciate.Recently developed Low-hydrogen basic coated electrodes guarantee highmechanical. properties in comparison with other non-alloy basic coatedelectrodes. Charpy V-notch impact values are more than 100 joules whentested at -30DC or - 46DC.

c) Extra low-level of Diffusible hydrogen.The flux coating of these electrodes has a unique feature, a barrier to moistureabsorption and diffusible hydrogen to the weld metal. After 9 hrs. of exposureat 27DC at 80% RH, the maximum moisture in the flux coating is 0.20% anddiffusible hydrogen is less than 4ml!100g of the weld metal.

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Fig 8 shows moisture absorption versus exposure time for recently developedE7018 class of electrodes.

FIG 8

0.6

0.5~ 0.4t-zWt- 0.3z0oW0:: 0.2::Jt-(fJ

0 0.1::;;;:

0

------ ---~ ~

.•..

6

5Ola

4a

I3 --'

~W::;;;:

2 0--'W

~1 0

:r:

0o 3 6 9 12 15 18 21 24

Exposure Time (h)

10,0 Moisture-resistant electrodes10.1 Recent years have seen much emphasis on developing coated electrodes

whose coating resist moisture pick-up. Such developments have permittedthe user to test the electrodes for moisture pick-up with a view to extendingthe exposure time permitted by the structural welding code steel and otherfabrication standards.

Moisture-resistant basic coated electrodes in accordance withAWS/SFA 5.1-91 or 5.1-2004 specifications are designated· byadding the suffix letter "R" after the four digit classification number.

As per the specification, a letter "R" is a designator used with theLow-hydrogen electrode classification. The letter "R" is used to identifyelectrodes that have been exposed to a humid environment for a given lengthof time and tested for moisture absorption in addition to the standardmoisture test required for classification of Low-hydrogen electrodes.

As per the specification, "R" designated electrodes are exposed to anenvironment of 26.7°C (80°F) and 80% relative humidity for a period of notless than 9 hours by any suitable method. The moisture content of theelectrode covering is then determined by any recommended method. Themoisture content of the exposed covering should not exceed 0.40%,maximum specified moistur content for the electrode.

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10.2 Diffusible hydrogen testIn addition to the absorbed moisture test, the basic coated lowhydrogen electrode designated by an optimal supplementaldiffusible hydrogen designator are tested according to one of themethods given in ANSI/AWS A4.3 Standard Methods forDertermination of the diffusible Hydrogen content of Martensitic,Bainitic and Ferritic steel weld metal.

For the purpose of certifying compliance with diffusible hydrogenrequirements, the reference atmospheric condition shall be an absolutehumidity of 10 grains of water vapour per pound (1.43g/kg) of dry air at thetime of welding. The actual atmospheric conditions is to be reported alongwith the average values for the test according to ANS/AWS A4.3-86specification.

Two types of analytical apparatus are used for analysis of diffusiblehydrogen.

(I) Mecury filled eudiometer

(II)GAS chromatography

The test specimen confined within its isolation chamber is held at thehydrogen evaluation temperature as per the following details.

TABLE4

Minimum hydrogen diffusible times at acceptable temperatures

Diffusion temperature, c (f)

+ 3°e +5°F

Minimum diffusion time hrs

(113)(302)

726

45150

Metallic mercury and vapours are hazardous and can be absorbed into thebody by inhalation, ingestion or contact with the skin. Therefore allprecautions involving the handling of mercury should be observed duringmeasuring hydrogen by the mercury method.

On the, other hand, gas chromatography procedure is quite safe and is used bymany European and Japanese manufacturers of basic coated Low-hydrogenelectrodes. Since gas chromatography procedures vary from instrument toinstrument, it is necessary to study carefully 'the instruction and

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calibration procedures recommended by gas chromatography apparatusmanufacturers.

The IIW mercury method may require 14 to 21 days for complete collection ofall of the diffusible hydrogen in a test specimen at room temperature. The AWSmethod requires 72 hours at 45°C or 6hrs at 150°C for collection of nearly all ofthe diffusible hydrogen escape from the weld metal. Clearly elevatedtemperature speeds up the hydrogen escape from the weld deposit, buthydrogen does escape from solid steel at room temperature

10.3 Effect of diffusible hydrogen content on tensile and ductility of theweld metal.Diffusible hydrogen in the weld metal could reduce tensile and ductility in aslow strain rate test.

