Frequently Asked Questions
When there is no appropriate national or international standard for fabrication, you will have to invent your own quality standard or use one published for another product which you consider has the same structural duty as your own fabrication.
By 'quality standard', a weld defect acceptance standard is usually meant, and what is appropriate will depend on the stresses and the predicted stress history, as well as on what is regarded as the consequence of failure. For instance, if a dock gate is a conventional small beam and box structure, we may say that in construction and consequence of failure, the gate is analogous to a building and we can look at the applicable standard(s) for buildings. If we judge the fabrication to be more than a simple statically loaded structure, we might look at quality standards for road bridges. If it is a very large structure in which the consequences of failure would be severe, putting people's lives at risk and causing damage to property, then we might seek more demanding standards, such as would be appropriate to a pressure vessel.
If we need more than that, then we have to carry out an Engineering Critical Assessment and derive acceptance standards using fracture mechanics principles as for example in BS 7910 'Guide to methods for assessing the acceptability of flaws in metallic structures'. TWI has a software package - 'Crackwise' - which automates the fracture assessment procedures in BS 7910.
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