1 Foreword The Party Central Committee made a strategic decision for the development of the western region. The “West-East Gas Transmission†project, one of the key projects in the development of the western region, is about to start the “West-East Gas Transmission†project, which is to transport a large amount of natural gas from the Tarim Oilfield in Xinjiang to the steel pipeline. Shanghai is a major project that benefits the people of the east and the west. According to reports, the main pipeline of the West-East Gas Pipeline Project is 4,167 kilometers long and runs through 9 provinces, municipalities and autonomous regions. After the construction of the first phase of the project, the annual gas supply capacity of 12 billion cubic meters will be started in April 2001. At the end of 2003, the entire project will cover 1.75 million tons of steel and 5100 tons of welding consumables. The main pipeline investment will be 38.4 billion yuan. The investment in the main line and urban pipe network will exceed 100 billion yuan. The main pipe diameter is 1118mm. It is 8.4 MPa, including 1.37 million tons of spiral welded pipe, 16.4 mm wall thickness, 380,000 tons of straight welded pipe, and the wall thickness of straight welded pipe is 17. The material grade is medium plate X65 has good property and weldability. Reported that as the first line of "West-East Gas Transmission", Qinghai Yubei, Xining, Lanzhou, and Lanzhou natural gas pipeline project started construction on April 1, 2000. The project is expected to cost 2.5 billion yuan. It is 953 kilometers long and has an annual gas transmission capacity of 2 billion cubic meters. It is expected to be completed in October 2001. The main official road diameter is 660mm, the wall thickness is 3mm, the steel grade is X60, and the gas transmission pressure is 6.4MPa. Project management implements owner responsibility system and implements project construction in accordance with international practice The whole process management, engineering quality welding non-destructive testing system, 100% radiographic inspection according to the conventional inspection method, the oil and gas long-distance steel pipeline butt welds mainly use X-ray film photographic inspection, this method requires a lot of X-ray film, long detection period, large amount of labor, patch, filming, and washing process are complicated, and pipeline construction is mostly in the field, which brings more difficulties to filming and washing. In today's high-tech development, The implementation of the magnificent "West-to-East Gas Transmission" project should break the conventional use of advanced technology in accordance with the current technical level of non-destructive testing, and it is feasible to use X-ray digital real-time imaging detection technology in the "West-to-East Gas Pipeline" butt weld inspection. .
2 Basic requirements for butt weld inspection of natural gas long-distance pipelines According to the current standard, the construction and acceptance of natural gas long-distance pipelines shall be carried out according to the standard of “Construction and Acceptance Specifications for Long-distance Pipeline Line Engineeringâ€. SY4056-93 (Determination of radiographic quality classification of butt welds in oil and gas steel pipelines). When the working pressure is greater than or equal to 4 MPa, the quality of the weld is qualified according to the grade; when the working pressure is less than 4 MPa, the grade I is qualified. In the construction of a natural gas pipeline in foreign countries, the X-ray real-time imaging inspection method was used to detect the weld seam. (Note: “X-ray real-time detection†and “X-ray digital real-time imaging†in this paper are used to ensure the weld quality.笕 æ¤ æ¤ æ¤ å¬‰ 嬉 嬉 嬉 嬉 嬉 嬉 嬉 嬉 嬉 嬉 嬉 嬉 嬉 嬉 嬉 å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’– å’–Degree is not more than 0.25mm (equivalent to image resolution 1. With the development of non-destructive testing technology, X-ray digital real-time imaging detection technology can now be applied to the weld Non-destructive testing, for example, X-ray digital real-time imaging detection technology has been formally applied to the non-destructive testing of gas cylinder butt welds. China has issued GB17925-1999 national standard for X-ray real-time imaging inspection of butt welds of gas cylinders, which is X-ray digitalization. Real-time imaging technology provides a successful experience in the promotion and application of butt weld inspection in natural gas long-distance pipelines. 3X-ray digital real-time imaging detection technology can replace film photography. X-ray digital real-time imaging detection principle can be used with two (or imaging panels) Implicit X-ray detection signals are converted into visible analog images; analog images are input into a computer to convert analog words, and digital images are formed to provide various information about surface and internal defects of metal materials, using computer programs for digital images. Evaluate for non-destructive testing of metallic materials. When using microfocus imaging high-definition image enhancement technology, high-resolution digital acquisition technology and computerized digital image processing technology, and high-resolution image display technology, X-ray digital real-time imaging quality
4 X-ray digital real-time imaging detection scheme for long-distance pipeline steel butt welds According to the actual situation of oil and gas long-distance pipeline laying in the current and future period, the nominal outer diameter of steel pipe is usually 0323.9~ image intensifier, and the pole is on the track. By rotating N in equal parts, the image intensifier can receive X-ray detection signals in N divisions. To prevent damage to the image intensifier, the image intensifier should be kept at a certain distance from the weld.
