Present Situation And Development Of Oil Pipeline System

Composition of oil pipeline system

Long distance oil pipeline consists of two main parts: the oil transportation station and the pipeline.

oil transportation station

The starting point of the pipeline is an oil transportation station, known as "the first station", after the crude oil is collected and calculated, the first station provides power to transport to the downstream pipeline. The first station is generally arranged with oil storage tanks, oil pump and oil metering device. Oil pumps provide power to make the oil moved along the pipeline to the terminal or the next level of oil transportation station. Under normal circumstances, due to the long distance, the energy loss of transporting process is obvious, it’s need multilevel oil stations to provide power until crude oil sent to terminal. The end of the oil station known as "terminal station", mainly responsible for collecting material transported from the upstream pipeline, therefore equipped with many tanks and metering system.

Pipeline

Long distance oil pipeline is welded by steel pipe. An insulating layer is wrapped outside the tube to prevent corrosion of the chemical composition in the soil. The internal pipeline can be also coated with anti corrosive material to reduce the corrosion in the transmission of oil and improve the smoothness of the pipeline for large transportation quantity. Every certain distance or across a large obstacle, the pipeline is equipped with a valve to prevent the expansion of the accident and convenient to maintain equipment.

Development Direction

Normal temperature transportation technology

With the increase of the oil production and the exploitation of crude oil to the deep sea, all countries attach great importance to the research on the transportation and flow security technology of waxy oil.

Pipeline monitoring technology

Early warning technology, divided into field type monitoring and sensing monitoring, is becoming a developed pipeline monitoring technology in twenty-first Century. Field type monitoring focus on monitoring people's entry can only be used for a short period of time. Sensing monitoring focus on monitoring can be used for long distance and long time monitoring. These monitoring are affected by various factors, so that they has been subjected by a variety of technical limitations in application. It shows that these monitoring methods need further research.

Some Issues About OCTG Casing And Its Transportation

The classification and function of casing

OCTG casing is a steel pipe supporting oil and gas well wall, which ensures the normal operation of the entire well after the drilling process carried out. Different from tubing and drill pipe, casing can not be repeated use and belongs to a one-time consumption of materials. Therefore, the consumption of the casing pipe accounted for more than 70% of all. According to the situation of use, casing can be divided into: tube, surface casing, technical casing and oil layer casing.

Connection type of casing

Short round thread casing connection type

The short round thread casing is one of the product types in the petroleum casing pipe. Short round thread casing features: 1. Improve resistance caused by abrasion when the thread in the screw. 2. When tightening screw, tooth gap provides a reasonable gap for foreign particles and dirt. 3.The arc tooth top is not sensitive for local scratch or dent damage.

Long round thread casing connection type

Long round thread casing is widely used as a buckle-shaped of oil casing. Due to the thread shape at both ends of the pipe body is like long round, so it’s called long round thread casing. Long round thread has the advantages of easy processing, good sealing performance, strong connection strength and cheap, so it’s widely used in the casing connection.

Buttress thread casing connection type

Buttress thread casing have the name because the thread form is like partial trapezoidal and this thread is widely used in all the thread. The packing of the buttress thread casing is tied up with the steel wire or the steel band. The advantages of this thread improve axial tension and axial compression load and the leakage resistance is also provided.

Casing transporting

• Casing before loading and unloading, the inner and outer screw threads must be tightened by special tools.
• The casing should be hoisted with nylon rope.
• The pipe rack car or wagon should pad sleeper which cross section is 150mm×50mm. If the shipment is more than two layer, the sleeper shall be 300mm×60mm.
• When casing loading, external thread or coupling should be installed one end of vehicles.
• Casing vehicle is strictly prohibited overload, over high.
• You should stop in time to prevent casing loosening and ensure safe transportation in transit.
• Casing should be unloaded from the building root in turn. Control casing running speed, avoiding hit front casing when landing.
• The number of loading casing can not more than 10 roots when using forklift and do it gently to avoid collision.

