Hydrogen Induced Craking

8/10/2019 Hydrogen Induced Craking

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Hydrogen induced craking ( cold cracking)

Hydrogen induced cracking also referred to as cold cracking, is caused by the diffusion of hydrogen in thecrystal lattice of HAZ near the fusion boundary. Atomic hydrogen is dispersed throughout the materialmaking it weak in mechanical properties. The entrapped hydrogen makes cavities in metal that results in

cracking due to weak ductility and tensile strength. When metal is subjected to tensile strength and highhydrogen concentration, hydrogen induced cracking occurs. Hydrogen cracking is also named as toecracking or under bead cracking due to its location of occurrence. It primarily occurs in High strength Lowalloy steels. During welding hydrogen is induced due to the moisture and organic compounds by the usageof cold cellulosic electrodes. Proper cleaning of metal surface and pre-heating are the preventive steps toavoid alarming hydrogen induced cracking. Below listed are the ways to reduce Hydrogen cracking inwelded items.

1. Pre-HeatPre-heating is one of the best step to achieve good solidification microstructure as it slows down thecooling rate. In this way controlled cooling provides the desired microstructure not prone to hydrogencracking. In worst the rapid cooling results in sensitive microstructure to HIC.

2. Interpass Temperature Define the peculiar interpass temperature. Once this temperature is specified, the base metal must be pre-heated to that temperature before depositing the other weld pass. In this way cooling rate is controlled and

the mechanical properties of both weld metal and HAZ are secured, avoiding hydrogen cracking.

3. Post-Heat After welding is finished, apply post heat to eliminate any remaining hydrogen. On heating the metal givesoff the hydrogen that lessen the risk of hydrogen induced cracking after welding. Moreover post weld heattreatment (PWHT) is also applied for the removal of harmful residual stresses and desired micro-structureis achieved.

4. Suitable arc process Metals that are prone to hydrogen cracking must not be welded by the arc processes that induce hydrogenin the weld metal. MIG welding with surface tension technology is the recommended process for weldinghigh strength low alloy steels, rather than applying stick welding with cellulosic electrodes. In latter casehigh diffusion of hydrogen occurs that leads serious cracking in steels.

5. Suitable filler metal As mentioned above cellulosic stick electrodes are the mean of hydrogen embrittlement. Moisture and theorganic compounds are the source of hydrogen. Such electrodes provide hydrogen gas shielding. On theother hand basic electrodes (minerals like calcium and magnesium carbonates) give low hydrogenshielding, reducing the risk of cracking in low alloy steels.

6. Multipass technique Multipass method renders tempering effect, modulating the microstructure in order to get rid of hydrogencontent. Each pass tempered the previous deposit pass and protect it from cracking. On the other hand hotpass is also applied for same purpose. We know hot pass is used to clean the root pass by the removal ofslag content. Moreover it is also applied to render heat treatment effect so that root may not be subjected tohydrogen cracking.

7. Temper bead technique Temper bead technique is introduced to provide the heat treatment effect in repair welds where post weldheat treatment is difficult. In this technique overlapping of beads assist the self-heat treatment that refines
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the course grain zones, providing desired microstructure with improved properties in both weld metal andHAZ. Furthermore it also minimizes residual tensile stresses. All these features encourage the reduction ofhydrogen induced cracking.

8. Shielding gases As it is stated above cellulosic electrodes offer hydrogen gas shielding. Moist free (low hydrogen) shieldinggas must be used in case of metals that are prone to hydrogen cracking. Use of backed electrodes is therecommended practice in order to lower the hydrogen content.

9. Rust and scale removal Before welding, cleaning of joint with removal of rust and scale, is always endorsed. Since the presence ofmoisture or grease on parent metal, is the major source of hydrogen. So the joint must be rust free andproper cleaning is the paramount activity before the commencement of weld.

10. Fusion Perfect fusion is achieved by the merging the weld metal that provide reinforcement to the weld toes. Asstress concentration is one of the cause for hydrogen cracking/toe cracking. Reinforcement at weld toesreduces stress concentration and thus avoiding the toe cracking.

