What Is a Welding Defect?
Welding defects refer to defects formed during the welding process at the weld joint. Welding defects include pores, slag inclusions, incomplete penetration, incomplete fusion, cracks, pits, undercuts, and welding knobs. Among these defects, pores and slag inclusions (spots) are volume defects. Slag, unwelded, unfused and cracked are linear defects, which can also be called surface defects. In particular, cracks and unfusion are surface defects. Dimples, undercuts, welding knobs and surface cracks are surface defects. Other defects (including internal buried cracks) are buried defects. [1]
Component edges must be prepared in accordance with regulations, clean, no burrs, no gas cut slag, no grease or paint, except for workshop protective primer.
The joints must be dry.
No matter what kind of welding method is used, welding in low temperature climate (below + 5 ), the following protective measures must be taken to avoid the adverse effects caused by low temperature welding joints (easy to brittle, harden and crack, easy to weld joints) Defects such as eyelets and slag due to rapid cooling and solidification of the weld):
a) Welding in areas not affected by bad weather (such as wind, humidity and airflow);
b) dry welded joints to avoid material shrinkage due to moisture;
c) Preheating of welded joints to slow down the cooling rate of welds after welding;
d) Cover the welds after welding to prevent the welds from cooling rapidly.
e) The minimum temperature for welding is -10 ° C. Take the protective measures indicated.
f) If necessary, preheat the flame slowly and uniformly at a temperature of at least 50 ° C.
1. Appearance defects: Appearance defects (surface defects) refer to defects that can be found on the surface of the workpiece without the aid of instruments. Common appearance defects include undercuts, welding knobs, depressions and welding deformations, and sometimes surface pores and surface cracks. The root of single-sided welding is not welded through.
A. Undercut refers to the depression or groove formed in the base metal part along the weld toe. It is the gap left by the arc that melts the base metal at the edge of the weld without being fully supplemented by the deposited metal. The main cause of undercuts is the high heat of the arc, that is, the current is too large and the speed of the strip is too small. The angle between the electrode and the workpiece is incorrect, the swing is unreasonable, the arc is too long, and the welding sequence is unreasonable. The magnetic bias of the arc during DC welding is also a cause of undercuts. Undercuts can be exacerbated by certain welding positions (stand, cross, and back).
Undercutting reduces the effective cross-sectional area of the base metal and reduces the bearing capacity of the structure. At the same time, it also causes stress concentration and develops into a crack source.
Correcting the operating posture, selecting reasonable specifications, and adopting a good movement method will help eliminate undercuts. When welding fillet welds, using AC welding instead of DC welding can also effectively prevent undercuts.
B. The liquid metal in the welding bead flows to the base material that has not been heated due to insufficient heating or overflows from the root of the weld. After cooling, the metal nodule that is not fused with the base material is the welding bead. Welding specifications are too strong, the electrode melts too fast, the quality of the electrode is not good (such as eccentricity), unstable welding power characteristics and improper operation posture can easily lead to welding knobs. Welds are more likely to form in the horizontal, vertical, and vertical positions.
Welding lump is often accompanied by defects such as unfusion and slag inclusion, which can easily lead to cracks. At the same time, the welding knob changes the actual size of the weld and brings stress concentration. Welding lugs inside the tube reduce its inner diameter, which may cause flow to block.
Measures to prevent welding knobs: Keep the welding seam in the flat welding position, select the specifications correctly, choose non-eccentric electrode, and operate reasonably.
C. Pit Pit refers to the part of the surface of the weld that is lower than the base metal on the surface or back.
The pits are mostly caused by the welding rod (wire) not staying for a short time when the arc is closed (the pits at this time are called arc pits). When standing and horizontal welding, indentations are often generated at the root of the back of the weld.
The dimples reduce the effective cross-sectional area of the weld. Arc craters often have arc crater cracks and crater shrinkage holes.