Weld metal from a particular batch of E7018 electrodes which typicallyproduces less than 5m1!100g of diffusible hydrogen averaged 27.3 % elongationin the as-welded condition and 28.5% in the "aged" condition.

However, differences in measured tensile, elongation between "as-welded" and"aged" conditions become much more important when electrodes of higherstrength are used.

10.4 Resistance to moisture absorption characteristic of low-hydrogenbasic coated electrodes

As mentioned earlier, basic coated low-hydrogen type electrodes have beendeveloped having moisture-resistant coating. These electrodes have beendeveloped on some of the following measures :

a) Optimised granulametry of the coating flux ingredient

b) A newly developed binder system

c)' Correct procedure used for removing almost entire quantityof moisture from the flux coating

These electrodes after baking have very low level of moisture in the fluxcoating. It is always less than 0.1 % and the typical value is as low as 0.04%.These electrodes when exposed to atmosphere having temp. 27°C +2°C and80% RH absorb moisture very slowly. These electrodes are designated with thesuffix "R" letter according to AWS/SFA 5.12004 specification.

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11. Special packaging for low-hydrogenbasic coated electrodesIt was shown by Franks in 1950 that Low hydrogen type coveringspick-up moisture when openly exposed to humid atmosphere and thatdifferent electrodes absorb different amounts of water under identicalconditions. Smith studied the phenomenon in detail and demonstrated thatdifferent brands of electrodes have different tolerance to moistureabsorption.

While manufacturing low hydrogen basic coated electrodes enough care istaken during baking operation so that almost all quantity of moisture isremoved from the flux coating. Freshly baked electrodes can have as low as0.04% moisture in the coating. Since flux coating of low hydrogen basiccoated electrode is hygroscopic in nature, different manufacturers usedifferent modes of packing.

a) Low hydrogen basic coated electrodes are packed in polythene bagsand then in cardboard cartons. These cardboard cartons are further shrinkpacked.

b) The electrodes are hermetically packed into the metal tinimmediately following production baking. These metaltins may have sufficient quantity of dessicant which canlower the relative humidity in the tin to below 8% ensuringthat the electrode coating does not absorb moisture duringstorage.

c) The electrodes are vacuum packed using special qualities ofpouches and these vacuum packed electrodes are furtherpacked in plastic or cardboard containers.

11.1 The metal tin containers used for vacuum packing are speciallydesigned to provide protection for the electrodes during handlingand storage.

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Table 6 provide' details of moisture level in the flux coating, shelflife of the electrodes for different packing conditions.

TABLE 6

No. Packing condition Moisture in the Shelf lifeFlux coating

1. Cardboard packing with Depends on storage To consultplastic inside and or condition manufactureroutside the carton

2. Hermetically closed tin Usually less than 0.1% 5 yearscontainers

3. Vacuum packed Usually less than 0.1% 5 years.

12.0 Saving in welding costWelding costs which varies from one fabricator to another dependupon the following factors.(a) Drying of electrodes(b) Storage of electrodes(c) Preheating (Power, Labour cost)(d) Reduced labour productivity because working on

preheated work place is more difficult(e) Post weld heat treatment.

Recently developed Low hydrogen basic coated electrodes whichare either hermetically packed or vacuum packed, deposit weldmetal having highly reduced levels of diffusible hydrogen inthe weld metal as well as in the heat affected zone. Such very lowlevel of hydrogen increases tolerance to hardness in the heataffected zone and stresses applied to the weld metal withoutincreasing the risk of cold cracking.

For many applications, where moderate preheat is usually required foreliminating the risk of cold cracking, recently developed vacuum PACKEDBASIC COATED Low-hydrogen electrodes either eliminate preheating totallyor reduce preheating temperature to a greater extent. Reducing preheating or

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eliminating preheating results in savings which is often equal to the cost ofwelding consumables.

Example:

Welding of A516 Gr 70 steel plate of thickness 40 mm. For X meterlength of welding A516 Gr 70 steel thickness 40 mm

us $ 200US$ 250

(a) Cost ofNormalE7018 electrodes(b) Cost of Vacuum packed E7018 electrodes(C) Cost of preheating maintaining inter

Pass temperature (1.5 times cost of electrodes) US $300(d) Cost of storage, backing/drying of

Electrodes( 30% cost of electrodes) US $60

* * Fabricators pay US $ 50 more for vacuum packed electrodes whereas hesaves US $ 360

13.0 Hydrogen controlled consumables &welding consumable manufacturers -capability and experience

13.1 Manufacturers of basic coated electrodes have kept pace with thetechnological development taking place all over the world. Theymanufacture moisture-resistant electrodes of various classifications andthese electrodes are now available in vacuum packed condition.