Comments

In brief residual stresses, high hydrogen content and sensitive micro structure are the primary causes forhydrogen cracking. Control of these elements gives a cracking free weld. In order to achieve control propercleaning, pre-heating, nickel and austenitic fillers and multi-pass method are recommended practices.- See more at: http://www.weldpedia.com/2014/08/10-ways-how-to-control-hydrogen-induced.html#sthash.rAYxrvom.dpuf

Fracture tests for welder qualification Inspection , Qualification Tests 3 comments

Fracture tests are conducted to qualify a welder by the examination of fracture surfaces of a weld metal

rather than using expensive macroscopic examination. The procedure is applied in order to assess thequality of test weld made by a welder. Although standards elucidate the test procedure, test location,

technique, dimensions and type of specimen. There are two types of fracture tests; Fillet weld fracture and

Butt weld fracture in which a notch is machined on the weld metal that enables the specimen to fracture

easily. Following are the critical points regarding these tests.

Nature and dimensions of Test specimens Number of tests Location of test What is the method and technique for making fracture

Weld defects that ought to be detected Job description of an inspector
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Butt Weld Fracture

The procedure is applied to observe the fracture piece of groove weld in order to detect the weld

imperfections. Common problems like solid inclusion (slag, flux, and oxide), porosity and lack of fusion

have severe effects on groove weld, can be detected by simply breaking the test weld. No other technique

like radiography is used that may be expensive.

Test specimens taken from the groove weld are notched in order to take fracture path from the middle of

the weld. That is why it is also known by a term Nick Break Test in industries. The techniques that are

used to cause fracture are; three point bending and hammering. You can split the weld parts by simply

hammering or on the other if the test piece is supported on two points and the load is applied from the

above, required breakage is obtained.

Fillet Weld Fracture

With the same procedure and objective as butt weld fracture, fillet weld fractures are used to qualify a

welder for fillet weld tests. Fracture is made to find out the weld imperfections that may harm fillet weld.

Defects like porosity, lack of penetration, solid inclusion are observed on fracture surface of split parts.

Dimensions and nature of test piece are specified by the standards and codes and required specimen is

obtained accordingly. A notch of specific profile is indented on the weld. Normally the shapes of notch are;

V-shaped Square profile U-shaped

Specimen are placed in specific direction or clamped is special tools to achieve the required fracture

through throat. After placement, hammering or pressing is applied and the split parts are ready for

examination.
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What is the job of Inspector?

Inspector must have a close examination throughout the procedure. After observing the splitting/ breakage,

he must identify the weld defects with great care. It is essential that he has work experience about

determining the imperfections on the fracture surface and assisting others to conduct the procedure in right

way. Moreover he should give a systematic report containing meaningful information about;

The shape of fracture Imperfections and types Position of imperfections on Butt/Fillet weld surface

Last comments

Fracture tests are conducted a s a second choice for welders qualification in place of other examination

techniques as it serves for the same purpose of visualizing the weld defects deep inside or at the root of

the weld.

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Mechanics of Crack Tip Opening Displacement Defects , Equipments , Inspection , Qualification Tests No comments

Crack tip opening displacement is kind of a destructive testing that is applied to measure the fracturetoughness of the material. In shortened form the method is known as CTOD. In this technique a notch is

made on the test material and subjected to bending at specific temperature (usually at low temperature)

until the crack initiates. Bending is applied in such a way that the crack tip opens widely and the extent of

opening without brittle fracture is measured as toughness. The technique proves quite useful in repair work

when the crack is appeared during service. Following is the demonstration on mechanics of crack tip

opening displacement.

Specimen
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Before repair weld After repair weld After final treatments

Certain techniques are used to determine the intensities and magnitudes of defects and assist to find out

their possible causes. Therefore suitable repair technique is specified accordingly. After applying repair

weld non-destructive examination is also required to make sure that the defects have been completely

eliminated. Specific NDT technique is selected and acceptance criteria is defined according to the job

requirements. Moreover some terminal techniques are also required after post-treatments to check the

complete removal of defects.

Competent welder

Welder must be qualified for the repair job and should have previous work experience. As it is stated earlier

that repair work mostly involves hand operated procedure. A welder must be cautious during depositing the

weld and prevent serious problems of distortion and unwanted stresses. Management staff only allow the

authorized welder for the repair work.

