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Factors to be Considered for Weld Quality

Factors to be Considered for Weld Quality - Weld quality relates directly to the integrity of a weld. It underlies all of the design fabrication and inspection steps necessary to ensure that a welded product will be capable of serving the intended function for the desired life.
Factors to be considered for weld quality are related to :
(i) Design,
(ii) Fabrication,
(iii) Inspection,
(iv) Operation and maintenance,
(v) Economy.

(i) Design
Weld quality includes weld design considerations, which means that each weldment should be :
(a) adequately designed to meet the intended service for the required life,
(b) fabricated with specified materials and in accordance with the design concepts,
(c) handled and maintained properly. The design of a weldment should be consistent with sound engineering practices.
Components of adequate size should be specified to ensure that stresses from anticipated service loads are not excessive. The intended service should be carefully analyzed to determine whether cyclic loading might result in fatigue failure in highly stressed members. Environmental conditions leading to brittle fracture, creep, and corrosion of welds should be considered in the design. Brittle fracture is a possibility in low temperature service and creep is a consideration in high temperature service.

Corrosion and wear can reduce the section size and increase service stresses, as well as create sites for fatigue cracks to initiate and further reduce quality of the weldment.Materials selected for fabricating the weldment should have proper hardness, chemical composition and mechanical properties

Fabrication The fabrication procedures and practices selected should be such that they ensure that the weldment meets the design specifications.; The procedures should be rigorously followed and the weldment should be properly inspected to verify that the base metal and the weld joint are free from unacceptable defects.Majority of welded fabrication standards define quality requirements to insure reasonably safe operation in service.
Inspection Weld quality is verified by non-destructive examination (NDT). The acceptance standards for the welds are generally related to the method of non-destructive examination. All deviations are evaluated and the acceptance or rejection of a weld is usually based on well defined conditions.
Repair of unacceptable or defective conditions is normally permitted so that the quality of the weld may be brought up to acceptance standards.However, they will not tell us if the weld is good enough for our purposes; equally important, they will not guarantee that welds will be made which are free of defects. In other words, we cannot control quality simply by specifying that the welds will be subjected to NDT on completion. Admittedly the knowledge that the welds will be tested may act as an incentive to do better work, but it is far more relevant to establish a system which encourages the production of defect free welds at all times.

Operation and maintenance Operating a welded product safely, requires periodic inspection. If failure at a facility would result in a public hazard or the destruction of property, then inspections should be more frequent and more rigorous. Power plants, chemical plants and refineries, dams, and bridges are examples of fixed facilities that may endanger facility employees, the public, and the surrounding neighborhoods.
Automobiles, trucks, trains, and ships are mobile facilities that may also damage individuals and properties. Maintenance of these facilities is a requirement for continued safe operation. Some facilities can partially continue operations during inspection and maintenance, and others may require a complete shutdown. Often the loss of production is far more expensive than the direct cost of the repair. In such cases, premium materials and. costly fabrication practices can easily be justified, provided these precautions permit extended operating periods between inspections.

  
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