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Fatigue Properties of Welded Joints Related to Specified Quality Levels
in Shop Fabrication
64th Annual Assembly and International Conferenceof the International Institute of Welding
17-22 July 2011, Chennai India
A. F. Hobbacher Jade Univ. of Appl. Sciences, Wilhelmshaven Germany
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Why do we need weld quality ??
Big desasterfrom a smalldetail
Lack of fusionin importantweld
(Thiruvalluvar)
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Possible failure modes
A welded component can wrecked in multiple ways:
1. Plastic collapse due to overload2. Brittle fracture3. Elastic collapse (all types of buckling)4. Creep due to high temperatures5. Wear due to friction6. Corrosion7. Fatigue
Besides corrosion, about 75% of all failures are caused byfatigue. So, a weld quality code should primarily considerthe effects of weld imperfections on fatigue.
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Codes for weld quality assurance
Old German DIN 8563:
Code for understandingbetween welders in shopand inspection personnel.
Five levels: A, B, C, D, E
Basis of ISO 5817:
Now for quality assurance.
Quality Groups B, C, D
Collection of experimental dataand fracture mechanicscalculations.
Compiled in BS PD 6493
later BS 7910
IIW Fatigue Recommendationswidely based on BS 7910
Application codes for differentareas of industry?
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Fatigue classes FAT for design
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Example 1: Angular misalignment
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Example 2: Porosity
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Example 3: Slag inclusions Fatigue properties of slag inclusions up to 10 mm long
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Evaluation of porosity and slag inclusions
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Evaluation of undercut
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Matching imperfections and fatigue
Example for matching ISO 5817 quality groups and fatigue classFAT for 10 mm wallthickness and 5 mm fillet weld throats
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Quality groups and fatigue class 1
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Quality groups and fatigue class 2
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Poposal for ISO 5817
The proposal for the future is that
each quality group correspond to the same fatigue resistance
Example:
quality group B >> at least FAT 90, which is a good butt weld
quality group C >> at least FAT 63, which is the toe of a fillet weld
quality group D >> at least FAT 40, wich is the root of a fillet weld
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Quality groups and fatigue - butt welds
19 types of imperfections in group B result in fatigue classFAT 90only 8 types need a modification to result in fatigue class FAT 90
1. Continuous undercut2. Single pore3. Clustered porosity4. Slag inclusions5. Metallic inclusions6. Linear misalignment of circumferential welds7. Multiple imperfections in longitudinal direction8. Angular misalignment (not in actual version of ISO 5817
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Quality groups and fatigue - fillet welds
17 types of imperfections in group D result in fatigue class FAT 63for weld toe failure and FAT 40 for weld root failure.
Only 5 types need a modification to result in the proposed fatigueclass.
1. Clustered porosity2. Slag inclusions3. Lack of fusion4. Lack of penetration5. Multiple imperfections in logitudinal direction
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