According to the principle of geometric projection, the image detected by X-ray real-time imaging is magnified, and the magnification M is: image enlargement is not only caused by geometric projection, but also necessary to improve image quality. The image magnification depends on the performance of the device. Usually there is an optimal magnification: the focus size of the d-ray machine is measured by the test method, and the minimum defect size dmn detectable by the mm image is: D-one image intensifier input screen Diameter: for example: 6* image intensifier, input screen diameter D=150mm, image magnification M=M, = 4.1 For ring welds with a nominal outer diameter of 0, the circumferential center internal imaging method can be used, such as For the 100% inspection of the weld, in order to not miss the inspection, consider a 5mm overlap length on both sides of a test image, then an image is shown.
A small focus circumferential X-ray flaw detector is placed over the pipe crawler, the crawler crawls within the pipe, and the isotope tracking monitor is used to focus the circumferential X-ray machine on the girth weld.
The effective detection length Lff is: Leff-125-5-5=115mm, for example: the butt joint weld of the outer diameter 0660mm pipe (the weld height is 2mm), the circumferential length is 2080mm, then one ring weld is required (2) by two Semi-circular mechanical rotating guide rail, fixed to the ring to detect N images: one side of the weld bead, there is a pole on the rail, the pole can be rotated around the rail by N equal parts, 13 poles are installed, one cantilever is installed on the suspension Her enterprise House. 1118mm pipe butt joint weld (weld height 2mm), the circumference length is 3518mm, then a ring weld needs to detect N images: L1L2 is determined according to the process parameters. Image magnification M, the minimum defect size that can be detected by the optimal magnification - the image detection length L3 and the effective detection length Lf of an image are as follows: N is the design parameter of the mechanical rotation orbit rotation.
Since the ray digital real-time imaging detection technology uses computer image processing technology, the image processing speed is fast. Usually, the time required for "acquiring and processing" one image is 4s, and the time for mechanical rotation orbit to rotate an aliquot (115mm) is about 6s. The total time required for detecting a 660 ring weld is 10s: for a X-ray machine with good cooling performance, a 0 1118mm ring weld can be completed in 6min-time exposure; for general performance X-ray flaw detector (exposure time) 5 minutes, 1:1 cooling method), can be completed in two exposures, the loading and unloading movement assist time of the mechanical rotating track is about 10 minutes, and the entire welding seam on-site inspection time can be completed in about 20 minutes, which is more than the film photography method. The speed greatly improves the flaw detection of long-distance pipeline welds, usually equipped with flaw detection engineering vehicles, computers and consoles are assembled in the engineering vehicles, easy to operate, radiation protection is guaranteed, mobile fast X-ray high-voltage cable and image intensifier cable The wire can be lengthened appropriately, so that the radiation protection is more suitable for the butt joint weld of the 502<8.7X60 steel pipe (the weld height is 2mm), the circumference Degree 1590mm, the time required for a ring weld to detect 502mm ring welds of N images is 140s, together with the auxiliary time, about 15~5 basic configuration of equipment according to the characteristics of field construction of natural gas long-distance pipeline, x-ray digital real-time Imaging inspection equipment should be as light and durable as possible.
all.
The focus of the 5.1 X-ray machine X-ray machine is placed on the center of the cross-section of the steel tube. The thickness ratio of the weld through-transparent is K=1.0, which is beneficial to improve the uniformity of the image quality. Due to the circumferential exposure technique, the circumferential ray points to the sky or the pointing tube. In the soil layer of the ditch, most of the excess rays are absorbed by the air or soil layer to reduce the influence of scattered rays. The image intensifier housing should be well grounded. If necessary, the outer shell of the image intensifier can be wrapped with a thin lead plate. The shielding of the scattered line is 甩 4.2 nominal outer diameter 0323. The girth weld of the 630mm pipe can be double-walled single-image imaging method, as shown.
