The NHR-200 reactor in China adopts the noncondensable gas self-stabilizing control and the noncondensable gas used for pressure stabilization control can weaken steam condensation heat transfer in the integrated steam-gas pressurizer. A condensation experimental system was established and the heat transfer characteristics of steam-nitrogen and steam-argon condensation under natural convection had been investigated. The pressure ranged from 0.516 to 5.10 MPa. The distributions of nitrogen and argon in the steam/gas mixture were obtained in the experiments, and the results showed that nitrogen and argon were evenly distributed in the steam under different pressure, respectively. The effects of heat transfer temperature difference had also been investigated and it is found that the total heat transfer coefficient difference had little influence on the total condensation heat transfer coefficient. However, the steam condensation heat transfer coefficient decreased with the increase of the degree of supercooling of the wall. The condensation heat transfer coefficient was reduced by approximately 0.11 kW/(m2·K) as the degree of supercooling of the wall changed from 14°C to 36°C. The condensation heat transfer coefficient also decreased with the mass/molar fraction of noncondensable gas increasing and a certain difference between the effect of the mass fraction of noncondensable gas and the effect of the molar fraction of noncondensable gas was discussed in this paper.

In this article, the welding technology of large diameter thick wall 08Cr9W3Co3VNbCuBN (G115) heat-resistant steel pipes for the main steam pipe of a 650°C ultra-supercritical power station boiler has been investigated, and the mechanical properties and microstructure of welded joints at different wall thickness positions have also been analyzed. The results show that the mechanical properties of narrow gap welded joint of 115 mm thick large diameter 08Cr9W3Co3VNbCuBN heat-resistant steel pipe obtained by Gas tungsten arc welding (GTAW) + shielded metal arc welding (SMAW) + automatic submerged arc welding (SAW) can meet the requirements of relevant standards after tempering at 780°C. The tensile failure of the welded joint occurs in the base metal zone far away from the weld, an obvious necking phenomenon appears at the fracture position, and the welded joint has good tensile properties. No δ ferrite phase was found in the weld and heat-affected zone (HAZ). The microstructures of each zone are tempered martensite.