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Preheat guide SUGGESTIONS FOR PREHEATING STRUCTURAL STEEL Governing codes and standards CSA W AWS D Date of issue Revision No RC Technical Services rctechservices ca - CTABLE OF CONTENTS INTRODUCTION WHY SHOULD WE PREHEAT WHEN SHOULD WE PREHEAT HOW SHOULD

SUGGESTIONS FOR PREHEATING STRUCTURAL STEEL Governing codes and standards CSA W AWS D Date of issue Revision No RC Technical Services rctechservices ca - CTABLE OF CONTENTS INTRODUCTION WHY SHOULD WE PREHEAT WHEN SHOULD WE PREHEAT HOW SHOULD WE PREHEAT MEASURING PREHEAT PREHEAT MINIMUM INTERPASS AND MAXIMUM INTERPASS TEMPERATURE WHERE TO MEASURING PREHEAT SUMMARY Suggestions for Preheating RC Technical Services Page of C INTRODUCTION This guide is not meant to replace the preheat information on CWB or AWS approved Welding Procedure Speci ?cations WPS or Welding Procedure Data Sheet s WPDS Follow the preheat information on approved WPS or WPDS Use this guide at your own risk Follow the information in a CSA W latest revision b AWS D latest revision c AWS approved WPS d CWB approved WPS and or WPDS e Company policies and safe practices Suggestions for Preheating RC Technical Services Page of C WHY SHOULD WE PREHEAT Why should we preheat a It slows the cooling rate which o ?ers more resistance to cracking b The slower cooling rate gives more time for hydrogen to escape reducing the potential for cracking c Reduces shrinkage stresses especially in highly restrained joints d It can help to ensure mechanical properties such as ductility and impact properties WHEN SHOULD WE PREHEAT When should preheat be used a When working to welding codes the minimum preheats must be followed b In some cases higher preheat temperatures may be needed with highly restrained joints or for welding repairs c Thick base metal d Base metal chemistry e Low ambient temperature f Weld metal hydrogen content g Low heat inputs HOW SHOULD WE PREHEAT Choosing the right method for your job whether it be torch heating induction or electrical resistance could make the di ?erence between a successful weld or a costly error a Flame or torch preheating equipment is cheap and is widely used for structural steel Be careful of the ame distance so not to overheat the material in spots When preheating with a torch water will form several inches in all directions from the ame this is a chemical reaction from the gas Water does not come out of steel b Electrical resistance o ?ers more control of the preheat temperature Can be set up and turned on before the shifts starts and be ready for the welders for the start of a shift Equipment is costly thermocouples wires need to be welded on and some weldments can be time consuming to cover c Induction heating is the most costly but seams the easiest to use It heats the steel quicker Water cooled blankets are recommended The setup is very quick Suggestions for Preheating RC Technical Services Page of C MEASURING PREHEAT Preheat can be measured in several ways a Infrared thermometers are cheap and must be calibrated The surface condition of the material will have an e ?ect on the reading Shiny rusty or painted surfaces will give di ?erent readings Read your instructions to determine the best