The double-wall single-image imaging method does not require a crawler. The inspection tooling is a mechanical rotating guide rail composed of two semi-circles, which is fixed on one side of the edge of the ring weld. The guide rail is provided with two poles, and a fixed rod image is arranged 180* symmetrically. The intensifier, a pole fixed the X-ray head; the entire rail can be rotated by N in 360* around the centerline of the steel tube. There are several options for image X-ray machines, but regardless of the choice, the focus size should be less than or equal to 0.8 <0.8mm, and the X-ray tube is preferably made of cermet tube (1 ordinary circumferential portable X-ray machine. SF6 gas insulation, Forced cooling of the fan. It is best to use variable frequency power supply, the frequency is increased from 120 to 300 Hz, and the rectified wave type is approximate square wave, which is beneficial to the X-ray stable radiation without the cable X-ray machine with its own power supply. The machine is integrated with the pipe crawler and the power comes from the battery.
According to reports, this kind of X-ray machine can walk 2000m on one charge, weld 10 (% of flaw detection, walking distance is not less than 1000mm, using isotope tracker to control the positioning of portable DC constant pressure small focus X-ray machine outside the tube. High pressure occurs Separated from the X-ray tube, connected by high-voltage cable, sealed by circulating water, can work for a long time, the X-ray tube head is lighter, the intensifier and X maintain a certain distance from the outer wall of the steel pipe 1 but the high-voltage cable moves Trouble http:// 5.2 Crawler When using the circumferential center internal imaging method, the crawler is needed. The crawler is mainly used to carry the X-ray machine to walk, can crawl 15* slope, and the positioning is accurate. The positioning error is ±10mm. The crawler has a more mature technology and a more complete variety of image strength devices for the user to select 5.3 image intensifier 8LP/mm. The input screen diameter is 150mm. (The input screen has a large diameter, which is bulky, which is not conducive to movement, and the resolution is low; the input screen has a small diameter, although the resolution is large, but the effective length of the weld is small, which is unfavorable to improve work efficiency.) 5.4 Image Intensifier The rotating track is designed and manufactured according to the outer diameter of the steel pipe. The image strength device can be rotated 360° in the orbit according to the distance of N. The deviation of the stroke of each rotation should be controlled at ±5. The camera adopts the conventional CCD camera. The image is output as an analog signal. After being captured by the image acquisition card and subjected to A/D conversion, the image is processed into the computer for CCD digital camera. The acquisition resolution is not less than 768<576 pixels, for example, 1280 (1024 pixel digital). The camera outputs digital signals, which can be directly input into the computer for image processing. The CCD camera is a charge coupler with small volume and long working life. The CCD camera is placed behind the image output screen and integrated with the image strength device. .
5.6 computer according to the current computer performance price level, as far as possible using the higher file configuration: 333MCPU, 128M memory, 10G hard drive, 43cm (17 inches) 0.25 image line progressive color display, refresh rate 85Hz, and with floppy drive CD-ROM and CD-ROM The recorder computer is used to collect detection information, perform image processing, and perform auxiliary evaluation on the detected image. Through computer image processing, the inspection result in the weld seam can be seen in real time. The detection image is recorded on the optical disc and can be stored for a long time. The computer is placed in the inspection vehicle. The inspectors operate in the car. Usually two computers are configured in the work car, one for image acquisition and processing, and the other for image evaluation. Two computers can be networked in a peer-to-peer manner.
The line connects the laptop to the in-car computer; or after the on-site inspection is completed, the laptop is returned to the car and connected to the in-vehicle computer for image processing and image evaluation. The operating platform of the computer operating system is 5.7. Combine the actual situation of butt weld flaw detection in long-distance pipelines, and develop image acquisition image processing like evaluation applications, such as "SSCX2000 real-time imaging inspection program"
5.8 Equipment System Comprehensive Performance Evaluation The comprehensive performance of the equipment system has a great impact on image quality.
The comprehensive performance index of the equipment system can be expressed by the system resolution. It actually reflects the inherent unsharpness (Us) of the system according to the GB17925 standard. The system resolution should be greater than or equal to 1. 4LP/mm system resolution and equipment subsystems. Performance related. According to the current performance level of the equipment, the resolution of the X-ray digital real-time imaging detection system can reach 1. The image quality provides the necessary equipment guarantee.
6 Basic method The X-ray machine is placed on the crawler into the tube, and the crawler is manipulated outside the tube to focus the X-ray machine on the weld.
Fix the image strength rotation track on the edge of the weld, adjust the/2 distance according to the magnification set by the process, and the image strength device is aligned with the center of the weld.
