Rapid construction method of chemical small diameter pipelines

In view of the generally small diameter of chemical test equipment piping, the construction process of chemical small diameter piping is combined with the thesis case, and the construction preparation, prefabrication and field assembly of chemical small diameter piping, as well as the construction methods and advantages and disadvantages of each stage are discussed, which provide reference for the construction of similar small diameter piping.

0. Introduction

With the upgrading and technological transformation of large chemical plants in China, various kinds of chemical test installations are emerging, which are usually built next to existing installations. Take a chemical test project of Sinopec Sichuan vinylon plant pilot plant as an example, the plant was upgraded by using the structure of the original test plant. The effective use of the site area of 236m², in the test facility, chemical pipeline diameter in the quasi 57 × 3.5 and above the length of 410m, while the specifications in the quasi 57 × 3.5 below the length of the pipeline 885m, the number of small diameter pipeline accounted for about 68% of the total number of pipelines in the entire device. In the main parts of the pipeline welding: elbow (331), tee (157), reducer (19), flange (391 pieces), instrument root original (35 pieces), from which we can see that the number of elbows accounted for 35% of the total number of welded parts, the number of flanges accounted for 42% of the total number of welded parts, the welding work of these two parts of the components of the main workload of on-site welding.
In the construction of pipeline systems generally use the flange connection to connect the two parts of the pipeline components, due to a variety of valves are used to connect the flange, therefore, the way the pipeline welding flange can not save the process; pipe elbow connection is generally available small diameter pipe plasticity characteristics, the use of pipe bending instead of finished elbow, at the same time, to reduce the welding process. In the pipeline construction, if you can use a combination of hot simmer bend, bender pressure bend, special mold pre-bending advantages, and unified pipeline prefabricated, will be able to change a large number of pipe welding process to centralized bending plus a small amount of welding construction; at the same time, advance three-dimensional conception to consider a good pipeline and the rest of the pipe system block assembly sequence, you can give full play to the advantages of small diameter pipeline construction, so that the chemical test equipment small diameter pipeline construction The workload and construction cost of small and medium diameter pipeline construction in the chemical test facility are greatly reduced, and the construction efficiency is further improved.

1. Construction method

The construction steps of small diameter pipeline are:

• (1) Combine with the design drawings and equipment site installation conditions for overall consideration, draw a single line drawing of each pipeline, and on the drawing for the block segment preparation.
• (2) Organize relevant professionals to prefabricate and assemble into pipe system blocks.
• (3) Assemble each pipe system block as a whole according to the overall layout.

1.1 Construction preparation

In the construction process, should give full play to the advantages of small diameter pipeline construction, to avoid or reduce the disadvantages of small diameter pipeline construction, the overall should consider the following three points:

• (1) Draw a single line diagram. General pipeline design will not provide a single line of small diameter pipeline construction, but by the construction unit technicians to determine the direction of the pipeline according to the design of the general plan, combined with PID diagrams to determine the composition of other components on the pipeline, while verifying the pipeline material table to verify whether there are missing components on the pipeline, and full communication with the design and process operators, in a full rationalization of each pipeline direction and installation After fully rationalizing the direction of each pipeline and the installation situation, a single line diagram of the pipeline is drawn.
• (2) Consider the location of the pipeline construction site. Check whether the site pipeline installation location conditions to meet the construction requirements, to ensure that the pre-installation part of the subsequent construction does not cause any impact, integrated valve block installation and operation and easy to use the operation of the regulating valve on the pipeline, these should be combined with the actual situation at the site, reasonable layout, set aside a good pipeline fixed weld, fully consider the location of the valve block, to avoid repeated demolition, installation of the valve block and the use of the valve block inconvenience, at the same time, to reduce At the same time, reduce the work at height and unfavorable position.
• (3) Pipe system blocking and pipeline preparation. After overall analysis and consideration, the whole pipeline was divided into several pipeline blocks by combining the construction drawings and site conditions, and the materials and quantity of each pipeline block were counted, and the personnel were organized to prepare materials and prefabricate the pipeline blocks.

