CN105806412A - Annular detector for intelligent submarine pipeline soil mass axial actions - Google Patents

Abstract

An intelligent annular detector for the axial action of submarine pipeline soil, which consists of an upper support made of aluminum alloy, an annular shear surface, four fixing rods, a loading arm, four pore pressure sensors and four lead wires of the pore pressure sensors. Four fixing holes and four sensor lead holes are evenly distributed on the upper support; the upper support and the annular shear surface are fixed by vertical and evenly distributed fixing rods, one end of which is vertically fixed to the center of the upper support, and the other end is connected to the seabed detection On the control execution system of the equipment; the pore pressure sensor is fixed in the sensor hole on the annular shear surface; the vertical pore pressure sensor leads are connected to the pore pressure sensor and pass through the sensor lead holes of the upper support to be respectively fixed to the loading arm for connection to the data acquisition system. The invention has the advantages that: the detector can be effectively applied to the field survey in the early stage of the project, provide strong technical support for the design project of the submarine pipeline, and greatly save the project cost under the premise of ensuring the safety and reliability of the project.

Description

An intelligent annular detector for the axial action of submarine pipeline soil

technical field

The invention relates to the field of on-site investigation and monitoring of deep-sea rock and soil, in particular to an intelligent circular detector for the axial action of seabed pipeline soil.

Background technique

As submarine pipelines gradually enter the deep sea and even ultra-deep sea, the traditional solution of digging trenches and filling them to completely limit the buckling and movement of pipelines is difficult to implement in deep seas. Accordingly, the design concept of lateral buckling (lateral buckling) submarine pipelines was proposed , Abandoning the traditional method of setting the stress (or moment) level to limit the buckling, and using the pre-designed lateral buckling to safely and effectively release the thermal expansion stress of the high-temperature and high-pressure sea pipe by means of controlling the strain.

The design scheme of the lateral buckling submarine pipeline makes the construction convenient and the cost is greatly reduced. However, during the operation process, the intermittent start-up and shutdown operations of the submarine pipeline will cause the axial displacement of the pipeline to produce a ratchet effect, which is usually called the ratchet phenomenon (pipelinewalking). ). With the intensification of the ratchet effect, the overall axial displacement of the pipeline will be relatively large, which may directly lead to stress overload damage of the spool between the pipelines and the terminal equipment. In addition, because the predetermined lateral buckling divides the entire pipe into multiple shorter sub-pipe sections, on the one hand, as the axial displacement of the entire sub-pipeline develops, the bending strain of adjacent lateral buckling is overcompensated by it ( Excessive feed-in) may cause local buckling damage. On the other hand, the cyclical characteristics of expansion and contraction of the sub-pipeline segment during operation may cause fatigue damage to the pipeline itself.

Obviously, these potential engineering hidden dangers (or engineering accidents that have occurred) are closely related to the development degree of the ratchet phenomenon. How to effectively control the axial movement of the sea pipe without excessively increasing the engineering cost has become a problem. Unavoidable problems in engineering. Usually, when no measures are taken to restrict the axial movement of the submarine pipeline, the degree of ratchet phenomenon is limited by the critical frictional resistance in the axial direction of the pipeline. Therefore, its accurate evaluation directly determines the design and construction cost of the relevant inhibition of the axial movement of the pipeline (such as the size and number of bucket shallow foundations that define piping). In the current design scheme, a set of upper and lower limit values of the pipe-soil friction coefficient is often given to approximately consider the influence of the axial action of the pipe-soil, which may result in unacceptable axial movement or Design specifications are too conservative. The fundamental reason is that the axial friction design parameters of submarine pipelines have regional and time-domain variability. Specifically, regional variability is due to the obvious inhomogeneity of the soil in different geographical locations where the pipeline is laid, and the variability in the time domain. The characteristic is that the laying process of the pipeline (pipeline settlement and subsequent consolidation) and the operation process (intermittent reciprocating motion accompanied by consolidation) will cause changes in the axial friction of the pipeline.

In view of this, it is necessary to carry out relevant geotechnical site investigation and testing in the early stage of submarine pipeline design. Usually reliable on-site detection can provide detailed soil texture structure and related engineering design parameters to ensure the feasibility, safety and economy of the entire project. With the development and progress of seabed geotechnical survey technology, a series of seabed geotechnical survey equipment has emerged, and is dedicated to improving the accuracy and reliability of important engineering parameters, so as to effectively serve the entire process of submarine pipeline design, construction and operation. process. For example, Cone Penetration Testing (CPT) is widely used to detect engineering indicators such as soil classification, density and friction angle of seabed sand; T-shaped strip (Tbar) penetration detection It is mostly used to detect the undrained shear strength of seabed clay; and in order to effectively reflect the consolidation characteristics of seabed soil, the method of pore pressure static penetration testing (PiezoconePenetrationTesting-PCPT) is adopted. However, due to the complexity of the design of submarine pipelines, the commonly used relevant design parameters such as the above-mentioned survey equipment cannot effectively take into account the influence of the axial movement of submarine pipelines. Buried structures are more related to the mechanical properties of the shallow (or surface) soil on the seabed.

