Ten special problems to be solved in the Sichuan Chongqing region by the constant pressure belt plugging technique

(1) simulation experiment. In the block before construction, hole plugging experiment according to the situation, the process parameters obtain current, temperature and time of three links and short time of welding, and the evalsuation factors and the effects of the closure conditions.

(2) special shaped three pass and short joint anticorrosion after sealing. In the past, the special three links and short sections of the sealing block were treated by the traditional asphalt anticorrosion treatment. The anticorrosion effect was poor, and it was not conducive to cathodic protection. The author recommended the use of STOPAQ company's excellent adhesion, anti - cathodic protection, stripping characteristics.

(3) welding procedure qualification. There are many kinds of pipeline material in Sichuan and Chongqing, and the main welding work in non-stop pressure transmission and sealing is bypass three pass, plug three pass and balance short joint, and the outer joint of lower capsule joint and main line. Because the three pass and the short joint are made by the special manufacturer, the material is not completely consistent with the material of the main line, and the welding procedure qualification must be done first.

(4) the basic low hydrogen electrode is used as manual arc welding in the pipeline welding of Sichuan and Chongqing, and the CHE427 or CHE507 is chosen according to the material of the pipeline, so that the performance of the weld metal meets the requirement of use. Because of the complicated shape of the weld at the hole, manual arc welding can only be used

Yuan Pingfan, born in 1965, high engineer; Mechanical Engineering Department of Southwest Petroleum Institute in 1988 graduated from the original, served as the national oil station deputy stationmaster, Chengdu time flow of natural gas station director, China Southwest Oil & gas field pipeline maintenance center China of Southwest Oil and gas company gas management office deputy chief engineer. Address: (610215) Huayang District, Chengdu, Sichuan. Tel: (028) 856013031380806118. E-mail:pingfanyuan@126.com

The negative pole is selected for the power supply, and the positive pole is selected for the second times welding power source. The girth of the girth welds shall be no more than 10% of the arm thickness and not greater than 2mm. The quality of welded joints shall meet the following requirements: 1. No cracks, no fusion, air holes, slag inclusion and spatter exist; and the diagonal welds shall be checked by the JB4730 standard for nondestructive testing of welded joints of pipes.

The process parameters of pressure welding are shown in table 1.

Table 1 pressure welding parameter table (experimental data of pipeline network in Sichuan and Chongqing area)

Level electrode diameter, welding current, electric voltage, welding speed, interlayer temperature

(mm) (A) (V) (cm/mim) (C);

The first layer is Phi 2.5 70~85 22~24 7~8

Second layers Phi 3.2 95~115 22~26 7~8 80~100

Third layers Phi 3.2 95~115 25~26 7~8 80~100

(5) plugging point. Should try to choose in the horizontal pipe section. The opening shall avoid the spiral weld and girth weld of the pipe. If it can not be avoided, the opening of the welding parts should be properly polished. The center hole shall not be placed on the weld seam. The pipe ellipticity and wall thickness error of the sealing part shall not exceed 1% of the pipe outer diameter.

(6) requirements for operation pits under Sichuan and Chongqing geographical conditions. According to the field experiment, the length of operation pit is generally not less than 12D (pipe diameter), and the width is not less than 6D. The area of the machine and the vehicles on both sides of the operation pit shall be no less than 1500m2. The depth of operation pit is not less than 0.6m, the slope of slope is 1:0.6, there are no other pipelines and optical cables in the pit, and there is no line in the 8m height above the ground.

(7) the velocity limitation in the pipe. Through theoretical calculation and simulation experiments, the gas flow rate in the pipeline in the Sichuan Chongqing region should be no more than 10m/s when sealing and welding pipelines. The flow velocity of liquid medium shall not be greater than 2.5m/s. When the gas pipeline is blocked by pressure, the medium flow rate shall be no more than 5m/s.

(8) in addition to the temporary bypass and construction of pipelines must be put into operation before nitrogen injection to exclude air, each household hole plugging device, should be the first to exclude air equipment to vent the nitrogen injection, the nitrogen content is more than 98% qualified. Take the phi 720mm pipeline as an example, the nitrogen injection rate is about 2m3 before each opening and plugging.

(9) the non-stop transmission with imported equipment and accessories plugging technique in large proportion, considering its high price, long supply cycle, and the cutting tool, O type sealing ring is used in the British standard, sometimes do not match with the domestic diameter; operation involving three Tongse handle consumables consumption large, similar equipment in Sichuan and Chongqing area has been gradually switch to domestic Shenyang, Shenyang Yada Liaohai machinery factory machinery factory, Xinyu Feihu pipeline equipment company supplies.

(10) programme templates and safety plans. 3 sets of standard schemes for plugging with pressure and 4 sets of standards for plugging operation of Sichuan Chongqing pipeline network have been formed, and they have been tested in the second plugging project.