Cleaning of repair portion

Before repair it is recommended to ensure the removal of coating, paint, and oil/grease from the section

where the weld repair is to apply. Various pre-cleaning techniques are used for this purpose so that therequired surface is prepared and defects free results are achieved.

Inspection Staff

People in inspection circle have an essential role in evaluation and estimation of weld quality throughout

the procedure. During production an Inspector or NDT personnel ensures the quality of weld according to

the quality plan. If the defect is detected during visual inspection then analysis and assessment lead the

inspector to approve repair weld and after that inspection and non-destructive examination may also

require after excavation process, repair weld and even after final treatment like post weld heat treatment.

In case of service repair weld, failure analysis is carried out to find the reasons for deviating the

performance of an item.

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Why is an Impact Toughness Test required inWelding Equipments , Inspection , Qualification Tests No comments

Charpy V-notch test is used to determine the toughness of the weld output by measuring the energy tofracture a notched test sample. As toughness of steel for specific application must be adequate enough to

prevent any brittle fracture loss but low alloy steels may lose their toughness at quiet lower temperature. So

after welding the specimen is tested at the specific temperature to determine the relative impact toughness

and consequently evaluate the weld materials. The test is applied to assess the quality of weld output. It

dont give the fracture toughness that is entailed in service estimations.

What is toughness?

Toughness can be defined in two ways.

Resistance to brittle failure in a material. A tougher material will show more resistance to brittle fractureand cracks.

Energy required to cause a brittle failure. So more energy will be required to get brittle fracture in atougher material.

Why impact toughness test?

In carbon and low alloy steels, change in fracture toughness is associated with the change in temperature.

With the decrease in temperature, these materials turn to brittle from ductile nature. Plot of impact energies

against the temperature gives S curve, which is divided into two shelves; upper shelf and lower shelf.

Above mentioned steel types show ductile behavior at the upper shelf and switch to brittle nature when the

temperature falls to the lower shelf. The temperature at which the transition of ductile to brittle occurs, is

called transition temperature.
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From the above discussion it is important to have a sound knowledge of temperature at which the

change in fracture behavior may occur and for weld structure to perform at the upper shelf temperature.

Specimens

Codes and standards demonstrate the dimensions required for impact test specimens. Normally they are

10mm x 5-7.5mm x 55mm. Energy values may tend to vary for the same test so three specimens are taken

for each test and an average is calculated from the energy values. The location of specimens within the

weld and even the position of notch on the specimen is quiet an important factor in evaluating the impact

energies.

Test Machine

Impact testing apparatus has an I shape appearance and consists of anvil at th e lower portion and scale

assembly (graduated scale with a moving pointer) at the upper end. A pendulum hammer swings from a

specific height and strikes the specimen placed on the anvil.

Standards

Standards for Charpy V impact testing are BS EN ISO 148-1 and ASTM E23.

Procedure

First the specimen with notch is allowed to cool at the specific temperature by immersing in liquid/gas

container. After the temperature is stabilized, the specimen is quickly shifted to machine and the hammer is

impacted behind the notch. The height through which a hammer swings, is the measure of energy. The

energy in joules, utilized to break the specimen is recorded on the machine scale by the movement of a

pointer on that scale.
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After taking average, a comparison is made between the test results and the values specified in

codes and standards. The comparison tell us whether the specific requirements have been met or not. On

the other hand this test also tell us about some toughness attributes which are;

Crystallinity If fractured surface has crystalline appearance, the fracture will be brittle. More the

crystallinity more the brittle fracture and vice versa.

Expansion If the fracture halves from behind the notch are expanded, specimen will have moretoughness. It is better to say that more the expansion more will be the ductile fracture. On the other

hand less the lateral expansion more will be the brittle fracture.

Last Comments

For impact testing, correct adjustment of welding parameters is important, as values may be changed dueto welding consumables, heat input, post treatments, composition and many other factors.

Aluminum alloys and austenitic stainless steel (300 series) are used in cryogenic applications because they

dont exhibit fracture beha vior change as the temperature falls.

