ASME STP-PT-079:2016 pdf free download

ASME STP-PT-079:2016 pdf free download.LOCAL HEATING OF PIPING: THERMAL ANALYSIS.
The effect of contact resistance must be included to obtain the proper temperature distribution. In the case of the piping healing system. the contact resistance must be included between the heating layer and piping to obtain the physical temperature distribution.
Contact resistance (or conductance I is a function of the contact area beiween two bodies on a microscopic scale. For the pipint system. this contact resistance is a function of the heating element size. element gcomctry. clement layout (pattern), contact pressurc C’tightncss” of the wrap), pipe size, and pipe surface condition (including roughness and cleanliness). Unlike the pipe. the insulation blanket can conform easier to the heating elements, resulting in a different contact resistance.
When solving the CHT problem using CFD, the thermal contact resistance can be directly specified at a contact interface. Values of thermal contact resistance are difticult (or impossible) to determine analytically. and therefore arc typically determined through experimental measurement. For this analysis, the thermal contact resistance value was the “tuning” parameter used to match the computational solution to experimental measurements. Using thermal contact resistance as a tuning parameter allows the heating layer to be treated as uniform, rather than having to include detailed element layouts in the models.
Note that since the actual temperature distribution is a function of the thermal contact resistance, which is a function of the particular heating elements used. the results arc strictly valid only for the exact equipment used for the heat treating experiments. Other heat treating providers, alternative equipment. or alternative designs could impact the thermal resistance, and thus the resulting thermal distribution. It is suggested that the heat treating experiments be repeated using alternate equipment or an alternate provider.
Heat flows from the heating element into the piping and to the insulation via conduction. Heal is then lost to the surroundings via natural convection and radiation. Heat is applied to the system through a prescribed power input governed by a series of temperature probes. These temperature probes correspond to thermocouples used for control zones during PWHT. The power input is then adjusted.
The use of the CFD solver allows the buoyancy-driven flow pattern throughout the system to determine the film coefficients. This is advantageous as the natural Convection heat flow can he directly computed. rather than estimated. In addthon. this allows 3D effects (top vs. bottom vs. sides of piping lobe included. This is important to determine an accurate tcmpcraturc distribution around the weld. During the heat treatment. the surrounding air (especially insidet the pipe will he expected to heat locally, resulting in spatially varying sink temperatures for a steady state analysis. Using CFD-based analysis allows the air temperature to he directly computed, rather than using an estimated (likely unifocm sink temperature. Note that sufficient mesh refinement is required to accurately capture boundary layer convective effects. The y+ value provides a measure of mesh refinement in the boundary layer. It is defined as the distance from the wall normali,ed by the viscous length scale (4j. A value of 50 or less is recommended and a value of 5 or less is highly preferred to ensure boundary layer accuracy. In all cases the y+ value i, significantly less than 50 and only exceeded one at a limited number of points remote from the area of interest
2.3 Calibration Model Cases
Experimental PWHT simulation measurements were taken for two different nominal pipe diameters, eight inch and 14 inch pipes. in four HB configurations for the former and three H13 configurations for the later. For every case the weld was not placed rather the joined pipes were placed with ends abutting. Temperature readings were taken at the), 6,9, and 12 o’clock locations at or near the centerlines on the outside diameter (OD) and inside diameter (IDt and at the 6 and 12 o’clock locations axially along the OD ol the pipe at the edge of the SB. HB. and GCB for every configuration. These configurations can be seen in Appendix A:
and a summary of the cases can be found in Figure 2-5. Temperature measurements were taken as the pipes were heated to a nearly steady state condition and then allowed to cool. For the purposes of the steady state FD calibration ,mxkls. the temperature profiles at steady state were extracted and used exclusively. The extracted profiles can be seen in Figure 2-6.