A lead code and image quality meter and a resolution test card are attached to the surface of the weld.
After the flaw detector collects an image in the engineering vehicle operating the computer and the flaw detector controller and the rotating guide rail, the image strength device rotates 1/N, and then captures an image statically until the N image is collected and shuts down. Move to the next weld and repeat the above procedure.
Perform computer-aided evaluation of the detected image, print the flaw detection report, burn the disc, and save the test result.
7 Standards It is reported that the State Bureau of Quality and Technical Supervision is organizing relevant departments to formulate the national standard of “Steel butt weld X-ray digital real-time imaging inspection†equivalent to GB3323. Before this, the X-ray digital real-time imaging detection of the butt weld of natural gas long-distance pipeline The method can refer to relevant standards, formulate industry or enterprise standards, and use it temporarily after approval. If the field work environment is poor, the engineering vehicle is difficult to approach the inspection location. The image can be collected by a portable computer, and the image quality evaluation by cable Msg is served. .http:// degree, image resolution three elements for evaluation.
The 93 standard is equivalent to the 93 standard. The blackness control range of the film is 1.2~3.5, and the image gray level is controlled at 80~230. (Note: the image grayscale variation range is defined as 8bit, ie 256 levels.) The image resolution is in accordance with the transillumination thickness. For the third gear: transillumination thickness 25mm, image resolution 25mm, image resolution> according to the current equipment configuration and technical level, the above quality indicators can be achieved 9 feasibility analysis 9.1 technical feasible China began research in the late 1980s X-ray digital real-time imaging detection technology has achieved fruitful results. The official release of the GB17925-1999 standard marks that X-ray digital real-time imaging detection technology can be applied to the non-destructive testing of steel welds. This technology is used in the inspection of steel welds. The successful experience provides a useful reference for the application of butt weld inspection in natural gas long-distance pipelines. Therefore, it can be said that the application of this technology in the weld flaw detection of natural gas long-distance pipeline is feasible. 9.2 Benefit Analysis 9.2.1-Secondary Investment in accordance with the performance and price level of current equipment and technology (the technology mentioned here is mainly knowledge value), a set of X-ray digital real-time Due to different equipment configuration choices, the price will have a larger expansion and contraction compared with the original film photographic inspection method, although the one-time investment is large, but the technology is mature, the investment risk is small, the return rate is high. 9.2.2 Direct economic benefit due to X-ray Digital real-time imaging detection technology can replace the original film photographic inspection method. The cost of film saving is very large. The width of the image is 1/3 of the full screen, and the capacity occupied by one image is 1280 (1024 (1/3=437kB). ), the test image is saved on a CD-R disc with a capacity of 650M, then one disc can hold 1440 images (6500.437=1487 frames). If the image is detected in an image, the weld seam detection length is calculated as 115mm, and the disc storage capacity is calculated. Equivalent to 480 (1440H3 = 480) photographic film. According to the current price level, a premium CD is priced at 50 yuan, and the test image is saved in duplicate, the cost of the CD is 100 yuan; The direct cost of photographic film is calculated at 20 yuan, and the direct cost of X-ray digital real-time imaging detection is only 1% [100/(480<20) = 1%] of the direct cost of film photography. The economic benefit is very impressive. The digital real-time imaging test is 1km of 1118mm pipeline. It takes 4.5~6 sheets (90<3 1440<2=4.5) to save the image. The cost is only 300 yuan. A weld seam needs to take 12 negatives. If the 1km long pipe is compared, the 1km pipeline inspection cost can save 20,000 yuan (21600-300=21300 yuan). If an engineering company contracts 1001 to welcome the 01118mm pipeline construction task, adopt X-ray digital real-time imaging detection technology can save 2 million yuan in testing costs, which means that only one cost can be recovered.
9.23 Indirect effect X-ray digital real-time imaging detection technology to detect a 01118mm pipe girth weld, exposure time of 6min, plus a variety of auxiliary time, according to a conservative estimate of up to 60min can complete a weld flaw detection task, and instantly Seeing the test results of the internal quality of the weld, the detection speed is greatly improved, which is of great significance to ensure the on-time tools of the entire project.
X-ray digital real-time imaging detection can replace the film photographic detection method, so it can save the cumbersome process of patching, filming, washing, etc. It is of great significance for field construction, especially in the deserted Gobi area where water is scarce. X-ray digital real-time imaging detection technology is feasible in the application of natural gas long-distance pipeline weld flaw detection.
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