1.2 Prefabrication of pipeline

(1) The simmering bend of the pipe. The number of small diameter pipes can be bent is very large, must be an experienced riveter specifically focused on bending work, and choose a reasonable way to make bends for prefabricated, can save time in the construction of the back.
Hot bending, is the direct heating of the body of the pipe through the oxyacetylene flame, and then force the pipe to push the bend to a certain angle, so that the bend out of the bend radius is generally larger, the use of a wider space in the field location, this method of production is highly efficient. The focus of the heat bending method: First, according to the formula for calculating the arc length of the bend, the part of the pipe to be bent to draw the arc length of the bend and the arc length of the midpoint; then, the pipe is heated, the heating temperature should be controlled in (carbon steel) 750 ℃ -1050 ℃, in the range of pipe bending heating and thrust on the pipe to be uniform, so that the curve of the prefabricated elbow will be uniform.
The focus of the pre-bending construction method: the pipe is bent close to the bending die, anti-deformation rollers restrict the pipe around the center of the bending die arc around the circle, the bend of the pipe = bending die rotation angle + 20 ° (20 ° for the empirical value of carbon steel, the reason: the rebound of the pipe and the impact of the gap between the two wheels). This group of molds designed to anti-deformation roller and bending die with the use, as shown in Figure 1, the roller groove using a double arc R₂, R₃ egg-shaped, its depth H is greater than the radius of the pipe R₁. bending die using a semicircle, its depth than the pipe radius R₁ small 1 mm, R₁, R₂, R₃ size and the relative bending radius and pipe outside diameter D (as shown in Table 1 R_X = R/D, R is the center layer of the pipe bending radius, D is the outer diameter of the pipe), so the pipe ellipticity can be reduced, and in an ideal state, the ellipticity of the elbow part can be reduced to zero. In the process of construction must be noted that after a period of time in the use of anti-deformation roller will wear, anti-deformation groove into a circular groove must be replaced, otherwise the pre-bend will be very deflated, the amount of thinning of the outer layer of the pipe wall increased dramatically. This method is applicable to the diameter of the pipe is about 25, the wall thickness is thin, simple tooling, low cost.

Figure.1 Pre-bending processing grinding tools
Table.1 Bending radius of bends

Relative bending radius RX	R1	R2	R3	H
1.5–2	0.5D	0.95D	0.37D	0.56D
2–3.5	0.5D	1.0D	0.4D	0.545D
≥ 3.5	0.5D	—	0.5D	0.5D

Pressure bending construction method focus: has been processed elbow must be bent with the three fixed points of the press bending tooling in a plane or vertical plane, in order to ensure that the production of elbows and pipeline components horizontal and vertical.
(2) The assembly of prefabricated pipeline valve group. According to the construction drawings, a group of personnel is specially arranged for the construction of the valve group, due to the light weight and small volume of small pipes and valve groups, the pipe prefabricated parts and flanges can be welded first, and then assembled into blocks with valves, and according to the pipeline number to the pipe system block number, transferred to the next group of personnel to carry to the site assembly.
1.3 On-site assembly
The prefabricated pipe system blocks will be assembled into a piping system, to comply with the following principles:

• (1) First to ensure that the material pipeline and large diameter pipe assembly, and then the utility pipeline and small diameter pipe assembly;
• (2) Separate finished elbow installed in a narrow construction location, prefabricated elbow installed in the unobstructed space, elbow and elbow reasonable distribution;
• (3) Small pipes must be unified production of brackets, such as the following two cases. The first case, the arrangement of the pipe row, the bottom of the riser row of fixed brackets, and about 2 m interval in the vertical direction of the pipe row were installed sliding bracket, so that the pipeline to maintain a relative distance, mutual constraints, to reduce jitter; the second case of the valve or pipeline components in the air, due to the small diameter pipe rigidity is poor, must make special bracket, and U-shaped card to do circumferential fixed.
• (4) The original instrumentation on the pipeline must be considered in advance of the location, without being blocked by other pipes.