Coiled tubing, current advanced operation technology in OCTG tubing

OCTG tubing is a pipeline which transports crude oil and nature gas from hydrocarbon reservoir to the surface after the completion of drilling. It’s one of the main products of OCTG and it can withstand the pressure generated in the process of mining. While Coiled tubing technology is the current international advanced operation technology. Coiled tubing is made of low carbon alloy steel pipe and has good flexibility. A roll of coiled tubing is thousands of meters long, which can be used to replace conventional tubing for a lot of work. Coiled tubing operation equipment has the characteristics of pressure operation and continuous up and down.

History of coiled tubing

In 1962, the United States California oil companies and Bowen Oil Tools Company jointly developed the first coiled tubing light workover device. The coiled tubing diameter was 33.4 mm, which  mainly used for sand flushing operation of oil and gas wells in the Gulf of Mexico. 30 years after the birth of the coiled tubing, its value was really understood, to the 1990s, coiled tubing technology has been the development by leaps and bounds. Coiled tubing device has been known as the "universal operating machine", widely used in the oil and gas well workover, drilling, completion, well logging throughout the whole process of the exploitation of oil and gas.

 

The development of the number of coiled tubing equipment is as follows: 1962, the first coiled tubing equipment was born; in the mid-1970s, approximately more than 200; in 1993, about 561; at the beginning of 2001, about 850; at the beginning of 2004, about 1050 units, mainly distributed in North America, South America and Europe; At the beginning of 2011, about 1881, China has 61.

API standard and product specification level(PSL) for pipeline

API standard for pipeline

Line pipe is a dedicated pipe which can transport oil, steam or water to oil and gas industry enterprises. Pipeline includes seamless and welded steel pipe which the ends are flat end, threaded end and the socket end. The connection mode is welding, connection, socket connection and so on.

API is known to everyone in the steel industry and it has long been inscribed in the hearts of every person in the steel tube. API refers to the American Petroleum Institute, while API 5L is the production execution standard of pipe line.

API 5L pipe production is currently using micro alloy heating treatment process. The production costs of seamless stainless steel pipe are significantly higher than the welding pipe and with the increase of steel grade, the limit of carbon content is more and more strict. At present, all the major manufacturers carry out research work in order to improve the corrosion resistance of the pipeline and ensure the stable performance in low and high temperature.

PSL product specification level

PSL is referred to as the level of product specification. The product specification of the pipeline is divided into PSL1 and PSL2, there is a difference of only a single word, but the content of these two standards are completely different. The quality level of PSL2 is higher than that of PSL1, these two standards are not only different from the inspection requirements, but also the chemical composition and mechanical properties are different.

Why Need Post Weld Heat Treatment(PWHT)?

Due to the steel pipe transporting gas or liquid need to bear a certain pressure, internal stress produced in the cold rolling process must be eliminated. Welding process, because local overheating will cause the pipe deformation and shrinkage stress, so steel pipe return to heat treatment after welding to eliminate internal stress.

PWHT is based on the hardness of the steel, the thickness of the welding parts, structural rigidity, welding methods and conditions of use. General carbon steel welding performance is good, the welding can be without preheated and heat treatment. But for the high carbon content and high stiffness of the welding parts, it is required to preheat and heat treatment, such as the wall thickness of 30mm carbon steel pipe.

Method of PWHT

The method of PWHT is electric heating. The caterpillar electric heater and linear electric heater should be fixed on the parts which are needed to PWHT; they connect with the automatic controller through cable. And the thermocouple should be fixed on the parts needed to PWHT through the compensating conductor. It connects with the computer automatic controller. Then the controller will work automatically according to the process parameter that is being inputted into the controller.

General rules for PWHT

• On the stress corrosion of the weld, should be carried out post weld heat treatment.

• Prone to delayed crack in steel welding, it should be timely carried out heat treatment after welding. When the heat treatment is not timely, it should be heated to 200℃~300℃ immediately after welding, and the heat preservation and slow cooling, the heating range should be the same as the PWHT.

• After welding heat treatment and before the pressure test, appearance inspection and non-destructive testing should be carried out.

• PWHT qualified parts, should not engage in welding operations, otherwise it should be re-heat treatment.

• Welding inspector should be professional trained and welding heat treatment personnel should be in accordance with the norms and welding work instructions to handle heat treatment.

• When heat treatment is carried out, the temperature should be measured and recorded, the position and quantity of the temperature measuring point should be reasonable, and the temperature measuring instrument should be qualified and effective.