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What makes STT exceptional in open pipe root pass Equipments No comments

Surface Tension Transfer is referred to as STT technology. STT is the advanced mode of Metal Inert Gas

with controlled waveform that runs outstanding root pass with less time in open pipes. STT offers

innumerable advantages over traditional arc processes. Different modes and arc processes can be

activated on a single equipment. Here is the explanation of some benefits that make STT technology

unequalled in root pass and fill ups. See the usefulness of Surface Tension Transfer.

Ease of learning
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Very of easy and simple to learn and welders can learn its usage quickly. Less training time eliminated the

complexities that were faced in learning traditional TIG, Stick, MIG, and FCAW.

High quality weld

STT provides outstanding and exquisite weld in jobs that require one hundred percent inspection. Easily

accessible for fill ups and gaps up to 5mm (3/16 inch). Prominent weld profile and definition with minimum

defects is achieved.

High output

Its usual practice to apply TIG welding for open pipes root pass to achieve defects free, uniform and

consistent weld. But TIG is a slower process and does not provide high yields. STT offers more productionwith almost four times faster travel speed as compared to TIG process.

Thicker weld

It deposits thicker welds as compared to other arc systems. Root and hot passes with Stick welding dont

meet the required thickness. As a result thinner welds are subjected to weld defects, incomplete fusion and

not proper sized welds. On the other hand weld passes with STT technique are almost two times thicker

than the Stick welds.

Low hydrogen weld

It produces crack resisting low hydrogen welds that are highly suitable for high strength steels. Root pass

with Stick cellulosic electrodes, have highly diffusible hydrogen that leads to cracking in high strength

steels. Surface tension transfer technique runs one thicker pass almost equivalent to two passes of Stick

welding. This eliminates many defects and good fusion, excellent bead shape and size is obtained. It

provides the means of lower pre-heat temperature welding and thus alleviating problem of cracking in high

strength steels.

Controlled arc and amperage

With waveform control arc energy is precisely regulated and adjusted during each cycle. This technique is

easy to use as controlled waveform does all the work. In this technique the current is reduced at certain

interval to minimize the spatter and fumes while at certain intervals, current value is increased to give

quality weld with excellent fusion. Unlike MIG welding, short arc is kept stable, eliminating fumes and

spatter.

Back bead control


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During root pass STT runs a consistent weld control back bead at the inner side of the pipe. High peak

current is accessible to the inside through joint gap, ensures good fusion to the gap sides.

Easy to use

Operating the equipment is as easy as pressing the button and your job is done. Welders can change

easily configure and change the modes by simply turning the knobs.

Sensor

For the monitoring and changing of arc voltage, sensor is used in STT technology. Normally a sensing lead

is used for this purpose which is connected near to the joint with the help of magnetic source. This sensing

device controls the arc voltage and waveform and consequently continuous feeding with no spatter andfumes.

Modes switchable

This one is the unique feature in STT technology equipment. After the root pass with STT mode, welders

can switch to the MIG mode, to run next passes. Aside from root passes the equipment is also applied for

high quality fill up passes with minimum downtime. Activation of MIG mode by simply pressing the gun

trigger. Moreover if you want to apply gas-shielded Flux cored arc welding, switch to the other gun which is

readily installed on the same equipment. For large diameter pipe welding, submerged arc welding process

can also be activated on the same equipment.

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Macroscopic and Microscopic Examination of WeldHardness Equipments , Inspection , Qualification Tests No comments

Resistance to plastic deformation is referred to as hardness of the material. A specific type of indenter is

used to indent the material and the determined resistance to indentation is the measure of hardness of that

material. Hardness value is associated with the indentation size which may be actual surface area or the

depth of indentation. Hardness value of a material depends on other metallurgical properties viz; tensile

strength, elasticity, plasticity, toughness, stiffness etc. Modern Hardness testers are shown below.
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How is Hardness determined?

Hardness can be measured in three ways. There are three methods for the calculation of hardness.

Indentation By determining the resistance to plastic deformation. Scratch - Resistance of material to fracture/deformation when subjected to scratching or abrasion. Rebound Determination of length to which diamond tip hammer bounce, if it is allowed to drop on a

material from a specific height.