Contents of the invention

The purpose of the present invention is to analyze above-mentioned technology, provide a kind of annular detector of intelligent submarine pipeline soil axial action, this detection equipment, reveal the thermal ratchet effect of submarine pipeline, survey the engineering design index of shallow layer soil of seabed: undrained Shear strength index (clay) and pipeline initial buried depth index, pipeline consolidation settlement index, pipeline axial shear characteristic index and consolidation hardening index of pipeline axial friction resistance, so as to improve the on-site investigation and monitoring of marine rock and soil The equipment provides more reliable engineering parameters for the design of submarine pipelines and optimizes the traditional design scheme of submarine pipelines.

Technical scheme of the present invention:

An intelligent annular detector for the axial action of submarine pipeline soil, which is composed of an upper support made of aluminum alloy, an annular shear surface, four fixing rods, a loading arm, four pore pressure sensors and four lead wires of the pore pressure sensors. The diameter of the upper support is 500mm and the thickness is 15mm. The upper support is evenly distributed with four fixing holes and four sensor lead holes. The diameter of the center circle of the eight holes is 400mm; the annular shearing surface is a solid structure, and its The bottom surface is a spherical surface with a diameter of 200mm, and the upper surface is a plane with an outer diameter of 500mm and an inner diameter of 300mm; four fixed holes and four sensor holes are evenly spaced on the annular shear surface, and the diameter of the center circle of the eight holes is is 400mm; the upper support and the annular shear surface are fixed by four vertical and evenly distributed fixed rods, the diameter of which is 150mm and the height is 200mm; the diameter of the loading arm is 25mm and the height is 500mm, one end of which is connected to the upper support The center is fixed vertically, and the other end is connected to the control execution system of the seabed detection equipment; the four pore pressure sensors are fixed in the four sensor holes on the annular shear surface; the four vertical pore pressure sensor leads are connected to the four pore pressure sensors And pass through the four sensor lead holes of the upper support to be respectively fixed with the loading arm so as to be connected to the data acquisition system.

The beneficial effects of the present invention are:

The detector can be effectively applied to the field survey in the early stage of the project, so as to provide more reliable and accurate design parameters for the subsequent design of the submarine pipeline. More importantly, a large amount of valuable field survey data can not only provide strong technical support for new submarine pipeline design projects in the future, but also provide the necessary guarantee for further cost savings and optimization of submarine pipeline design schemes. Because the use of this equipment can effectively collect a complete set of real experimental indicators of the axial action of deep-sea pipes and soils (the initial settlement of the main oil (or natural gas) pipeline section during the pipeline laying and installation process and the undrained shear strength of the soil and Stiffness index, consolidation settlement during installation and commissioning, pipeline axial shear stiffness during normal operation, and consolidation hardening index of critical axial friction resistance, etc.), which provide a great resource for establishing a scientific and reliable numerical simulation model. Value database, and the use of economical, efficient and reasonable numerical model methods in the design of submarine pipelines with similar submarine working conditions can undoubtedly greatly save engineering costs on the premise of ensuring engineering safety and reliability. blank.

Description of drawings

Figure 1 is a schematic diagram of the three-dimensional structure of the ring detector.

Figure 2 is a schematic diagram of the top view structure of the ring detector.

Figure 3 is a schematic diagram of the structure of the ring detector viewed from above.

Figure 4 is a schematic diagram of the side view structure of the ring detector.

In the figure: 1. Loading arm; 2. Pore pressure sensor lead wire; 3. Upper support; 4. Fixing rod; 5. Pore pressure sensor; 6. Annular shear surface.

detailed description

Example:

An intelligent annular detector for the axial action of submarine pipeline soil, as shown in Figure 1-4, consists of an upper support member 3 made of aluminum alloy, an annular shear surface 6, four fixed rods 4, a loading arm 1, and four A pore pressure sensor 5 and four pore pressure sensor lead wires 2 are composed. The diameter of the upper support 3 is 500 mm and the thickness is 15 mm. The upper support is evenly spaced with four fixing holes 4 and four sensor lead holes. The circumference of the eight holes is The diameter of the central circle is 400mm; the annular shearing surface 6 is a solid structure, the bottom surface of which is a spherical surface with a diameter of 200mm, the upper surface is a plane, the outer diameter of the plane is 500mm, and the inner diameter is 300mm; the annular shearing surface 6 is evenly distributed at four intervals There are three fixing holes and four sensor holes, and the diameter of the center circle of the eight holes is 400mm; the upper support member 3 and the annular shearing surface 6 are fixed by four vertical and evenly distributed fixing rods 4, and the diameter of the fixing rods 4 is 150mm , a height of 200mm; the diameter of the loading arm 1 is 25mm, and the height is 500mm, one end of which is vertically fixed to the center of the upper support member 3, and the other end is connected to the control execution system of the seabed detection equipment; four pore pressure sensors 5 are fixed on the ring In the four sensor holes on the shear plane 6; the four vertical hole pressure sensor leads 2 are connected with the four hole pressure sensors 5 and pass through the four sensor lead holes of the upper support member 3 to be respectively fixed with the loading arm 1 so as to be connected to the data collection system.

Technical analysis of the present invention:

Based on the comprehensive consideration of the actual installation and laying of the submarine pipeline and the normal operation process, the ring detector uses three equivalent analogies: the equivalent analogy of the submarine pipeline test process, the equivalent analogy of the detection equipment and the geometry of the submarine pipeline, and the detection equipment and Designed based on the equivalent analogy of the movement mode of the submarine pipeline, it can measure the undrained shear strength index (clay) and buried depth index required for the pipeline installation process, the consolidation settlement of the pipeline after installation, and the axial shear of the pipeline during operation Consolidation hardening index of stiffness and axial friction resistance.

1. Equivalent analogy treatment of submarine pipeline testing process:

Considering the drainage status of the shallow soil during the whole process from the laying and installation of the submarine pipeline to normal operation, the test process of the ring detector is equivalently divided into three stages (see Table 1 for details):

1) Pipeline installation stage: the actual pipe weight is replaced by the equivalent vertical load, usually the vertical penetration distance and time can be used to control the undrained condition during the installation process, and the initial pipeline buried depth during the installation process ;

2) Consolidation stage after pipeline installation: the actual consolidation pressure after pipeline installation (i.e. pipeline self-weight) is replaced by an equivalent vertical load. Specifically, after completing the 1) stage test, maintain the penetration to the target buried depth The corresponding vertical force at the position, waiting for the pore water pressure to completely dissipate;

3) In the normal operation stage of the pipeline: the thermal ratchet effect of the temperature stress during the actual pipeline operation is replaced by the alternating positive and negative circular shearing, and the degree of drainage during the shearing process is controlled by different shearing speeds, and the steering The residence time during forward and reverse switching controls the intermittent consolidation time.

Table 1 Equivalent treatment measures for the detection process of the ring detector

2. The equivalent analogy between the ring detector and the geometric size of the sea pipe:

Although it may be simpler and more intuitive to test relevant engineering parameters using a finite-length pipeline as the geometry of the detection equipment, due to the obvious end effect caused by continuous bulldozing at both ends during the axial shearing process, this paper The patent uses a circular shear surface to avoid the influence of the end effect on the detection results. However, the circular sounder designed based on this concept is different from the sea pipe in terms of structural shape, so it is necessary to make a reasonable equivalent analogy (see Table 2) for the parameters related to the geometric dimensions of the sea pipe (see Figure 1) in order to It is convenient to directly detect relevant engineering design parameters.

Table 2 Equivalent processing measures for ring detectors and sea pipes in terms of geometric dimensions

3. Equivalent analogy between ring detector and sea pipe movement:

The introduction of the design idea of the annular shear plane enables the axial motion of the real sea pipe to be equivalently compared with the axisymmetric rotational motion. The corresponding force analogy diagram is shown in Figure 1, and the vertical sea pipe motion does not need to go into the relevant analogy deal with. In addition, in different test processes, the corresponding equivalent analog parameters are shown in Table 3.

Table 3 Conversion of relevant parameters after the equivalent processing of the movement mode between the ring detector and the sea pipe

The present invention successfully converts the laying process of the submarine pipeline and the normal operation process in the later stage into the vertical penetration test and the rotary shear test of the ring detector by means of the above three equivalent analogy methods, and through effective data collection in the test The system records the penetration depth of the annular sounder, the subsidence level, the shear distance, the time response of the pore water pressure and the applied vertical load and the torque response of the shear in order to obtain the shallow soil required in the design of the marine pipeline. Key engineering design parameters such as shear strength index, consolidation coefficient index, and axial friction index.

