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This term is used to describe the failure of the filler and base metal to fuse together at the root of the joint. Bridging occurs in groove welds when the deposited metal and base metal are not fused at the root of the joint. The frequent cause of incomplete penetration is a joint design which is not suitable for the welding process or the conditions of construction. When the groove is welded from one side only, incomplete penetration is likely to result under the following conditions.

a. The root face dimension is too big even though the root opening is adequate.

b. The root opening is too small.

c. The included angle of a V-groove is too small.

d. The electrode is too large.

e. The rate of travel is too high.

f. The welding current is too low.


Lack of fusion is the failure of a welding process to fuse together layers of weld metal or weld metal and base metal. The weld metal just rolls over the plate surfaces. This is generally referred to as overlap. Lack of fusion is caused by the following conditions:

a. Failure to raise to the melting point the temperature of the base metal or the previously deposited weld metal.

b. Improper fluxing, which fails to dissolve the oxide and other foreign material from the surfaces to which the deposited metal must fuse.

c. Dirty plate surfaces.

d. Improper electrode size or type.

e. Wrong current adjustment.


Undercutting is the burning away of the base metal at the toe of the weld. Undercutting may be caused by the following conditions:

a. Current adjustment that is too high.

b. Arc gap that is too long.

c. Failure to fill up the crater completely with weld metal.


Slag inclusions are elongated or globular pockets of metallic oxides and other solids compounds. They produce porosity in the weld metal. In arc welding, slag inclusions are generally made up of electrode coating materials or fluxes. In multilayer welding operations, failure to remove the slag between the layers causes slag inclusions. Most slag inclusion can be prevented by:

a. Preparing the groove and weld properly before each bead is deposited.

b. Removing all slag.

c. Making sure that the slag rises to the surface of the weld pool.

d. Taking care to avoid leaving any contours which will be difficult to penetrate fully with the arc.


a. Porosity is the presence of pockets which do not contain any solid material. They differ from slag inclusions in that the pockets contain gas rather than a solid. The gases forming the voids are derived form:

(1) Gas released by cooling weld because of its reduced solubility temperature drops.

(2) Gases formed by the chemical reactions in the weld.

b. Porosity is best prevented by avoiding:

(1) Overheating and undercutting of the weld metal.

(2) Too high a current setting.

(3) Too long an arc.


a. The weld should be of consistent width throughout. The two edges should form straight parallel lines.

b. The face of the weld should be slightly convex with a reinforcement of not more than 1/16 in. (1.6 mm) above the plate surface. The convexity should be even along the entire length of the weld. It should not be high in one place and low in another.

c. The face of the weld should have fine, evenly spaced ripples. It should be free of excessive spatter, scale, and pitting.

d. The edges of the weld should be free of undercut or overlap.

e. Starts and stops should blend together so that it is difficult where they have taken place.

f. The crater at the end of the weld should be filled and show no holes, or cracks.

(1) If the joint is a butt joint, check the back side for complete penetration through the root of the joint. A slight bead should form on the back side.

(2) The root penetration and fusion of lap and T-joints can be checked by putting pressure on the upper plate until it is bent double. If the weld has not penetrated through the root, the plate will crack open at the joint as it is being bent. If it breaks, observe the extent of the penetration and fusion at the root. It will probably be lacking in fusion and penetration.


a. Lack of Penetration. Lack of input in the weld area. This can be penetration is the result of too little heat corrected by:

(1) Increasing the wire-feed speed and reducing the stickout distance.

(2) Reducing the speed of travel.

(3) Using proper welding techniques.

b. Excessive Penetration. Excessive penetration usually causes burnthrough. It is the result of too much heat in the weld area. This can be corrected by:

(1) Reducing the wire-feed speed and increasing the speed of travel.

(2) Making sure that the root opening and root face are correct.

(3) Increasing the stickout distance during welding and weaving the gun.

c. Whiskers. Whiskers are short lengths of electrode wire sticking through the weld on the root side of the joint. They are caused by pushing the electrode wire past the leading edge of the weld pool. Whiskers can be prevented by:

(1) Reducing the wire-feed speed and the speed of travel.

(2) Increasing the stickout distance and weaving the gun.

d. Voids. Voids are sometimes referred to as wagon tracks because of their resemblance to ruts in a dirt road. They may be continued along both sides of the weld deposit. They are found in multipass welding. Voids can be prevented by:

(1) Avoiding a large contoured crown and undercut.