Why Hardness test in Welding?

In welding, Indentation method is used to measure the hardness value. Weldment with hardness above the

specific limit may susceptible to serious cracking. According to quality control plan, weld specimens are

tested so that there is no region in weld that has hardness above the specific limit. The specific areas

where the hardness is measured are;

Base Metal Weld Metal Heat Affected Zone

Weld Harndess Examination is classified into two categories; Macroscopic and Microscopic. Former is

used during fabrication where the specimens of bigger components are prepared. Later is used to

investigate the hardness of smaller sections or the micro components of metal with the help of microscope

and many other modern techniques.

Macroscopic Indentation method includes

1. Brinell Hardness Test
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A steel ball of specific diameter is used to indent the material with specific range of loading force for a

predetermined time (normally thirty seconds). Range of steel ball diameter used is 2.5-10mm and that of

loading force 1-3000kgf. A particular diameter/load ratio is used for particular type of material in order to get

accurate results for example 30:1 ratio is selected for steel alloys. In this method hardness value is

calculated by dividing the load force by surface area of impression.

For harder materials tungsten carbide ball is also used in place of steel ball and hardness up to

600 BHN can be measured. One disadvantage of Brinell Hardness Test is, too large the indentation due to

large ball diameter. This test cant be applied for hardness analysis of various HAZ regi ons where harndess

may vary from region to region. For this, the test is frequently applied for hardness evaluation of base

metals.

2. Vickers Hardness Test

With the same principle to Brinell Hardness Test, Vickers uses a square based diamond pyramid indenter

to make impression on the material. The 136 degree diamond indenter withstand high load without any

deformation. Also the indentation depth does not have any influence on hardness, hence load/diameter

ratio is not so important in Vickers Hardness test.

Unlike Brinell, it gives smaller indentations and may be applied for hardness survey on smaller sections of

heat affected zone, weld runs. The test surface must be flat with the indenter upright to obtain accurateresults and Vickers Hardness Test satisfies this requirement.
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3. Rockwell Hardness Test

It is performed by loading the particular shape and size of indenter on the material to make an impression.

Indenter may be a steel ball or 120 degrees diamond cone and the applying load can be 60kgf, 100kgf or150kgf.

Procedure

In the start of the test, lower load is applied to make an impression and after that the required load is

applied on the material to make an indentation. Different scales ranging from A, B, C K are specified for

the hardness analysis of different materials. For example Scale B is characterized by employing steel ball

indenter and used to measure the hardness of softer materials while Sale C is characterized by diamond

cone and applied on harder materials.

Moreover Rockwell Hardness Test can also be used to test the hardness of thin materials likecoatings, sheets/strips and ceramics.

Microscopic Examination includes

4. Knoop Test

Like Vickers Hardness, it also uses a pyramid shaped indenter to make an impression on material but with

minor load (ranging from few gram force to 1 kilogram force). Impression is too small that need some

microscopy aid for visual analysis.

5. Ultrasonic Test

This test is not associated with indentation principle hence not listed in dest ructive testing. Here Frequency

Resonance Principle is used in this kind of test where a vibrating metallic rod is brought in contact with the

test material. Due to which a change in frequency resonance occurs which is actually a measure of

Hardness.

Moreover potable equipment are also available to test the hardness of bigger weld components or the weld

structure in service. One common test is Leeb Rebound Hardness Test.

6. Leeb Rebound Hardness Test

Type of a portable hardness where a hammer is rebounded after striking the material and the length of

rebound is measured as the hardness value. The equipment must be calibrated correctly and personal

must be well trained, in order to get accurate results.


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Hardness Value Interpretation

As it is described earlier, different scales are assigned to different material hardness. Following is

demonstration of hardness values with alphabetic letters.

Examples

32 HRC in which hardness is 32 units by Rockwell Hardness with diamond cone using the scale C. 438 HV30 in which the hardness value is 438 by Vickers Hardness Test using 30Kgf load. 340 HBW in which the hardness value is 340 by Brinell Hardness Test using Tungsten Carbide Ball. 55 HB10/500 in which the hardness value is 55 by Brinell Hardness Test using 10mm steel ball by

applying 500kg load.

