API 650 requirement
7.2.1.3 No welding of any kind shall be performed when the surfaces to be welded are wet from rain, snow, or ice; when rain or snow is falling on such surfaces; or during periods of high winds unless the welder and the work are properly shielded. Also, preheat shall be applied when metal temperature is below the temperature required by Table 7.1a and Table 7.1b. In that case the base metal shall be heated to at least the temperature indicated in Table 7.1a and Table 7.1b within 75 mm (3 in.) of the place where welding is to be started and maintained 75 mm (3 in.) ahead of the arc.
API RP 582
Based on AWS D1.1 Aneex H from Table H1 for Hydrogen level H2 and CE upto 0.38, index is F, corresponding value from Table H2, min preheat required is >140 °C for any restraint level
from the below snap shot taken from Nippon steel catalogue for no cracking and consider CE 0.42 preheat will be above 150 °C
Preheat calculator (EN1011-2)
http://www.gowelding.com/weld/preheat/preheatcalc.htm
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