terminologies used in welding

8/10/2019 terminologies used in welding

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PRESENTED BY JISHNU.SPRADEEP KUMAR


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Important Terminologies used in Critical WeldingOperation PreheatingPost Heating or DehydrogenationIntermediate Stress leavingInter pass TemperaturePost Weld Heat Treatment Welding Terminologies used in Qualifications Heat In Put

Heat Effected Zone

HAZ Dilution Overlap In Weld Overlay Tempering Bead


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Preheating

Post Heating or DehydrogenationIntermediate Stress leavingInter pass TemperaturePost Weld Heat Treatment


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Heating the base metal along the weld joint to apredetermined minimum temperatureimmediately before starting the weld.

Heating by Oxy fuel flame or electric resistant coilHeating from opposite side of welding whereverpossibleTemperature to be verified by thermo chalks priorto starting the weld


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Preheating eliminates possible cracking of weldand HAZ

Applicable toHardenable low alloy steels of all thicknessCarbon steels of thickness above 25 mm.Restrained welds of all thickness

Preheating temperature vary from 75 C to 200 Cdepending on hardenability of material,thickness & joint restraint


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Preheating promotes slow cooling of weld and HAZSlow cooling softens or prevents hardening of weld

and HAZSoft material not prone to crack even in restrainedcondition


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Raising the pre heating temperature of the weld jointto a predetermined temperature range (250 C to350 C) for a minimum period of time (3 Hrs) beforethe weld cools down to room temperature.

Post heating performed when welding is completedor terminated any time in between.Heating by Oxy fuel flame or electric resistant coilHeating from opposite side of welding whereverpossibleTemperature verified by thermo chalks during theperiod


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Post heating eliminates possible delayed cracking of weldand HAZ Applicable to

Thicker hardenable low alloy steels

Restrained hardenable welds of all thicknessPost heating temperature and duration depends onhardenability of material, thickness & joint restrain


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Hydrogen is intoduced during welding.

Entrapped hydrogen in weld metal induces delayedcracks unless removed before cooling to roomtemperature

Retaining the weld at a higher temperature for a longerduration allows the hydrogen to come out of weld


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Heat treating a subassembly in a furnace to apredetermined cycle immediately on completion of criticalrestrained weld joint / joints without allowing the welds togo down the pre heat temperature. Rate of heating,Soaking temperature, Soaking time and rate of coolingdepends on material quality and thickness Applicable to

Highly restrained air hardenable material


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Restrained welds in air hardenable steel highly prone tocrack on cooling to room temperature.

Cracks due to entrapped hydrogen and built in stress

Intermediate stress relieving relieves built in stresses

and entrapped hydrogen making the joint free fromcrack prone


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The temperature of a previously layed weld beadimmediately before depositing the next bead over itTemperature to be verified by thermo chalk prior to

starting next bead Applicable to

Stainless SteelCarbon Steel & LAS with minimum impact


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Control on inter pass temperature avoids over heating,there by

Refines the weld metal with fine grainsImproves the notch toughness propertiesMinimize the loss of alloying elements in weldsReduces the distortion


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Heat treating an assembly on completion of all applicable welding, in an enclosed furnace with controlledheating/cooling rate and soaking at a specific temperaturefor a specific time. Rate of heating, Soaking temperature, Soaking time andrate of cooling depends on material quality and thickness Applicable to

All type of CS & LAS


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Welded joints retain internal stresses within the structureHAZ of welds remains invariably hardenedPost Weld Heat Treatment relieves internal stresses andsoftens HAZ. This reduces the cracking tendency of theequipment in service


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Heat In Put

Heat Effected Zone HAZ Dilution Overlap In Weld Overlay Tempering Bead


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It is a part and parcel of weld joint It is inevitable It has properties different from BM & Weld Metal

Weld Zone

HAZDiluted BM

Diluted BM

Weld Zone

Fusion Line


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In all Fusion welding, a small portion of BM very close to the welding heat gets melted andadded to weld zone / fusion zone. Dilution isthe ratio of molten base metal volume (Area)to the volume ( Area) of total fusion zone

HAZ

Diluted BM

Weld / Fusion Zone

Fusion Line

% Dilution = (Area of Diluted BM Total Fused Area) 100


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Weld metal chemistry changes depending on

the extent of dilution Chemical elements influence Physical

properties of the joint. Weld chemistry influences corrosion

resistance of weld overlays

Weld Zone

HAZDiluted BM

Diluted BM

Weld Zone

Fusion Line


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The extent of covering or over lapping of previous weldbead by the adjacent bead.

40 to 50 % Over Lap 10 to 15 % Over Lap

Less Dilution More DilutionMore Thickness

Less Thickness


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Overlap of 40 to 50% results in Less Dilution & more weldoverlay Thickness per layerLess dilution results weld metal chemistry more towardsfiller metal chemistry

40 to 50 % Over Lap 10 to 15 % Over Lap

Less Dilution More DilutionMore Thickness

Less Thickness


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In a multi pass groove & Fillet Welds, each bead & itsHAZ are getting tempered (heat treated) by the welding heat of the next bead.

Thus all beads & their HAZ, except those in last layer ,are tempered.Temper beads are the specially & carefully weldedtemporary beads on the top of final weld

reinforcement with out allowing to generate any HAZ within the BM. Temper beads are to be ground flush with the required reinforcement.


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Temper Bead T1 & T2 Not To Generate HAZ In BMTemper Beads To Be Ground Flush

T2T1

21

33

4 455

T1 & T2 To be ground Flush

HAZ

Rqd. Reinforcement


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terminologies used in welding

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