Concrete investigation steps of the present invention are as follows:

1. Submerged installation process: ensure that the base frame supporting the test equipment is stably located at the predicted seabed position.

2. Test the engineering parameters of the submarine pipeline laying process:

1) Control the penetration speed of the circular detector to ensure that it maintains an undrained working condition during the penetration process. Usually, the penetration distance and time need to be set in advance in combination with the consolidation coefficient of the soil. This process adopts vertical displacement control. Time (t), vertical displacement (w), vertical bearing capacity (V) and pore water pressure (P) during the recording process;

2) It is best to repeat a set of penetration process, but switch to vertical force control, it is necessary to ensure that the vertical load applied to the ring detector is equivalent to the self-weight of the sea pipe in the specific project, so as to ensure the real working conditions. low normal stress state;

3) Keep the vertical force constant (V), wait for the pore water pressure to completely dissipate, and record the time (t), vertical displacement (w) and pore water pressure (P) during the consolidation process.

3. Test the engineering parameters of the normal operation process of the submarine pipeline:

1) The ring detector maintains a constant rotational shear angular velocity, and rotates clockwise and counterclockwise alternately (switch direction every 180 rotations), until there is no obvious change in pore water pressure;

2) The ring detector maintains a constant undrained rotational shear angular velocity, rotates clockwise and counterclockwise alternately (switching direction every 180 rotations), however, a dwell time is ensured each time the rotation direction is switched, so as to shear the pores generated Partial dissipation of the water pressure occurs until there is no appreciable change in pore water pressure.

Note: The selection of the constant rotation angular velocity needs to consider the consolidation coefficient of the soil in the actual project. The recommended value is 0.0179deg/s, and the corresponding working condition is that the initial buried depth of the submarine pipeline is 0.5D, and the soil is normally consolidated kaolin .

The invention not only can be used to investigate the axial movement mechanism of deep-sea pipe-soil and measure relevant engineering design parameters, but also is suitable for the related monitoring of the axial-pipe-soil effect of directly laying sea pipes in shallow sea without landfill. Considering the existing marine field survey technology and means, this equipment can use the offshore drilling platform to survey the undrained shear strength of shallow soil and the relevant consolidation indicators after pipeline laying (such as consolidation settlement, pore water pressure Dissipation conditions, etc.), the best implementation method should be combined with the survey ship in the early stage of the project, and carry out systematic pipe-soil surveys at intervals of 1-5 kilometers in the planned pipeline laying area (in relatively uniform geological areas, a larger measurement interval can be selected) Survey of axial action. First, the ring detector needs to be connected with the conventional marine geotechnical survey equipment through the loading arm (see loading arm 1 in Fig. Connect with the data acquisition system, and incorporate the four pore pressure sensors 5 installed at the bottom of the ring detector into the data acquisition system through the lead wire 2; at the same time, in order to ensure the stability of the penetration and rotation of the ring detector, the entire bottom ring is cut The surface 6 is connected by four cylindrical hollow tubes 4 and a circular support surface 3 on the top, and is fixed with the central loading arm 1 in a threaded manner; in addition, the annular shear surface 6 needs to be coated with an anti-corrosion protective layer and control the roughness of the surface The degree is consistent with the real submarine pipeline.

Claims (1)

1. An annular detector for the axial action of intelligent submarine pipeline soil, characterized in that: an upper support member made of aluminum alloy, an annular shear surface, four fixed rods, a loading arm, four pore pressure sensors and four The hole pressure sensor is composed of lead wires. The diameter of the upper support is 500mm and the thickness is 15mm. The upper support is evenly spaced with four fixing holes and four sensor lead holes. The diameter of the center circle of the eight holes is 400mm; the ring cut The surface is a solid structure, the bottom surface is a spherical surface with a diameter of 200mm, and the upper surface is a plane with an outer diameter of 500mm and an inner diameter of 300mm; four fixed holes and four sensor holes are evenly spaced on the annular shear surface, and eight holes The diameter of the center circle of the circumference is 400mm; the upper support and the annular shear surface are fixed by four vertical and evenly distributed fixed rods, the diameter of the fixed rods is 150mm, and the height is 200mm; the diameter of the loading arm is 25mm, and the height is 500mm. One end is fixed vertically to the center of the upper support, and the other end is connected to the control execution system of the seabed detection equipment; the four pore pressure sensors are fixed in the four sensor holes on the annular shear surface; the four vertical pore pressure sensor leads are connected to the The four pore pressure sensors are connected and passed through the four sensor lead holes of the upper support to be respectively fixed with the loading arm so as to be connected to the data acquisition system.