EWF - TECHNICAL SHEET - CALCULATION OF PREHEAT TEMPERATURE FOR BUTT WELDS

Pre-heating temperature for butt welding

Fundamentals of preheatingPreheating involves heating the base metal,either in its entirety or just the regionsurrounding the joint, to specifictemperature, The preheat temperature.Heating may be continued during the

ldi b t f tl th h t

Heat InputIt can be see that an increase of heat input(Q) during welding permits a reduction ofpreheat temperature.

welding process, but frequently the preheatform's sufficient to maintain the desiredtemperature through out the weld.

Hydrogen scaleThe hydrogen scale to be used for any arcwelding process depend mainly on the

Calculation of preheat temperatureThe effect of chemical compositioncharacterized by the carbon equivalent(CET) ,the plate thickness (d),the hydrogencontent of the weld metal (HD), and heatinput (Q) can be combined by the formulagiven below to calculate the preheatg p p y

diffusible hydrogen content.The effect of hydrogen content, HD, of theweld metal in accordance with ISO3690 onpre-heat temperature can calculate using thefollowing expression:

given below to calculate the preheattemperature:

Graphical determination of preheattemperature

Combined thicknessWhen heating a joint to be welded, theEN1011 code requires that the combinedthickness should be determined as the sum

The relationship between preheattemperature and plate thickness, forselected heat input and carbon equivalentcan be represented:

e (º

c)

of parent metal thicknesses averaged over adistance of 75 mm from weld line.

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Base materialThe influence of the chemical compositionon the cold cracking behavior of steel ischaracterized by mean of carbon equivalent(CET).The effect of carbon and otherindividual alloying element is given by

If the carbon equivalent and heat input inthe diagram do not agree with the actualvalues, the inferred preheat temperatureshall be corrected A correction of 7 5ºC has

Legend: 1-preheat temperature 2-plate thickness

plate thickness (mm)

individual alloying element is given by shall be corrected. A correction of 7.5 C hasto be made for every 0.01% difference incarbon equivalent. The correction for heatinput can obtained in expression notedbefore.