SR32 第32研究部会 熔接欠陥の非破壊検査による判定基準と熔接強度との関連性に関する研究(第1報) 昭和32年度

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  • SR32 The 32nd Research Committee A Study on the Relationship between Weld Strength and Evaluation Standards of Weld Defects in Non-destructive Testing (Part 1) 1957

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It is of great significance for evaluation of the quality of weld joints to know the influence of weld defects upon the weld strength. Under the present situation lacking any reliably scientific authority, critical judgement to pass or reject a given weld joint in the non-destructive test is made on the basis of temporarily adopted standards. The present Research Committee has devoted its efforts to attainment of authoritative standards for evaluating the results of non-destructive testing, based on sufficiently scientific grounds, by clarifying the relationship between the weld strength of a joint and the non-destructive test results of that joint. 1) Relative capacities of different types of non-destructive inspection to detect weld defects. The technical factors affecting the detecting capacity of three types of inspection - that is, X-ray, ultrasonic, and magnetic particles as applied to inspection of welds have been investigated theoretically as well as experimentally. The conditions essential to realize the best capacity were sought and defined for each type. Then the three types of inspection were actually applied to testing of various joints having different typical flaws ; the images of such flaws in as-weld joints and the ones with the welds finished smooth and the characteristics of detecting capacity were studied. The results revealed the following fact. With respect to detecting power, direct photography by X-ray is the best of all. For reason of simplicity, fluoroscopy by image intensifier is suitable for relatively thin objects ; for thick objects, with X-ray or γ-ray and G. M. tube and with ultrasonic - any of them may be applied with success, magnetic particle testing are highly susceptible to defects lying near to the surface and suitable for detection of qualitative abnormalities. 2) Relation between defects and the strengths, static and impact, of welded structures. To know the relation between defects and strength s, experiments should be made on weld specimens containing different forms of defect in different measures. As a preliminary step to this study, methods were developed to artificially create any defects as desired without causing qualitative change of material as far as possible. They include variation of welding current, spraying of gases during welding ; with impurities scattered on the work to be welded; boring with a drill or grooving with a saw of the first or the second layer of bead and then welding over the area. Preparatory test results with specimens containing such artificial flaws have been published in a report. 3) Relation between defects and fatigue stregth of welded structures. Calibration of fatigue testing machines and stress control while testing are essential for accurately conducting a fatigue test. To this end, an IIW International Standard calibrating equipment for the fatigue testing machines has been constructed; it proved satisfactory in its performance. The results of fatigue tests tend to be statistically scattered. The committee has carried out a statistical study of fatigue strengths of a mild steel plate which constitutes the mother metal of the welds to know the pattern of such scatter. An enormous number of weld joints were fabricated and X-ray inspected ; out of them, 160 fatigue testpieces representing typical kinds and distributions of defects were selected. The tests on these speciments are now under way and the results are not yet available. 4) Investigation of relationship between weld defects of actual ships and mishaps. Preceding this investigation, the weld joints in the hulls of newly-built ships were radiographed in many shipyards, revealing as a result the extent of welding defectiveness. On the other hand, foreign ships were subjected to X-ray test at the time of their docking for repair in order to have information on the extent of defectiveness of welding in them. The results of investigation are going to be published. 5) Formulation of interpretation standards. With reference to formulation of the Inspection Procedure of Welds, the Committee has reached a definite conclusion on the technique to be adopted through the study described under 1). But as the relation with strength has not yet been clarified, judgement standards by which to pass or reject cannot be established. Therefore the report on this subject will be reserved for the next opportunity.

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