Determining the alternate minimum preheat and inter-pass temperaturerequirements in accordance with “Annex XI Guideline on Alternative Methods for Determining Preheat” For Panyu Thick Material welding. I. Synopsis: This write up is to determine the alternate minimum preheat and inter-pass temperature requirements in accordance with “Annex XI Guideline on Alternative Methods for Determining Preheat” For Panyu Thick Material welding. The methods of Annex XI are based on laboratory cracking tests and may predict a more realistic preheat temperatures with due consideration on many other factors that may reduces the tendency for cold cracking. II. Introduction: The principle of applying heat until a certain temperature is reached and then maintaining that temperature as a minimum is used to control the cooling rate of weld metal and adjacent base metal. The higher temperature permits more rapid hydrogen diffusion and reduces the tendency for cold cracking. The entire part or only the metal in the vicinity of the joint to be welded may be preheated (see Table 3.2). For a given set of welding conditions, cooling rates will be faster for a weld made without preheat than for a weld made with preheat. The higher preheat temperatures result in slower cooling rates. When cooling is sufficiently slow, it will effectively reduce hardening and cracking. The minimum preheat or inter-pass temperature applied to a joint composed of base metals with different minimum preheats from Table 3.2 (based on Category and thickness) shall be the highest of these minimum preheats. It should be emphasized that temperatures in Table 3.2 are minimum temperatures, and preheat and inter-pass temperatures must be sufficiently high to ensure sound welds. The amount of preheat required to slow down cooling rates so as to produce crack-free, ductile joints will depend on: (1) The ambient temperature (2) Heat from the arc (3) Heat dissipation of the joint (4) Chemistry of the steel (weldability) (5) Hydrogen content of deposited weld metal (6) Degree of restraint in the joint Point 1: Point 2: Point 3: is considered above. is not presently considered in the code. is partly expressed in the thickness of material. III.2. Determine carbon and carbon equivalent: . Accepted methods of prediction or guidelines such as those provided in Annex XI.2 may be safely relaxed. Welding of Panyu 4-2/5-1 Jackets. Two methods are used as the basis for estimating welding conditions to avoid cold cracking: Heat-affected zone (HAZ) hardness control Hydrogen control Determining the type of control. WPS qualification in conformance with section 4 shall be required.2. hydrogen level or lower welding heat input where higher preheat may be warranted.Point 4: Point 5: Point 6: is expressed indirectly in grouping of steel designations. is least tangible and only the general condition is recognized in the provisions of Table 3.2. may be used. and the emphasis on preheat and inter-pass temperatures as being minimum temperatures assumes added validity. or other methods approved by the Engineer. should the use of these guidelines result in preheat temperatures lower than those of Table 3. the requirements of Table 3. minimum preheats and inter-pass temperature may be established on the basis of steel composition. optionally. The guide may be of value in identifying situations where the risk of cracking is increased due to composition. Material: GB712-2000 D40 Thickness: 90mm IV. is presently expressed either as non-low hydrogen welding process or a low hydrogen welding process. Alternatively. Based on these factors. The methods of Annex XI are based on laboratory cracking tests and may predict preheat temperatures higher than the minimum temperature shown in Table 3. The following procedure is suggested as a guide for selection of either the hardness control or hydrogen control method. restraint. the guide may assist in defining conditions under which hydrogen cracking is unlikely and where the minimum requirements of Table 3. Method.2 should not be considered all encompassing. Recognizing the above. However. i.024 CE= 0.220+0. a minimum energy to control hardness and preheat to control hydrogen may be required for both types of welds. . The hardness control method and selected hardness shall be used to determine minimum energy input for single-pass fillet welds without preheat.440+0.. use hydrogen method to determine preheats.060+0.e.Carbon Content= 0. If the energy input is not practical.0286+0. Zone II. fillet and groove welds.143 CE = 0. For steels with high carbon. the hydrogen control method shall be used to determine