All welding defects are developed discontinuities. If a discontinuity renders a weld incompetent or lowers its quality, it would be classified as a defect. Defects make the product risky to use or substandard. It is up to the quality control to decide whether the discontinuity qualifies as a defect or not.
What is the difference between discontinuities and defects in welding?
A discontinuity could be the result of a defect, but isn’t necessarily a defect. A defect, on the other hand, is a discontinuity that by nature or accumulated effect (for example, total crack length) renders a part or product unable to meet minimum applicable acceptance standards or specifications.
What weld discontinuity is most severe?
Cracks – Cracks are the most detrimental discontinuity for the integrity of a welded connection.
What are the weld discontinuities and their causes?
- Porosity. Porosity occurs when gas becomes trapped in the weld pool, forming permanent bubbles as the metal cools from a liquid state back to a solid. …
- Inclusions. …
- Inadequate Joint Penetration. …
- Incomplete Fusion. …
- Arc Strikes. …
- Overlap.
What determines if a discontinuity is acceptable?
Welding Discontinuities Evaluation of the discontinuity will determine if the discontinuity is a defect or an acceptable condition: … Undercut – A groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal.
What is discontinuity material?
A discontinuity is an imperfection or interruption in the normal physical characteristics or structure of a material (e.g. crack, porosity, and inhomogeneity etc.).
Is a discontinuity a defect?
A discontinuity is not necessarily a defect. or product unable to meet minimum applicable acceptance standards or specifications. the term designates rejectability. Engineering Problems?
Do all welds have flaws?
Welds have different susceptibilities to flaws of different types (slag, pores, hydrogen cracks, solidification cracking, liquation cracking, reheat cracking, lack of fusion, lack of penetration etc). Flaws may be associated with an individual bead or, in the case of a multi-pass weld, with the weld itself.How will you prevent the discontinuities and problems of weld?
The most practical methods for controlling or eliminating porosity is to use clean base materials, suitably stored and non-contaminated welding consumables, adequately maintained welding equipment, acceptable environmental conditions, and proven welding procedures.
What is a discontinuity or discontinuities which by nature or accumulated effect?5. What is a defect? • A defect is a “discontinuity or discontinuities that by nature or accumulated effect render a part or product unable to meet minimum applicable acceptance standards or specifications. The term designates rejectability.”
Article first time published onWhy is excessive weld reinforcement bad?
Excess Reinforcement Or Penetration For fillets – is excess weld metal above the specified fillet size including throat thickness. Excess reinforcement/penetration can be caused by excessive current, too slow travel speeds and incorrect joint fit-up.
What causes weld cracking?
The major cause of a crack is when internal stresses exceed the strength of the weld metal, the base metal, or both. And once a focal point for these stresses—that is, a stress riser—develops and accumulates, a crack can propagate.
How do you prevent lamellar tearing?
The choice of material, joint design, welding process, consumables, preheating and buttering can all help reduce the risk of tearing.
What is inherent discontinuity?
Inherent discontinuities are created when metal is molten and malleable during the casting process. … Inherent cast discontinuities are associated with the melting, casting, and solidification of a cast article – or, put simply, the processing of metal, via molding, into a usable shape or form.
What causes porosity?
Porosity is caused by the absorption of nitrogen, oxygen and hydrogen in the molten weld pool which is then released on solidification to become trapped in the weld metal. … As little as 1% air entrainment in the shielding gas will cause distributed porosity and greater than 1.5% results in gross surface breaking pores.
What is lamination in welding?
A lamination seam is part of a weld seam inspection in which the weld seam is overlayed with the lamination material to produce a smooth finish on the weld seam. A lamination seam can protect the weld portion on a metal joint from corrosion.
When should welders perform visual inspection?
page. 1. When – Final visual inspections must be performed: a) When the weld is complete, and in the final sur- face and heat treated conditions b) Before other NDT (when required) c) Before being made inaccessible for inspection 2.
What is underfill in a weld?
Discontinuity; not enough filler metal welded into groove, making the total thickness of the weld less than the total thickness of the base material next to the weld.
What is surface discontinuity?
[¦sər·fəs əv ‚dis‚känt·ən′ü·əd·ē] (fluid mechanics) A surface within a fluid across which there is a discontinuity in fluid velocity; often generated in the wake of a body moving relative to the fluid.
What undercut in welding?
In welding, undercutting is when the weld reduces the cross-sectional thickness of the base metal. This type of defect reduces the strength of the weld and workpieces.
What are the inherent discontinuities found in casting?
Inherent discontinuities are formed during the initial metal making process. Several types of inherent discontinuities exist: inclusions, pipe, cracks and porosity. Inclusions are nonmetallic impurities such as slag, oxides, and sulphides that are present in the original ingot (Figure 3-1).
How do we avoid bad welds?
Prevent this type of weld defect by using the right metal. You’ll need to remove the impurities in your metal and preheat it as required. Additionally, use the proper joint design for the material and properly cool the welded area. Be sure to weld enough sectional areas, too.
How would you avoid electric shock during welding?
To avoid secondary voltage shock, welding operators should wear dry gloves in good condition, never touch the electrode or metal parts of the electrode holder with skin or wet clothing and be sure to insulate themselves from the work and ground, keeping dry insulation between their body and the metal being welded or …
How do you prevent cracks in welding?
Use a preheat on heavier sections of base materials or where there is a large heat-sink to slow the cooling rate, reducing weld shrinkage stress and preventing cracking.
How can you tell if a weld is bad?
Signs of a bad weld include: Underside of weld has insufficient penetration, excessive globules of metal, over-sized weld, undersized welds, undercut, overlap, incomplete fusion, porosity and/or cracking. Excessive grain growth or the presence of hard spots cannot be determined visually.
What kind of defects should not be in good welding?
Gas cavities remaining inside the bead are an internal defect known as blow holes. The causes of these defects include the use of improper shielding gas; insufficient deoxidizer; oil, rust, plating or other matter adhering to the surface of the groove in the base material; and moisture contained in the material.
What are the five essential of welding?
Travel speed is influenced by the type of welding current (DCEN, DCEP or AC), amperage, welding position, electrode melt rate, material thickness, surface condition of the base metal, type of joint, joint fit up and electrode manipulation.
Which of these is a discontinuity in which the weld face extends beyond the weld toe?
Overlap – This discontinuity is defined as the protrusion of weld metal beyond the weld toe or weld root. This condition can occur in fillet welds and butt joints and can produce notches at the toe of the weld that are undesirable due to their resultant stress concentration under load.
Is a weld discontinuity in which fusion doesn't occur between the weld metal and fusion faces or adjoining weld bead?
Incomplete Fusion and Incomplete Joint Penetration Incomplete fusion is a weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads. This absence of fusion may occur at any location within the weld joint and may be present in fillet welds and/or groove welds.
What weld discontinuity shows up as a light region on a radiograph?
Discontinuities in Gas Metal Arc Welds (GMAW) On a radiograph they appear as light, “wire like” indications. Burn-Through results when too much heat causes excessive weld metal to penetrate the weld zone.
Why do my welds look burnt?
Causes: Excessive heat is the primary cause of burn through. Having too large of a root opening on the weld joint can also result in burn through. … Increasing travel speed helps, too, especially when welding on aluminum, which is prone to heat build-up.
