Upstream, Midstream & Downstream Upstream The upstream segment of the industry, often called exploration & production, is traditionally what comes to mind when people think of the oil and gas industry. Companies will search prospective areas for potential reserves of oil and gas and perform geological tests called seismic tests, to determine the size and composition of the resource. Initial wells areoften drilled to "explore" the basin, and if satisfied with results, a companywill enter the production phase to extract the hydrocarbons.
Midstream Often coupled with the downstream segment, the midstream sector involves the transportation, storage and marketing of various oil andgas products. Depending on the commodity and distance covered, transportationoptions can vary from small connector pipelines to massive cargo ships making trans-ocean crossings. While most oil can be transported in its current state, natural gas must be either compressed or liquefied for transport. The midstream sector also includes the storage of oil and natural gas, which balances the fluctuations between supply and demand and helps ensure a secure supply of energy products.
Downstream The downstream sector involves the refining and processing of hydrocarbons into usable products such as gasoline, jet fuel and diesel. Refining is required since "raw" hydrocarbons extracted from the ground are rarely useful in their natural form. The refining process is a complex chemical process that helps separate the hundreds of hydrocarbon molecules into useful forms. Petrochemical plants also break down hydrocarbons into chemical compounds that are used to create a myriad of products ranging from plastics to pharmaceuticals.
1. Reduce the risk of hydrogen crack and martensitic grains structure
2. To eliminate heat affected zone hardness due to sudden cooling cause martensite structure. By pre heating rate of cooling will be less that gives toughness and ductility
-Purpose of the preheat is to remove moisture,slowdown the colling rate to ensure the hydrogen has diffuse out from the weldment.it give the resistance from hydrogen cracking.preheat can be determine by the thickness of the material and carbon equivalent. Interpass temperature means the temperature during welding.the relations between interpass temperature and preheat temperature is when perform welding process, we need to contol the interpass temperature not lower than the preheat temperature and not exceed to the maximum interpass temperature.as example in the wps state that for material F22(low alloy) the preheat temperature 150celcius and the max. interpass tmperature is 270celcius, the welding process should perform in range of the preheat temperature and maximum interpass temperature.if exceed the max. interpass temp. it will induced the problem at the HAZ region.