Measures to prevent pits: Select a welding machine with a current attenuation system, try to use a flat welding position, select appropriate welding specifications, and let the electrode stay in the molten pool for a short time or swing in a ring when the arc is closed to fill the pit.
D. Unsoldered refers to continuous or intermittent grooves on the surface of the weld. Insufficient filler metal is the root cause of underwelding. The specification is too weak, the electrode is too thin, improper transport, etc. will lead to underwelding.
Under-welding also weakens the weld and is prone to stress concentration. At the same time, because the specification is too weak, the cooling rate is increased, and porosity and cracks are easily caused.
Measures to prevent underwelding: increase the welding current and increase the weld on the cover surface.
E. Burn-through Burn-through refers to that during welding, the penetration depth exceeds the thickness of the workpiece, and the molten metal flows out from the back of the weld, forming a piercing defect.
If the welding current is too large and the speed is too slow, the arc will stay in the weld for too long, which will cause burn-through defects. The workpiece gap is too large, and the blunt edge is too small, which is prone to burn-through.
Burn through
According to ISO 5817: 2003, the welds are classified into three levels: B, C, and D based on weld defects
The following table is the standard and range of defect levels of various grades:
.Number | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups | |
D | C | B | |
1 surface defect | | |
1. 1 | 10 0 | crack | | 0,5 | Not allowed | Not allowed | Not allowed | |
1. 2 | 10 4 | Crater crack | | 0,5 | Not allowed | Not allowed | Not allowed | |
1. 3 | 201 7 | Surface stomata | Maximum size of a single air hole Symmetrical weld Fillet welds | 0,5 to 3 | d 0,3 sd 0,3 a | Not allowed | Not allowed | |
Maximum size of a single air hole Symmetrical weld Fillet welds | > 3 | d 0,3 s , a max. 3 mm d 0,3 a , max. 3mm | d0,2s, max. 2mm d0,2a, max. 2mm | Not allowed | |
1. 4 | 202 5 | Open arc crater | | 0,5 to 3 | h 0,2 t | Not allowed | Not allowed | |
> 3 | h 0,2 t , max. 2 mm | h 0,1 t , max. 1 mm | Not allowed | |
1. 5 | 40 1 | Unfused Incomplete fusion | | 0,5 | Not allowed | Not allowed | Not allowed | |
allow | allow | allow | |
Microscopic unfused | |
1. 6 | 402 1 | Insufficient root penetration | Only for single-sided butt welds | 0,5 | Shortage: h 0,2 t , max. 2 mm | Not allowed | Not allowed | |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
1. 7 | 50 1 1 5012 | Cover undercut | For a smooth transition, not a cluster of defects | 0,5 to 3 | Shortage: h 0,2 t | Shortage: h 0,1 t | Not allowed |
> 3 | h 0,2 t , maximum 1mm | h 0,1 t , maximum 0.5mm | h 0,05 t , maximum 0,5mm |
1. 8 | 501 3 | Undercut | To make a smooth transition | 0,5 to 3 | h 0,2 mm + 0,1 t | Shortage: h 0,1 t | Not allowed |
> 3 | Shortage: h 0,2 t , max. 2 mm | Shortage: h 0,1 t , max. 1 mm | Shortage: h 0,05 t , max. 0,5 mm |
1. 9 | 50 2 | Yu Gao is too big (Butt weld) | To make a smooth transition | 0,5 | h 1 mm + 0,25 b, 10mm | h 1 mm + 0,15 b , Up to 7mm | h 1 mm + 0,1 b , 5mm |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
