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★-1) Storage and treatment of welding materials 

The following method is applied to the welding of steel structures.

　 1) Coated electrode

　 2) CO₂-gas arc welding

　 3) Non-gas arc welding

　 4) Submerged arc welding

　 5) Stud welding

　 6) Electro slag welding

Ways, (1)∼(5), are mostly utilized on general building, engineering works and bridges and electro-slag welding is used on special structure. Even if we use any kind of method, materials for welding should be proper to quality of base metal, joint geometry, bevel shape and welding method. Also, a care is required in storage and treatment of welding materials.

(1) Coated electrode

It is better to take custody of coated electrode in dried place because moisture absorption is progressed by constituent of covering, grain size, thickness, passage of time, temperature and comparative humidity. To use a moist welding rod makes defects blow hole, in a welding part be occurred. Thus the welding rod that has a possibility to absorb moisture should be used with redrying.

However, we do not redry more than need because covering constituent may be changed in quality. But classifying every type of electrode, diameter in a drier, ilmenite type electrode and low hydrogen type electrode need advisably two of drier caused by difference of dried temperature. 

Dry time is that ilmenite type electrode is 6∼8 hours, and low hydrogen type electrode is 3∼4 hours. Therefore, it is better to use a portable drier with heat-source equipment for using the redried electrode.

(2) Gas shielded arc welding

On solid wire and flux cored wire of CO₂-gas electrode, surface treatment is done with considering rust-prevention, resistance welding time, applying and if it is let alone for a long time it may absorb moisture or rust-occurrence although it doesn't easily absorb moisture compared with covering electrode. Thus the place for storage should be dry and we should use an opening electrode as soon as possible. Also we should pack again the rest. 

★-2) Check point of electrode custody

1) Condition of electrode in warehouse according to kind and rod.

2) Condition of ventilation and dryness in place for storage.

3) Packing condition of wire.

4) Dry condition of electrode before using.

5) Proper fixing temperature in drier according to the kind of rod.

6) Leaving time of a redried rod.

7) Existence of redryness of opened rod.

8) Existence of using portable drier with heat-source equipment.

※ Inspection and revision of welding machine

Welding machine & Cable : In shielded metal arc welding, mostly AC arc welder is used but DC arc welder can be utilized according to the kind of welding rod. In case of the manual welding, inspection of a welder is necessary, because a proper current and voltage are different in line with used welding rod. And in relationship of current and cable length, due to the voltage drop is occurred in case of direct current, enough check about current and rod and length of cable is required.

If the length of cable is too long, to maintain a quiet arc is difficult and especially, AC, required because to control current and voltage can be necessary during welding if too many welding machines are used at the same time in a factory.

In CO₂-arc welding, generally the method including DC constant potential characteristic source of electric power and wire device of applying is utilized.

★-3) Check point of welding machine inspection

1) A length and rod of welding cable.

2) Existence of crack damages of a cable in security.

3) Existence that current and voltage of welding machine correspond with welding condition.

4) A right using way of earth clamp.

5) Condition of repair works about electrode welder and torch.

6) Existence of using device of electric protecting certainly.

7) Check of current and voltage by welding manager during welding.

(1) Welding Gig

A standard position of welding is flat position welding. Therefore, many kinds of welding gig are used for reasonable work, quiet quality and elevation of working ability. A positioner is used in very large works. It make a pillar turn freely with a roller in lower part by attaching the whole of pillar to gig in tack welding. And by doing that, it makes us weld with considering the welding sequence to protect welding distortion at most.

(2) Tools for welding

1) The resistance with base metal is important for a good welding. The case that we earth to welding stand weld on the stand is general, but for perfect welding, we earth to base metal directly and do a sight resistance.

2) Electrode holder : KS or a standardized good is utilized as an electrode holder for safe and perfect welding works, however, to check often, especially to remove spatter in nozzle of semiautomatic welding torch, is important and if we neglect removing works, flow of gas is getting worse and this have an effect on welding bead seriously.