Even though vacuum packed electrodes cost about 20 to 25% more thannormal cardboard packed electrodes, these electrodes have a much longershelf life and can be used straight on the job after opening the pack. Howevercare should be taken so that the entire quantity of the packet is consumedwithin 4 to 8 hours after opening the pack. Usually vacuum packed lowhydrogen elect odes are supplied in 2.0 kg pouches

13.2 Recently developed basic coated low-hydrogen electrodes have improvedtoughness properties - hence these electrodes have a unique feature calledresistance to ageing of the weld metal for manufacturing these electrodes,electrode manufacturers adopt the following measures:

1) The use oflow carbon clean wire.2) The use of extremely clean minerals, ferroalloys and oxides.

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3) The use of an optimized coating system with a high basicity index.4) Control of Non-Metallic oxide inclusions in the metal which controls the

nucleation process during solidification of the liquid metal and favours theformation of a more fine grained structure.

It is expected that designers and consultants would demand increasingquantities of various, recently developed Low hydrogen basic coatedelectrodes which are either hermetically tin packed for eliminating coldcracking of the weld metal or HAZ of the parent metal.

Conclusion:

1) Hydrogen is an elusive element affecting cold cracking susceptibility in[erritic welds.

2) Hydrogen control assumes criticality as the hardenability increases.

3) There cannot be a compromise on hydrogen control.

4) Procedural differences in measurement of hydrogen does requireperfect understanding and careful comparative interpretations.

5) Low-hydrogen basic coated electrodes, which are available in themarket, deposit weld metal having low, very low or extra low level ofhydrogen in the weld metal.

6) Moisture resistant low-hydrogen basic coated electrodes arenow available in the market.

7) In order to have longer shelf life and cut down cost of welding,fabricators prefer vacuum packed basic coated Low-hydrogenelectrodes.

8) Recently developed low-hydrogen basic coated electrodes deposit weldmetal having improved toughnessproperties and low level ofhydrogen.These electrodes almost eliminate risk of cold cracking.

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References:1) AWS A4.3-86 specification

2) AWS A5.1-91 specification AWS A5.1-2004 specification

3) Evans GM and Christenses N 1971 correlation of weld metal hydrogencontent with HAZ embiitilemeni, Metal construction and British weldingjournal 3:188 to 189.

4) Evans GM and Christeness N 1971, Implant testing effect of steelcomposition and hydrogen level. Metal construction and British weldingjournal 3:263 to 285.

5) Quintana MA 1984, A critiocal evaluation of the glycerine test,Welding journal 63(5) 14 is to 14gs.

6) Coa F R. 1972 The comparison of hydrogen levels IIW Document II-A-305.72.

7) Measurement of hydrogen in [exritic arc weld metal-draft IIW/ISO standard1991 IIW document II-1151-91.

8) Kotecki K.J.and Lafave R.A. 1985, AWSA5 Committee studies of weld metaldiffusible hydrogen welding journal 64(3) 31 to 37.

9) Evans GM 1982, Report 30 August 1982 to WASA5A hydrogen taskgroup members.

10) Japan Welding Engineering Society 1974, Relation between hydrogen contentsby IIW method and JIS methods, IIW Document 11-698-74

11) Japan Welding Engineering Society 1956, Method of measurement forhydrogen evolved from steel welds, IIW Document II-l 073-86.

12) HIRA Y, Minakawa S. and Tsuboi l., 1980 prediction of diffusible hydrogencontent in deposited weld metal with basic type covered electrodesIIW document II 929-80.

13) Maraniellow, E. and Timerman, R. 1990 Influence of the type of ageing on theall weld tension test results, IIW Document II-A 803-90.

14) [. F Mereer "Trends in steel and consumables for welding",Welding Institute Conference, London, 1978 paper 5.

15) Welding steel, without hydrogen cracking, The Welding Institute,Abington, 1973 edition.

16) Coe F R. 1986 Hydrogen measurements, current trends versus forgotten facts,Metal construction 18(1),20 to 25.

17) Achieving high quality welds P L. Threadgill, [an 94.

18) Ruge j. and Dickehut G. 1988, Method for predicting the content of diffusible,hydrogen in the weld metal under the influence of atmospheric moisture.

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