Interpass temperature

Preheat and interpass temperature shall be as specified/qualified per the applicable WPS/PQR. ... 

Maintain interpass temperature between 177X1 and 232X (350X and dSOT). 

The permissible maximum carbon equivalent for butt welds in line pipe using cellulosic (EXX10) electrodes based on minimum preheat and interpass temperature, pipe wall... 

Preheat is not required for grades up to API X52 when the CE is less than 0.5 to 0.55 [by Equation (5.1)]. Equation (5.2) is commonly used in specifications. Limiting the Equation (2) CE to 0.42 for X60 through X70 grades is usually required. The maximum CE, based on preheat and interpass temperature, wall thickness, and heat input (travel speed), can be estimated from Figure 5.10. For example, for 0.42 CE and 1 in. (25 mm) wail pipe, a preheat of 68° F (20° C) would be required for a 12 KJ/cm heat input however, if the heat input was reduced to 9 KJ/cm, then a 140 F (60° C) preheat would be required. 

It may also be necessary to decide limitations on the level of preheat and interpass temperature which can be used for example, welding manually within an enclosed space may preclude high temperatures. 

With procedures of this type no control of weld bead size is normally necessary. However, when conditions are severe (for example, high carbon content, thick plate, or high restraint levels) there is some advantage in producing relatively small beads. These require little time at the interpass temperature for much of their... 

At low hardness values (below about 450 HV), low preheat and interpass temperatures are predicted and postweld heating may not be necessary. A further reduction of temperature may be possible if very low hydrogen processes can be used, but this should be confirmed by joint simulation tests. For example, in maraging steels graded M and having a maximum carbon content of 0.02%, Fig. 

Nonetheless, an approximate and conservative estimate of the hydrogen loss during the time taken to make the weld can be made by calculating the amount lost from an individual weld bead during the 10 min interpass time at the interpass temperature of 250 °C. 

In welding procedures it is possible to specify a minimum and/or a maximum interpass temperature. 

The application of heat to a weld, immediately after welding and before cooling out, so as to maintain the minimum interpass temperature, or to raise it to some higher value, in order to increase the rate of diffusion of hydrogen out of the weldment. 

PWHT or radiography depends upon carbon content, grade of material, type of welding, thickness, preheat and Interpass temperatures, and types of electrodes. See ASME Code, Section VIII, Div. 1 Table UHA-32, and paragraphs UHA 32 and 33 for concessions/restriclions. 

Paragraph C.l.b implies that the qualification materials are an infinite heat sink that would instantaneously dissipate the heat input from the welding process. The qualification procedure consists of starting the welding at the minimum preheat temperature. Welding is continued until the maximum interpass temperature is reached. At this time, the test material is permitted to cool to the minimum preheat temperature and the welding is restarted. Preheat temperatures utilized for low alloy steel are in accordance with Section III of the ASME Code. The maximum interpass temperature utilized is 500°F. 

PWHT or radiography depends upon carbon content, grade of material, type of welding, thickness, preheat and interpass temperatures, and types of electrodes. See ASME Code, Section VIII, Div. 1 Table UHA-32, and paragraphs UHA 32 and 33 for concessions/restrictions. Radiography shall be performed after PWHT when required. 100% R.T. is required for all vessels in lethal service (ASME Code UW-2(a)). Materials requiring impact testing for low temperature service shall be PWHT (ASME Code, UCS-67 c)). 

Third, overheating and embrittlement by excessive grain growth in the weld and HAZ should he avoided by minimizing heat input. In multi-pass welds, overheating and embrittlement should he avoided by keeping the interpass temperature helow 95 °C (200 °F). 

In addition, if there were no restriction on maximum interpass temperature, the heat produced by previous weld passes could be used to decrease the cooling rate further in the critical temperature range above about 1000 °C (1830 °F). Preliminary tests with preheated work pieces have shown the significance of temperature in suppressing Cr-N precipitation. Currently, the maximum recommended interpass temperature for Alloy 2205 is 150 °C (300 °F). 

This temperature fimit does not appear to be critical, and it is suggested that this limit could be increased to 300 °C (570 °F). The maximum recommended interpass temperature for Ferralium Alloy 255 is 200 °C (390 °F). Excessive grain growth as a result of too much heat input must also be considered to avoid loss of ductility and impact toughness. 

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