The problem of not having applied the required preheating temperature is not the appearance of welding defects (or discontinuities, a more precise word), but the residual stresses that the weld will contain and/or the distortion (warpage) that the welded metal may show up.
According to the chemical composition of the plate (carbon or alloy steel) you will have to carry out the required PWHT (post weld heat treatment).
Giovanni S. Crisi
Sao Paulo - Brazil
P.S. Just in case you don't know, all defects are discontinuities, but not all the discontinuities are defects. Discontinuities don't require to be removed and remake the weld; defects do.

Depending on the following issues preheat may not be required:
Type of metal
Temperature that they were welded at
Process used
Consumable used
Joint design

The reason that these three are important is that it may not even require much preheat, 40 mm is on the border line of preheat increases in many materials under D1.1. The type of process uses along with the type of consumable used adds to this. If E6010 was used to weld this, you have a problem, if submerged arc was used and several layers were placed right after one another the heat from the welding will keep it pretty warm. Joint design comes into play because some joints are more likely to build up residual stress then others, and if it was backgouged before welding the second side all the better, it removes that cold root pass. Also if the weld is in compression and not tension that will help.

To correctly answer your question would need the above information, but 100% UT after waiting a few days to see if there is any hydrogen cracking may be ok especially if the weld is in compression, including RT and MT would even be better, adding a hydrogen bake out would be better still.

Peter Kinney

No.