1.1 0 | 50 3 | Overlays are too high (Fillet weld) | | 0,5 | h 1 mm + 0,25 b , 5mm | h 1 mm + 0,15 b , 4mm | h 1 mm + 0,1 b , Up to 3mm |
1. 1 1 | 50 4 | Excess root height | | 0,5 to 3 | h 1 mm + 0,6 b , | h 1 mm + 0,3 b , | h 1 mm + 0,1 b , |
> 3 | h 1 mm + 1,0 b , max. 5mm | h 1 mm + 0,6 b , up to 4mm | h 1 mm + 0,2 b , up to 3mm |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
1.1 2 | 50 5 | Weld transition is too steep | Butt weld | 0,5 | 90 ° | 110 ° | 150 ° |
Fillet welds | 0,5 | 90 ° | 100 ° | 110 ° |
1.1 3 | 50 6 | Weld metal overflow | | 0,5 | Shortage: h 0,2 b | Not allowed | Not allowed |
1.1 4 | 50 9 5 1 1 | Cover surface depression Insufficient root filling | To make a smooth transition | 0,5 to 3 | Shortage: h 0,25 t | Shortage: h 0,1 t | Not allowed |
> 3 | Shortage: h 0,25 t up to 2mm | Shortage: h 0,1 t max. 1mm | Shortage: h 0,05 t max. 0 , 5mm |
1.1 5 | 51 0 | Burn through | | 0,5 | Not allowed | Not allowed | Not allowed |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
1.1 6 | 51 2 | Excessive fillet welds Asymmetry (Excessive solder fillet length) | When symmetrical fillet welds are required | 0,5 | h 2 mm + 0,2 | h 2 mm + 0,15 | h 1,5 mm + 0,15, |
1.1 7 | 51 5 | Root depression | To make a smooth transition | 0,5 to 3 | h 0,2 mm + 0,1 t | Shortage: h 0,1 t | Not allowed |
> 3 | Shortage: h 0, 2 t up to 2mm | Shortage: h 0,1 t max. 1mm | Shortage: h 0,05 t max. 0,5mm |
1.1 8 | 51 6 | Diffuse stomata | Bubbles in the weld formed at the root during crystallization Spongy stomata (eg, lack of gas protection at the root) | 0,5 | Partial permission | Not allowed | Not allowed |
1.1 9 | 51 7 | Missing connector | | 0,5 | Lack The limit depends on the type of defect that occurs at the reignition position | Not allowed | Not allowed |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
1.2 0 | 521 3 | Fillet weld thickness too small | Not suitable for processes requiring greater penetration | 0,5 to 3 | Shortage: h 0,2 mm + 0,1 | Shortage: h 0,2 mm | Not allowed |
> 3 | Shortage: h 0,3 mm + 0,1, max. 2mm | Shortage: h 0,3 mm + 0,1 up to 1 mm | Not allowed |
1.2 1 | 521 4 | Fillet weld thickness is too big | The actual thickness of the fillet weld is too large | 0,5 | allow | h 1 mm + 0, 2 up to 4mm | h 1 mm + 0,15 Up to 3mm |
1.2 2 | 60 1 | Arc point | | 0,5 | Allowed, without affecting the performance of the base material | Not allowed | Not allowed |
1.2 3 | 60 2 | Welding spatter | | 0,5 | Whether it is allowed depends on the actual application, how to plant the material, whether there is a requirement for anti-corrosion protection, etc. |
2 Internal deficiency |
2. 1 | 10 0 | crack | Except for microcracks and crater cracks All kinds of cracks | 0,5 | Not allowed | Not allowed | Not allowed |
2. 2 | 100 1 | Microcrack | Generally found in micro-cracked metallography Crack (50) | 0,5 | allow | Whether it is allowed or not depends on the type of base metal, and more mainly the aggregation of cracks |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
2. 3 | 20 1 1 2022 | Stomata Diffuse stomata (Evenly distributed) | The following conditions and limitations must be met: See Appendix B a1) The maximum area of the defect as a percentage of the area of the projection surface (including cluster defects) Number of welds (volume of weld) | 0,5 | Single layer: 2.5% Multi-layer: 5% | Single layer: 1,5% Multi-layer: 3% | Single layer: 1% Multi-layer: 2% |