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7 Effective Ways to Prevent Lack of FusionDefects , Inspection , Multi pass , Tactics 2 comments

Failure to complete amalgamation with parent metal or between the weld runs, is referred to as lack of

fusion in welding. The weld metal fails to blend with parent metal or sometimes two weld beads are not

completely fused to make as a whole. The problem occurs when the work piece not receive adequate heat

for fusion. The unfused part sites at three places;

Along the joint wall

Between the weld runs

At the root

Following are the possible causes of lack of fusion and the practicable ways to control them.
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1. High Heat Input

As it is stated earlier that less heat supply results in poor fusion. We know heat input is the relation of

welding voltage, current and travel speed. It has direct relation with current and voltage and that of inverse

with travel speed. Low voltage/current settings dont supply enough heat. On the other hand too faster

travel induces the same problem. Adjust the maximum allowable current and blend weld metal with

moderate pace. Here great skills are expected from a welder.

2. Scale/oxide removal

Weld joints can be subjected to atmospheric contamination. Any unwanted particle or presence of oxide

film may impede the process of fusion and may harm weld properties. Therefore it is recommended to

remove any overlay on the joint. Joint cleaning prior to welding makes it easier to eliminate lack of fusion.

3. Correct Angles

Electrode and work angles play an important role in achieving best quality results. Make sure the right

electrode angle with moderate pace. Incorrect electrode handling makes liquid weld to interrupt arc activity.

4. Bead Orientation
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Wrong positioning of weld beads along the joint wall creates slot and fissure between them. This slot is the

critical point of slag inclusion. A welder must be trained enough, to put the beads in right place and ensure

the complete blend of weld beads along the side wall.

5. Position welding

Root pass with vertical down position creates disruption in the process and may result in partial fusion. In

order to prevent this, vertical up position is preferred.

6. Edge Preparation

Well prepared edge is an essential part of perfect welding. If the joint pieces are not aligned in the same

plane, variation occurs in root attributes. Furthermore if the root face is too large, weld metal fails to fusecompletely at root. Fix the problem by preparing small root face edge. On the other hand, small root

opening also results in unfused outcome by influencing the aspects of fusion and it is recommended to

confirm the correct root opening before commencing the welding procedure.

7. Correct voltage and Inductance

During short circuiting mode in MIG/MAG process, inductance level may exceed up to the certain level

which can cause severe fusion problems. It is only the matter of fact that the magnetic field produced due

to immoderate inductance, resists the welding current to rise. In this case metal at the wire tip is not heated

adequately and fails to fuse with parent metal. Appropriate adjustment of voltage and inductance settings

are required to prevent spattering and lack of fusion, as too low inductance also causes severe spattering.

Use of modern equipment with advance power source (that provides regulated voltage and inductance

values) is appreciable.

You May be Interested In:Defects Inspection Multi pass Tactics

9 primary reasons for using CO2 shielding in GMAW of Carbon Steels

7 Effective Ways to Prevent Lack of Fusion

What causes Weld Tungsten Inclusion

How to MIG weld Square Tube

7 Effective Ways to Prevent Lack of Fusion

Mechanics of Crack Tip Opening Displacement
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0 Comments

2 Comments

Facebook Comments by Blogger Widgets

2 COMMENTS:

1.

Gerald Austin 7 October 2014 09:06

You may have touched on it in your text but it wasn't clear. Here are some things that can also cause lack

of fusion.

Excess Voltage with GMAW/FCAW. As you increase the voltage and change no other parameters, thedepth of penetration decreases.

Too SLOW of a travel speed. Often time the "textbook" cause related to speed is excess travel speed.

However as speed slows down, the molten weld metal thickens, as it thickens, the arc is not as close to the

base metal. Thus increasing the likelihood for fusion/penetration type discontinuities. The slower travel

speeds keep the arc from staying on the leading edge of the puddle. Travel angle can also contribute to

this for the same reasons.

POSITION. I have seen more defects while working on piping jobs at or near the top of a pipe than EVERon the sides (Horizontal Pipe Centerline). Best position to have complete penetration and fusion ?

