Unit 4 Weld defects

What types of distortion stresses cause a tee fillet weld to pull the vertical member of the joint toward the side that is being welded/

Angular distortion, Longitudinal or transverse

Underbead cracking occurs most often in what metal?

Carbon steel

What causes dimensional defects?

Cause by improper welding procedure or technique

What it is porosity?

Cavities formed by gases trapped in solidifying metal

If welding a butt weld and the plates are drawn together at the opposite end, what type of distortion is encountered?

Crosswise shrinkage (transverse contraction)

What are dimensional defects?

Longitudinal contraction, transverse contraction, warping and angular distortion

What generally causes cracking in or near a weld?

Low heat and fast cooling rate, shape of bead

What are micro fissures?

Microscopic cracks in welding

describe the difference in appearance of porosity and slag inclusion

Porosity cluster in clumps and appears as elongated holes while slag inclusion have rounded contours

Explain what is meant by a strong back in the control of distortion

Strong backs are stiffeners for the purpose of increasing the resistance to distortion

Angular distortion is greatest on single V-butt welds and least on double V welds T/F?

T

Peening has no control over angular distortion T/F

T

Angular Distortion on V joint, free to move, decreases with the number of passes. T/F

F

Flat beads that are small with deep penetration cause more distortion than beads that are convex? T/F?

F

What are slag inclusions?

Flux appearing in the interior of the weld

Explain why, when welding on single-V and double-U groove welds, the plates will be pulled or warped out of alignment.

Free to move "not restrained", angle of bevel, high heat input, rate of heating

When may cold cracking occur?

It appears usually after weld has solidified "Hours or days after"

What is the purpose of spacing parts prior to welding in the control of distortion?

It will pull the vertical plate into the correct position

Describe incomplete penetration

Lack of fusion between weld metal and base metal

Explain what is meant by prebending in the control of shrinkage or distortion forces

The plates are bent in direction opposite to the side being welded

When does hot cracking usually occur?

When a weld has high temperature and insufficient ductility

Describe lack of fusion

When metal fails to fuse with base metal leaving gaps between base metal and filler metal

List different sequences of welding used to reduce distortional forces

a. Chain intermittent fillet weld b. Staggered intermittent fillet welds c. backstep d. skip stop

List 5 things that may cause cracks in a weld or in a base metal?

a. Craters b. Faulty electrode c. bead shape d. Rigidity e. Fast cooling

3 causes of porosity

a. High sulfur b. current too low c. faulty electrodes

List 3 causes of undercutting

a. Long arcing b. Fast Travel speed c. Excessive welding current

List various factors which affect the shrinkage perpendicular(angular distortion) on butt welds

a. Longer the cross section greater the shrinkage b. angle of bevel c. total heat input d. rate of heating e. peening f. Weld wandering (back step)

List various ways the warpage in a single V and double U groove can be prevented

a. Peening b. Weld alternatively c. time of welding and electrode size

List 3 characteristics of a brittle weld

a. Poor elongation b. very low yield point c. very poor ductility

Write down different ways crosswise or transverse distortion can be controlled

a. Seam of the weld is short b. tack weld c. clamp devices d. pre-spacing

List various factors which affect distortion on fillet welds

a. Shrinkage increases with size of welds b. Shrinkage is proportional to length of weld c. May decrease shrinkage by proper procedure and sequences d. Preheating can help reduce it

Explain the following corrective measures which can be taken if warping has occurred

a. Shrinkage, alternate heating and cooling accompanied by hammering b. Shrink welding, running beads on the convex side of the buckled area c. Added stiffening pulling the plate into line with strong backs and adding more stiffeners

Explain various ways in which longitudinal distortion can be controlled

a. Small weld beads b. proper welding procedure c. Jigs or clamps

List 6 cause of lack of fusion

a. Too fast b. not enough amps c. improper joint penetration d. improper heat e. poor welding technique f. large electrode size

When pre-spacing for the prevention of transverse distortion, what determines the amount of pre spacing used?

a. length of seam b. type of material c. thickness of plate

List 3 ways slag inclusions may be prevented

a. preheat and obtain higher heat input per unit b. Avoid contours that are difficult to penetrate with arc c. Clean each bead

List 6 causes of incomplete penetration

a. too fast b. low current c. unclean metal d. long arc e. joint design faulty f. electrode size too large

list 4 things that can be done to prevent dimensional defects

a. welding jigs b. proper welding sequences c. suitable weld joint design d. preheat and post heat

What type of distortion results from the types of stresses mentioned in t joints

angular distortion

What is the cause of longitudinal distortion?

contraction of the weld reinforcement above weld

undercutting

cutting away at the surface of the weld near the toe of weld

What is one of the principle causes of brittle welds?

excess heat that burns the metal

Why is undercutting such a serious problem?

it invites joint failure by decreasing plate thickness

What is longitudinal distortion?

the weld piece will bow upwards at both ends

How may cracks in a root pass be prevented/

use low hydrogen electrodes, back step to fill craters. Pre-heat or post heat

Is overlap considered a fusion problem?

yes, it is basically a incomplete fusion at the toe of the weld