2. Case study of small diameter pipeline construction

2.1 Drawing single line diagram and blocking

As the project is adjacent to the original device construction, the pipeline layout on the plan during construction is often blocked by other pipelines on the site of the old device, resulting in the installed ones to be removed; in the construction, due to the lack of overall consideration, resulting in inconvenience in the operation of valves on the pipe system, the installation of brackets on the pipeline is not standardized, etc., making the later acceptance of the rectification problems are generally more. Before construction, a single line diagram should be drawn for each pipeline system and divided into blocks according to the shape size of the pipeline system and the distribution of various parts on the pipeline (as shown in Figure 2), and the figure shows a pipeline system block in the single line diagram.

2.2 Prefabrication of small diameter pipes

In the construction of each processing method has advantages and disadvantages, the finished welded elbow and bending (such as Figure 2, 3 shown in the cloud line part) to compare the following.

Figure.2 Method 1 welding prefabricated pipeline
The characteristics of welding: advantages, welding a wide range of practical, centralized construction to improve the quality of welding; disadvantages, complex processes, high costs, easy to leak, easy to become smaller pipe diameter.
(Hydraulic bender) pressure bending characteristics: advantages, no work platform, construction is more flexible, processing parts than the hot bend specification; disadvantages, the outer circular surface of the pipe wall is easy to thin, easy to deflate, low efficiency, the same pipeline processing multiple bends, the relative size is not very accurate, and the size between the two bends must be larger than the size of the tooling opening.
(Bending die) pre-bending characteristics: advantages, good quality, high efficiency, continuous processing of multiple bends in the same plane; disadvantages, more laborious, anti-deformation rollers easy to wear, tooling on the processing of the larger constraints.
Hot simmering bending characteristics: advantages, high processing efficiency, no mold bondage; disadvantages, heating temperature is not good control, easy to cause the pipe bending wave drum type, the bending radius is not standardized.
Usually in the construction of several methods are used, but generally use one or two processing methods combined with the processing of the pipe, without giving full play to the characteristics of pre-bending, pressure bending, hot simmering bending and welding. According to the example of welded elbows and bending combined processing methods, from both the process and cost analysis.
Method 1 welding prefabricated pipeline (as shown in Figure 2), the process: (1) cutting preparation (5 sections); (2) beveling (10); (3) weld assembly (9); (4) weld detection (according to the medium to determine the number of weld detection).
Method 2 multiple methods combined with prefabricated pipeline (shown in Figure 3), the process: (1) cutting and preparation (1 section); (2) pipe mounted on the tooling platform continuous pre-bending (3 times); (3) pressure bending (1 time); (4) weld port assembly tee (1).
Analysis from the process: both methods are four processes, but it is clear that the first method 1 (2) (3) process more repetitive labor, more time-consuming; and method 1 (4) process cycle is longer. Method 2 of the three pre-bending is continuous, so that the pipe in the same plane bending three times, and then the pipe between the first and second pre-bending straight pipe section fixed in the hydraulic pipe bender, so that the bending plane rotated 90 °, a pressure bending, that is, the completion of the workpiece processing.
Cost analysis: method 1 on the use of argon gas, welding wire more, higher detection costs; method 2 mainly through human processing. It can be seen that method 2 combines the advantages of the three processing methods to improve efficiency.

Figure.3 Method 2 multiple methods combined with prefabricated pipeline

2.3 Field assembly of small diameter pipe manifold and pipe system block

Due to the small size, light weight, easy handling and convenient installation of pipes and valve sets, some pipes and valve sets can be assembled first to form pipe system blocks. Each pipe system block will be assembled on site according to the sequence of the single line diagram, and the fixed welding ports (as shown in diagram 4, G10# and G27#) will be left on the ground as much as possible to reduce overhead work. According to engineering experience, this installation idea is more efficient than the traditional prefabricated section installation section construction method by about 30% or more, and the workload of prefabricated pipe system reaches 80% of the entire pipe system workload.

Figure.4 Pipeline valve group

3. Conclusion

The installation space of this project is narrow, the small diameter pipeline crosses densely and there is no design single line diagram support, in the actual construction according to the construction characteristics and environment reasonable choice of construction methods, make full use of the characteristics of small diameter pipeline construction, to achieve the project fast construction, in the project construction overall consideration of the construction sequence, not only to save construction costs and improve efficiency, the success of this project can be small diameter pipeline construction project The success of this project can provide a good reference for small diameter pipeline construction projects.
Author: Gan Wubo