VERTICAL uphill. But may not be the most productive. The arc is ALWAYS on the front edge of the puddle

then.

Reply

Replies

1.

Mekaal 10 October 2014 06:40

Agree with you Austin. Specially the vertical uphill position is best to avoid various defects. Moreover

electrode and work angle has an important role to get best fusion results.

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10 causes of weld porosity and their practicable

preventions Defects , Inspection , Tactics No comments
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20/22

Porosity is referred to as cavity produced in weld due to the entrapment of gas. This introduction of gas in a

weld is supported by some mistakes that ought to be eliminated. In weld metal porosity is categorized

according to shape and location of occurrence. Some gas cavities occurs in spherical shape, some in

elongated (like in case of worm holes) while on the other hand some cavities occur throughout weld metal

and some on the weld surface. These gas cavities appear either singly called voids or uniformly distributed

throughout the weld and sometime developed in clustered form. These voids and cavities are produced

primarily by gas entrapment during the solidification procedure of weld. So making prediction about

mistakes that causes porosity and their removal is essential before welding. Given below is the complete

detail about common porosity reasons and their solution.

1. Moist electrodes

It is recommended to use baked electrodes in Stick welding process in order to avoid moisture content. In

worst heat draw steam during welding which creates small cavities in the weld metal. It eventuates when

stainless steel electrodes or low hydrogen electrodes are not properly kept dry. In low hydrogen electrodes

some moisture is required within a limit for better performance but is some case if moisture exceeds fromthe limit, the weld metal will prone to porosity. For prevention parent metal must be preheated in order to

remove any moisture. Also the electrodes must be stored in dry conditions and must be oven baked before

use.

2. Contaminated surface

Parent metal or electrodes may be subjected to atmospheric contamination. Any grease, oil or moisture

content on surface contribute gas formation when exposed to welding temperature and may cause porosity

problems in weld. In order to fix it, clean the material by specified surface preparation procedures.

3. Improper Gas Shield

The possibility of air entrapment due to inconsistent gas shield may cause porosity problems. For this the

welder must check gas hose attachment with the equipment and remove hose contamination if any.

Correct connection prevent any loss of gas shield and consequently no air entrapment. Moreover air flow

and draughts in shop can cause restriction in gas flow. So proper screening is required to avoid such kinds

of restrictions in gas flow.
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4. Too high gas flow

High flow rate of gas shield setup turbulence and may draw air into the weld metal. Optimize gas flow

provides quality welds with no gas loss. Moreover it saves cost on the other side.

5. Inadequate electrode deoxidant

During solidification, the excess oxygen come out from weld metal due to reduced solubility and may

undergo carbon monoxide formation that may cause porosity. For this some deoxidants are added in

electrodes, filler metals and even in parent metals to remove the oxygen. Therefore inadequate deoxidants

may result in poor deoxidation and are responsible for weld defects. In order to prevent this, use electrodes

with adequate deoxidants.

6. Too high arc length

Too much longer arc length in other words high voltage can also cause weld porosity. If the welding gun is

held away from the joint keeping arc length longer, the magnitude of shielding is reduced which may lead to

air entrapment from atmosphere. Correct arc length is recommended primarily to avoid draughts/breezes.

7. Incorrect surface treatments

Release of gas during painting/surface treatments can impair weld characteristics. Treatments like zinc

coating or galvanizing produce gas and other unwanted particles. In an endeavor to fix this problem, make

predictions about the chemical reactions before specific surface treatments.

8. Open work surface

Any surface which is open to atmospheric air can be contaminated. Air introduction from back side through

root opening, gets entrap in the weld puddle. Make sure that weld joint is protected from such kinds of

crevices.

9. Laminated surface

Laminated surface also creates disturbance in welding. In case of welding laminated work piece, prepare

un-laminated parent metal to conduct quality weld procedure.

10. In-appropriate flux


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Welding flux must be treated with great care as they have capability to absorb moisture (granular SAW

flux). They must be supplied in dry condition. On the other hand, use of low activity flux results in surface

porosity. Use of high activity flux offers quality welds with no porosity.

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