a2) The largest area of the defect on the cross section (Including cluster defects) as a percentage of the fracture surface area (applicable only when the welder examination and process qualification are involved in the production area) b) the maximum size of a single air hole Butt weld Flange welds | 0,5 | 2,5 | 1,5% | 1% |
0,5 | d 0,4 s , max. 5 mm d 0,4 a , max. 5 mm | d 0,3 s , max. 4 mm d 0,3 a , max. 4 mm | d 0,2 s , max. 3 mm d 0, 2 a , max. 3 mm |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
2. 4 | 201 3 | Dense stomata | Case 1 ( D > d A2) Case 2 ( D < d A2 = The sum of the area of each stomata group ( A 1 + A 2 + ...) and Comparison of evaluation area area l p × w p (case 1) Reference length l p is 100 mm When D is less than d A1 or d A2, which is the smallest of the two, draw an envelope to enclose A 1 + A 2 Networking as a missing area (case 2) | | | | |
a ) The maximum total area of pores in the missing projection surface Percent of size (including cluster defects) b ) the maximum size of a single air hole Butt weld Fillet welds | 0,5 0,5 | 16% d 0,4 s , max. 4 mm d 0,4 a , max. 4 mm | 8% d 0,3 s , max. 3 mm d 0,3 a , max. 3mm | 4% d 0,2 s , max. 2 mm d 0,2 a , max. 2 mm |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups | |
D | C | B |
2. 5 | 201 4 | Chain stomata | Case 1 (D> d 2) Case 2 (D < d 2) The sum of the area of each hole as a percentage of the area of the evaluation area l p × w p (case 1) When D is less than the minimum diameter of adjacent pores, the two pores Envelope area as the missing area (case 2) | | | | Single layer: 4% Multi-layer: 8% |
The following limit values for defects must be met; see Appendix B a1) The maximum size of defects on the surface (including cluster defects) Note: The diffused air holes in the projection surface depend on the number of welding layers (Volume of weld) a2) The maximum area of pores (including cluster defects) in the fractured section as a percentage of the fracture surface area (applied only in the production area involving welder examination and process assessment | 0,5 | Single layer: 8% Multi-layer: 16% | Single layer: 4% Multi-layer: 8% | Single layer: 2% Multi-layer: 4% |
0,5 | 8% | 4% | 2% |
b) the maximum size of a single air hole Butt weld Fillet welds | 0,5 | d 0,4 s , max. 4 mm d 0,4 a , max. 4 mm | d 0,3 s , max. 3 mm d 0,3 a , max. 3mm | d 0,2 s , max. 2 mm d 0,2 a , max. 2 mm |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
2. 6 | 201 5 2016 | Stripe stomata Electric stoma | Butt weld | 0,5 | h 0,4 s , max. 4 mm l s , maximum 75mm | h 0,3 s , max. 3 mm l s , max. 50mm | h 0,2 s , max. 2 mm l s , maximum 25mm |
Fillet welds | 0,5 | h 0,4 a , max. 4 mm l a , maximum 75mm | h 0,3 a , max. 3mm l a , but max. 50mm | h 0,2 a , max. 2 mm l a , maximum 25mm |
2. 7 | 20 2 | shrinkage cavity | | 0,5 | Allow shortages, But not allowed to the surface Butt weld h 0,4 s , max. 4 mm Fillet welds h 0,4 a , max. 4 mm | Not allowed | Not allowed |
2. 8 | 202 4 | Crater shrinkage | Measure the larger of h or l dimensions | 0,5 to 3 > 3 | h / l 0,2 t h / l 0,2 t , max. 2 mm | Not allowed | Not allowed |