★-4) Check point of welding gig

1) Using Gig is suitable or not for welding works.

2) Stability is good or not in works.

3) Welding process and the way to use gig is right or not.

4) Existence or not of the study about Gig can give a hand for quality control and elevation of efficiency.

(1) Welding works

For a good welding, included working accuracy and pit up accuracy, enough check of welding condition and welding sequence and qualification and many experiences of welder are required. There are many reasons that welding defects are occurred. But main reasons before everything are lack of included working accuracy and bad concentration. 

Anything of narrow root opening, small included angle, large root face and bad back plate adherence comes under one of these. And we can know that many welding defects are occurred with many experiences. 

Thought to weld completely is very difficult, we should reduce defects at most, perfect melted welding zone is the same with main stress under structure.

ⓐ Weld face cleaning :

Things that hinder in welding, dust in beveling, water, oil, rust and so on, should be removed. Especially if water remains in gab of base metal or back plate, that becomes a cause of blow hole or weld crack, thus to dry enough is important. Also, if we don't remove weld slag between each of stories carefully, that becomes a cause of slag inclusion, thus special care is required.

ⓑ Control of welding voltage and current :

The proper current is changed by welding position, welding rod and welding process. And also by using condition of electric power in a factory voltage drop is occurred. Therefore, sufficient care is necessary to control welding current and voltage decided by welding condition and to maintain the value measured near welding holder by portable ammeter is advisable. In semiautomatic welding, because welding current, voltage and gas discharge are changed by a kind of material, thickness and welding position, scrupulous care is necessary. Due to strength and weakness of current affect on undercut or overlap directly, administration is important

ⓒ Atmospheric and temperature :

Welding has something to do with atmospheric and temperature and when temperature is low and wide rain are strong care is necessary in welding works. In case that temperature is 0℃ or less, it is better to preheat. And in high humidity or strong wind, to consider cautions about welding like dryness of welding face and protection against wind is important.

★-5) Check point of welding work

1) Selection of welding materials is suitable or not.

2) Check of welding machine and cable are good or not.

3) Check or not beveling working degree of base metal.

4) Clean condition of the weld's face is good or not.

5) Control of welding current and voltage is comfortable or not.

6) Welding position and working environment are good or not.

7) Welding gig is proper or not.

8) Examine or not wind break, damp proof countermeasure and existence of preheating.

9) Treatment of welding materials is comfortable or not.

10) How is security counterplot including electric protecting

(1) There are shape dimension defects and construction defects (inside defects) in welding defects.

In case of shape dimension defects, we can judge the degree with visual and measure but in case of structural defects, we can confirm existence of defects only by radial rays test or ultrasonic test.

A kind and degree of defect can be harmful to structure internal force of structures. Therefore to inspect seriously and in defects, after counseling with the person connected with the construction and confirming the cause, kind and location, to decide existence of repair is advisable.

(2) Shape dimension defects

ⓐ Dimension lack and excessive : There are lack of leg length, throat dept lack building-up lack and building-up excessive in lack of dimension. And we do welding repair to defects like these. Because bad shape gives notch effect to the welding part, it should be regulated by disk sand. As a welding rod used for repairing bead shape, the rod has 4mm or less diameter is good.

ⓑ Undercut

Due to undercut by welding make the effective sectional area reduce, it is a serious default in structure internal force. if the length of undercut is longer than 1mm, it is repaired certainly, we should be careful not to be short bead and use small rod is advisable. undercut is occurred when current is too strong and the repair welding by semiautomatic welding can remove defect with doing in weld heat input lower than reasonable value.

Because the undercut occurred in edge of welding gives notch effect to column flange material, it is a serious problem in base metal strength. Thus we should construct carefully.

ⓒ Unbalance of bead

Overstatement or scantiness in bead, leg length of welding bead is unbalance, bead gab is unbalance, and so on, is the one of shape defects. The bead that leg length is deficient is needed reinforce because it has a problem in internal force.