(2) Making sure that all edges are filled in.

(3) On succeeding passes , using slightly higher arc voltage and increasing travel speed.

e. Lack of Fusion. Lack of fusion, also referred to as cold lap, is largely the result of improper torch handling, low heat, and higher speed travel. It is important that the arc be directed at the leading edge of the puddle. To prevent this defect, give careful consideration to the following:

(1) Direct the arc so that it covers all areas of the joint. The arc, not the puddle, should do the fusing.

(2) Keep the electrode at the leading edge of the puddle.

(3) Reduce the size of the puddle as necessary by reducing either the travel speed or wire-feed speed.

(4) Check current values carefully.

f. Porosity. The most common defect in welds produced by any welding process is porosity. Porosity that exists on the face of the weld is readily detected, but porosity in the weld metal below the surface must be determined by x-ray or other testing methods. The causes of most porosity are:

(1) Contamination by the atmosphere and other materials such as oil, dirt, rust, and paint.

(2) Changes in the physical qualities of the filler wire due to excessive current.

(3) Entrapment of the gas evolved during weld metal solidification.

(4) Loss of shielding gas because of too fast travel.

(5) Shielding gas flow rate too low, not providing full protection.

(6) Shielding gas flow rate too high, drawing air into the arc area.

(7) Wrong type of shielding gas being used.

(8) Gas shield blown away by wind or drafts.

(9) Defects in the gas system.

(10) Improper welding technique, excessive stickout, improper torch angle, and too fast removal of the gun and the shielding gas at the end of the weld.

g. Spatter. Spatter is made up of very fine particles of metal on the plate surface adjoining the weld area. It is usually caused by high current, a long arc, an irregular and unstable arc, improper shielding gas, or a clogged nozzle.

h. Irregular Weld Shape. Irregular welds include those that are too wide or too narrow, those that have an excessively convex or concave surface, and those that have coarse, irregular ripples. Such characteristics may be caused by poor torch manipulation, a speed of travel that is too slow, current that is too high or low, improper arc voltage, improper stickout, or improper shielding gas.

i. Undercutting. Undercutting is a cutting away of the base material along the edge of the weld. It may be present in the cover pass weld bead or in multipass welding. This condition is usually the result of high current, high voltage, excessive travel speed, low wire-feed speed, poor torch technique, improper gas shielding or the wrong filler wire. To correct undercutting, move the gun from side to side in the joint. Hesitate at each side before returning to the opposite side.


a. Burn-Through. Burn-through may be caused by the following:

(1) Current too high.

(2) Excessive gap between plates.

(3) Travel speed too s1ow.

(4) Bevel angle too large.

(5) Nose too small.

(6) Wire size too small.

(7) Insufficient metal hold-down or clamping.

b. Crown Too High or Too Low. The crown of the weld may be incorrect due to the following:

(1) Current too high or low.

(2) Voltage too high or low.

(3) Travel speed too high.

(4) Improper weld backing.

(5) Improper spacing in welds with backing.

(6) Workpiece not level.

c. Penetration Too Deep or Too Shallow. Incorrect penetration may be caused by any of the following:

(1) Current too high or low.

(2) Voltage too high or low.

(3) Improper gap between plates.

(4) Improper wire size.

(5) Travel speed too slow or fast.

d. Porosity and Gas Pockets. These defects may be the results of any of the following:

(1) Flux too shallow.

(2) Improper cleaning.

(3) Contaminated weld backing.

(4) Improper fitup in welds with manual backing.

(5) Insufficient penetration in double welds.

e. Reinforcement Narrow and Steep-Sloped (Pointed). Narrow and pointed reinforcements may be caused by the following:

(1) Insufficient width of flux.

(2) Voltage too low.

f. Mountain Range Reinforcement. If the reinforcement is ragged, the flux was too deep.

g. Undercutting. Undercutting may be caused by any of the following:

(1) Travel speed too high.

(2) Improper wire position (fillet welding).

(3) Improper weld backing.

h. Voids and Cracks. These weld deficiencies may be caused by any of the following:

(1) Improper cooling.

(2) Failure to preheat.

(3) Improper fitup.

(4) Concave reinforcement (fillet weld).

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