Gate valves are used in various configurations in natural gas applications, including upstream production facilities, midstream transportation pipelines, and downstream distribution networks. They provide a way to isolate sections of the pipeline for maintenance, repair, or safety reasons. This isolation capability is paramount in emergency situations or during scheduled inspections, allowing technicians to safely work on the system without interrupting the entire gas supply.
Scrap steel is melted in a crucible, induction, electric arc or reverberator furnace at 1500° C or 2700°F. The required alloys carbon and silicon, and flux to bind to impurities to create slag are added to the molten iron. The slag is lighter than iron and floats to the top from where it is removed. The molten iron is then poured into a metal ladle with a long handle which is then carried to the sand molds contained in the metal frames and poured through the riser. Green sand has a lower auto-ignition temperature than the temperature of the molten iron allowing the organic material present in the sand to use up all the oxygen present in the mold, preventing oxidation of the manhole cover. Trapped gasses can cause bubbles in the casting.