2. 9 | 30 0 301 302 303 | Solid inclusions, Slag inclusion, flow medium inclusion, oxide inclusion | Butt weld | 0,5 | h 0,4 s , max. 4 mm l s , maximum 75mm | h 0,3 s , max. 3 mm l s , max. 50mm | h 0,2 s , max. 2 mm l s , maximum 25mm |
Fillet welds | 0,5 | h 0,4 s , max. 4 mm l a , maximum 75mm | h 0,3 s , max. 3mm l a , maximum 50mm | h 0,2 a , max. 2 mm l a , maximum 25mm |
2.1 0 | 30 4 | Other than copper Metal inclusions | Butt weld | 0,5 | h 0,4 a , max. 4 mm | h 0,3 a , max. 3mm | h 0,2 a , max. 2 mm |
2.1 1 | 304 2 | Copper | Fillet welds | 0,5 | Not allowed | Not allowed | Not allowed |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups |
D | C | B |
2.12 | 401 40 1 1 4012 4013 | Unfused (Not fully fused) The groove is not fused The inter-layer fused root is not fused | | 0,5 | Allow shortages, but not to the surface Butt weld h 0,4 s , max. 4 mm Fillet welds h 0,4 a , max. 4 mm | Not allowed | Not allowed |
2.1 3 | 40 2 | Not welded | T-joint (fillet weld) | > 0,5 | Shortage: h 0,2 a , max. 2 mm | Not allowed | Not allowed |
T-joint (not fully welded) Butt joint (not fully welded) | 0,5 | Shortage: Butt weld h 0,2 s , max. 2 mm T connector h 0,2 a , max. 2mm | Shortage: Butt weld h 0,1 s , max.1.5 mm Fillet welds h 0,1 a , maximum 1.5 mm | Not allowed |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups | |
D | C | B |
2.1 3 | 40 2 | Not welded | Butt joint (fully welded) | 0,5 | Shortage: h 0,2 t , max. 2 mm | Not allowed | Not allowed |
3.Lack of weld geometry |
3. 1 | 50 7 | Wrong Side | The limit value of the deviation is based on the position without defects. if there is not Specifying other values, the centerline coincides, and only reflects the absence of defects (see Section 1). T refers to a smaller thickness. Wrong edges within the given limits are not treated as cluster defects (see Figures A and B) Figure A: Longitudinal seam | 0,5 to 3 | h 0,2 mm + 0,25 t | h 0,2 mm + 0,15 t | h 0,2 mm + 0,1 t |
> 3 | h 0,25 t , max. 5 mm | h 0,15 t , max. 4 mm | h 0,1 t , max. 3 mm |
Figure B: Loop seam | 0,5 | h 0,5 t , max. 4 mm | h 0,5 t , max. 3 mm | h 0,5 t , max. 2 mm |
Numbering | according to IS O 6520-1 | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups | |
D | C | B |
3. 2 | 50 8 | Angular deformation | | 0,5 | 4 ° | 2 ° | 1 ° |
3. 3 | 61 7 | Fillet weld | Constraints in Section 5 regarding cluster deficiency Close | 0,5 to 3 | h 0,5 mm + 0,1 a | h 0,3 mm + 0,1 a | h 0,2 mm + 0,1 a |
> 3 | h 1 mm + 0,3 a 4mm | h 0,5 mm + 0,2 a Up to 3mm | h 0,5 mm + 0,1 a 2mm |
4 Multiple defects | |
4.1 | no | In any section Multiple defects in cross section at the most unfavourable weld (Macrometallurgical) | | 0,5 to 3 > 3 | Not allowed Maximum total missing height h 0,4 t or 0,25 a | Not allowed Maximum total missing height h 0,3 t or 0,2 a | Not allowed Maximum total missing height h 0,2 t or 0,15 a |
See Appendix A |
Numbering | According to ISO 6520-1 number | Missing name | Explanation | t mm | Limits of defects allowed by different assessment groups | |
D | C | B |
4.2 | no | Projection surface Or longitudinal cross section | Case 1 ( D > l 3) Case 2 ( D < l 3) Sum of surface area hl as percentage of evaluation area l p × w p (case 1) When D is the minimum length of adjacent defects, two defects are connected into one defect (case 2) Note: See Appendix B | 0,5 | h × l 16% | h × l 8% | h × l 4% |