preheat.022+0.270)/6+(0.4806 The material can be classified as Zone II Material.285+0.143+0. Both control methods are considered.140)/15 CE = 0.143+(1. For groove welds.061)/5+(0. The critical cooling rate was determined for a selected maximum HAZ hardness of between 400 Vh . Determining the R450 Critical Cooling Rate. (Root pass/Tack Welding) (The hardness control method and selected hardness shall be used to determine minimum energy input for single-pass fillet welds without preheat. This is achieved by controlling the cooling rate below a critical value dependent on the hardenability of the steel.) This method is based on the assumption that cracking will not occur if the hardness of the HAZ is kept below some critical value. The critical cooling rate R450 for HAZ hardness of 350HV-450HV is 30’C/S .350 Vh from Figure XI-2.Hardness Control. With the said cooling rate. (In practice equivalent to root pass) for various combination of WebFlange thickness are calculated as in following: . the minimum energy input for single-pass SAW fillet welds without preheats. . . 85KJ/ mm. .For the hardness control method. the calculated minimum heat input for SAW SinglePass Fillet weld welding is 1. 3: Welding Process SAW SMAW GMAW.Following may be used to determine fillet sizes as a function of energy input. For other processes. Therefore the required approximate Leg-Size for Single Pass SAW Fillet or equivalent tack weld size is 10mm.1. FCAW Multiplication Factor 1 1. minimum energy input for single-pass fillet welds can be estimated by applying the following multiplication factors to the energy estimated for the submerged arc welding (SAW) process in XI6.25 .50 1. .Therefore the required approximate Leg-Size for Single Pass SMAW Fillet or equivalent tack weld size is 12mm. 140+0. For the type of electrode and site control the electrode hydrogen level may be classified as H2 Low Hydrogen.270/30+(1.) The hydrogen control method is based on the assumption that cracking will not occur if the average quantity of hydrogen remaining in the joint after it has cooled down to about 120’F (50’C) does not exceed a critical value dependent on the composition of the steel and the restraint. or wire/flux combination used. (For groove welds.006 Pcm = 0.2387 . which is defined as: H2-Low Hydrogen.220)/60+(0. Electrode.Hydrogen Control.4% maximum in accordance with AWS A5.061)/10+5x0 Pcm = 0.2.0757+0.143+0.3. brand of consumable. The following may be assumed to meet this requirement: (a) Low-hydrogen electrodes taken from hermetically sealed containers conditioned in accordance with 5. or moisture content of electrode covering of 0.001+0.009+0.1.004+0. This may be established by a test on each type.022)/15+(0.1 of the code and used within four hours after removal (b) (b) SAW with dry flux Pcm Composition Parameter Pcm = 0. the hydrogen control method shall be used to determine preheat.143+0. These consumables give diffusible hydrogen content of less than 10 ml/100g deposited metal when measured using ISO 3690-1976.440+0.060)/20+(0. .The susceptibility index grouping from Table XI-1 can be determined to be “D” From Table XI-2 for Hydrogen Control. Assuming medium and high levels of restraint. it gives the minimum preheat and inter-pass temperatures that shall be used. The required preheat and inte-rpass temperature shall be 145’C. 2. . 2. For the hardness control method. 3. a minimum preheat and inter-pass temperatures assuming medium and high levels of restraint the required preheat and inter-pass temperature shall be 150’C. (150’C) Summarizing: 1.Code recommended pre-qualified minimum preheat and inter-pass temperature. The required approximate Leg-Size for Single Pass SAW Fillet or equivalent tack weld size without preheats is 10mm. the calculated minimum heat input for SAW Single-Pass Fillet weld without preheat is 1. The required approximate Leg-Size for Single Pass SMAW Fillet or equivalent tack weld size without preheats is 12mm 4. higher of calculated and Table 3.85KJ/ mm. For Hydrogen Control. 12mm minimum effective weld thickness should be specified. Conclusion: 1. . 3. Minimum preheat and inter-pass temperature shall be 150’C 4. 2.V. For Submerge Arc Welding tack welds without preheat. Method of welding consumable control. 10mm minimum effective weld thickness should be specified. (2) and (3) are strictly adhered. 2. The material may be concluded that it can be welded with little risk of cracking if (1). Further discussion/investigation required: 1. Pre-heating method and heat maintenance. For Shield Metal Arc Welding tack welds without preheat.
Report "AWS D1.1 Determining the Minimum Preheat -Blank"