QIN steel supplied to NES 736 is used extensively in the fabrication of submarines. Traditionally the welding of this steel has been carried out over a 'narrow band' of specified preheat and interpass temperatures, i.e. 120 deg C min. to 150 deg C max. For submarine construction to NES 770 specification, this range had been expanded during the 1990is resulting in the MOD(N) approved range of 70 deg C minimum preheat to 150 degC maximum interpass. The reason BAE Systems introduced such a reduction of preheat temperature was primarily to improve the environmental conditions for the welders working on QIN weldments. There was dose monitoring of the initial production welds carried out with 70 deg C minimum preheat and ongoing weld defect monitoring has indicated that there has been no increase in the incidence of either weld metal or HAZ cracking since the inception of the lower preheat. The reduction of preheat, at this time, was seen as having no detrimental effect on weld metal mechanical properties. There is historical data to show that the maximum interpass temperature of 150 deg C is required to prevent a significant reduction of the weld metal is 0.2% proof stress. Unfortunately such data was not available for present day welding consumables - in particular the new range of wires used in flux cored wire metal-arc welding with active gas shield (FCAW:GS). Such consumables are used in approximately 85% of the submarine QIN structural welds. BAE Systems have therefore embarked on a series of welding development trials the first using a FCAW:GS consumable, namely Safdual 128V. The conclusion that BAE systems have drawn from this welding development test data is that, to maintain a 'comfortable working margin', the current NES 770 specified maximum interpass temperature for QIN welds should remain at 150 deg C.


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    Title :

    Heat trials improve welder conditions


    Contributors:

    Published in:

    Publication date :

    2002


    Size :

    2 Seiten, 1 Bild



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English





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