ⓓ Crater

Crater is that melting pool is sunken and it is occurred by cutting arc quickly on terminus zone of welding bead. Though the crack occurred by deflation of crater zone is small, it progress continuously. Therefore it is important to make crater zone flat by build-up welding. we should be watchful against arc because crater is also produced when we connect welding rods.

ⓔ Round welding

In welding of material terminus zone, it is rule to do round welding on sequent bead if the part has not end tab. when we weld both of side, we can see that final edge is finished by short bead. However, it should be avoided when tension effect because it becomes structural defect. So a good welder does round welding.

(3) Structural defects

ⓐ Blow hole & pit

Welding defects called blow hole and pit are produced if occurred gas doesn't escape when deposited metal is solidified. Blow hole is occurred when gas remains in welding metal and the hole at gas escapes on bead face is pit. It is better to inspect sufficiently and repair air gouging blow hole, because rounding defects may remain in deposited metal.

Main causes of these defects are

-badness of welding rod and absorption of water

-case that a welding part include moisture

-unsuitable are length, current and treatment

-adherence of oil, paint, rust and so on to a welding part .

Due to these defects have round shape, it is difficult to be found out by ultrasonic test. Thus we should be careful about treatment of welding rod and dryness of a welding part.

ⓑ Slag inclusion

Covering of welding rod melts and come up to the surface of deposited metal. and then it becomes slag, but defects caused by slag inclusion are that some parts of slag leave inside of deposited metal. The defect is easily occurred when welding current is low, manipulation is not appropriate and slag removal every layer in multi-layer welding is not enough. Defects caused by slag inclusion are easily found out by ultrasonic test and radiation but care about slag cleaning current and manipulation is required because they are in deposited metal and repair is so difficult.

ⓒ Incomplete penetration

Incomplete penetration is that a middle part of board have been left with not being melted when thick board is done butt welding with no repair works. Also, incomplete penetration may be occurred partially due to arc concentration of welding rod. incomplete penetration is easily occurred on root face if the size of root face in betterment is large, and bevel angle is small. to prevent incomplete penetration, we should make beveling working accuracy better. In addition to that, if there are defects when welder inspects, he should repair. Moreover the location where defects are easily produced changes according to welding place and welder.

According to location where incomplete penetration is occurred, we should do gouging and reweld most of deposited metal. Thus welding heat input to base metal gets to be large and cause quality change of heat-defected zone. These defect can be prevented by careful welding work.

ⓓ Bead crack

Weld metal can be divided into hot cracking and cold cracking. Hot cracking is that low ductile welding metal is cracked by tension of contraction stress in grain boundary. Cold cracking is occur red by getting cold on 300℃ or less in welding metal and is easy to occur into root crack with one pass of welding.

Crack is the most serious before any defect occurred welding part so it is the defect must not be occurred. Where this defect is easily occurred are the tack welding part, crater zone part and immense restrict welding part. Crack is often produced as cold cracking. affection of hydrogen by absorption of welding rod, large carbon equivalent of base metal, immense restrict of welding part, sudden heating and radical cooling are thought as its reasons. Therefore counterplot, like preheating, is necessary according to dryness of a welding part and rod, using low hydrogen type welding rod. In case of Co₂-semiautomatic welding, due to micro cracks are easily occurred on welding metal, bevel geometry that thickness of 1 pass is not thicker than bead wide is required. Beside, we should be careful especially because this defect cannot be found out on surface.

(4) Weld defects and counterplot

As the purpose for using, welding is divided into things that are required the water tight, and the air tight, are accounted much of the visual of weld face, are needed the equal or more strength with the ba se metal on weld zone, or require the only extent can be attached. Welding is joint with sudden heating and melting of cooled materials. careless welding can not avoid occurrence of defects. So we show causes and counterplot of occurred defects on chart.

· Defects and counterplot of coated welding part