In the depth of Tarim Basin in Xinjiang, natural gas is transported to all parts of the country through gas transmission pipeline after being exploited and refined. However, due to the corrosion of the pipeline, gas leakage has been repeated. A new gas pipeline made of 2205 duplex stainless steel containing molybdenum is expected to reduce gas leakage and prevent environmental disasters while protecting resources. 4500 tons is the largest single order of duplex stainless steel in China so far.
What is natural gas?
Natural gas refers to all natural gases existing in nature, including gas formed by various natural processes in the atmosphere, hydrosphere and lithosphere (including oilfield gas, gas field gas, mud volcanic gas, coal bed methane and biogenic gas, etc.).
The definition of “natural gas” is a narrow definition from the perspective of energy, which refers to the mixture of hydrocarbon and non hydrocarbon gas naturally contained in the formation. In petroleum geology, it usually refers to oil field gas and gas field gas. It is mainly composed of hydrocarbons and contains non hydrocarbon gases.
Some of the earliest uses of natural gas can be traced back to 500 BC, when the Chinese used hollow bamboo stems to send natural gas into stoves and boil seawater to make salt. Today, China is trying to reduce carbon emissions and get rid of its dependence on coal, so China’s natural gas industry continues to develop. Tarim Basin is one of the largest natural gas reserves in China, and its underground reserves are estimated to be more than 200 trillion cubic feet.
Natural gas production in the vast Gobi
Tarim Basin is located in the most western provinces of China, sparsely populated. In the vast Gobi and the desolate desert, the production and transportation of natural gas is a great feat. Due to the strong wind, the sand is all over the sky, there is no road, and the poor working conditions make drilling, especially the laying and construction of pipelines extremely difficult, time-consuming and expensive.
Natural gas is transported from oil and gas wells to nearby refineries for processing. The balance between natural gas input and refinery capacity is essential to maximize production efficiency. As a result, construction of a new pipeline connecting the two refineries has started. Upon completion, the refinery will be able to direct the inflow of natural gas to optimize capacity utilization.
Finally, the refined natural gas from Tarim Basin enters the west east gas pipeline and is transported to all parts of the country for use.
The new pipeline is located in the orange area of Tarim Basin, Xinjiang, China
Prevent gas leakage
The environmental conditions in Tarim Basin bring many challenges to pipeline operation. The vast desert of Taklimakan has a dry climate. It is hot in summer and cold in winter. Strong wind often forms huge sandstorm, which makes working conditions extremely bad. The soil in this area is highly corrosive and contains a large amount of soluble salt, which is left after evaporation of water all year round. In addition, the carbon dioxide content in natural gas is very high, and it contains up to 10% chloride, which also increases its corrosivity. Under such conditions, only materials with high corrosion resistance can provide a permanent solution.
The pipeline for transporting high corrosive crude natural gas is usually composite steel pipe, that is, carbon steel pipe is lined with 316 stainless steel thin layer. This kind of pipeline can resist the corrosion of corrosive gas and the initial cost is cheaper than the whole stainless steel pipeline. However, it is much more difficult to weld the composite steel pipe on site than in the factory controlled environment. The stainless steel weld in the inner layer will be diluted by carbon steel, which will reduce its corrosion resistance. It has been found that one of the reasons for frequent leakage of natural gas in Tarim Basin is weld corrosion of composite pipeline.
The consequences of natural gas leakage are environmental damage, loss of revenue, and the worst case is explosion, so the leakage must be repaired as soon as possible. However, in this remote desert, finding and repairing the leak is a difficult, time-consuming and even dangerous task. Therefore, the natural gas company for the new pipeline to seek a more durable pipeline material, the first time to prevent the occurrence of leakage.
The pipeline is located in the remote desert area in the West
Molybdenum improves the performance of the pipeline
The new pipeline connecting the two refineries is 3.3 km long, 325 mm in diameter and 406 mm in diameter, with wall thickness ranging from 7 to 17 mm. In order to avoid corrosion completely, engineers chose to use stainless steel as a whole instead of coating or carbon steel clad pipe. The results of literature study and test show that 2205 duplex stainless steel can resist the corrosion of natural gas. Compared with 316 stainless steel, duplex stainless steel with 3% molybdenum content has better pitting and crevice corrosion resistance.
In order to test whether 2205 duplex stainless steel pipeline has enough corrosion resistance to salt desert, a three-year corrosion study was carried out. The test samples buried in sand are inspected every year and the results are satisfactory.
In addition to its excellent corrosion resistance, duplex stainless steel also has other advantages: its excellent strength can make the pipe wall thinner, reduce the weight of the pipeline, so as to facilitate transportation, handling and installation, which is an important consideration under the extreme climate conditions in Tarim Basin. The thinner wall thickness also reduces the time and cost of welding and avoids the complex problems related to the composite pipe.
These advantages mean longer service life and maintenance free, helping to protect the environment and employee safety. Although the initial cost is slightly higher than the clad pipe, the duplex stainless steel solution has a significant impact on reducing the overall cost of natural gas production.
2205 duplex stainless steel piping waiting to be installed on site
Durable solutions
Life cycle costing (LLC) is becoming more and more popular. Material selection is based not only on the initial installation cost, but also on the cumulative cost of future maintenance and operation. Over time, duplex stainless steel pipelines can recover costs by avoiding natural gas loss and eliminating maintenance and replacement costs.
The “pipeline dragon” in Xinjiang not only optimizes the natural gas production in the western region, but also becomes a pioneer in realizing sustainable energy utilization. Investment in the construction of 2205 duplex stainless steel pipeline marks the shift from low cost to more sustainable and lasting solutions.
Source: China Duplex Stainless Steel Gas Pipeline Manufacturer – wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)
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