CN1054134A - Defect detector for foam plastic anticorrosion insulating layer of steel pipe - Google Patents

Abstract

Defect detector for foam plastic anticorrosion insulating layer of steel pipe provided by the invention is the defects detection instrument that is used for the foam insulation of steel pipe and interlayer.This detector is to drive capacitive transducer by the travel mechanism that direct current generator drives to move on tested pipeline, the rational data processing of rate of change process by electric capacity, judge the quality of foam heat-insulation layer with this, and demonstrate pipe insulating layer by display system and do not have residual or have residually, and accurately show the position in residual district.This instrument is easy to use, and good reliability is convenient to manufacturer's rapid batch product is detected.

Description

Defect detector for foam plastic anticorrosion insulating layer of steel pipe

In industries such as oil delivery, be extensive use of the steel pipe of foam plastic anticorrosion insulating layer, its structure is as shown in Figure 1; Steel tube core (1) froth bed (2) folder shell (3).Wherein the about 5cm of foam bed thickness mainly plays the insulation antiseptic effect, the thick 0.5cm of folder shell, and have certain intensity, have the effect of rainproof damp proof insulation and protection froth bed.Owing to foam after production run is inserted in steel pipe in the interlayer, scarce dangers such as cavity that volume do not wait and crackle appear in froth bed unavoidably, because froth bed is clipped between shell and the steel pipe, its defective can't macroscopic examination, and they cause very big threat to the safe handling of pipeline.

Up to the present, still not having specialized equipment both at home and abroad detects effectively to this defective.Domestic manufacturer adopts analysis directly perceived and the method for manually knocking to carry out quality check.Preceding kind method is destructive, and loss is big, and efficient is low, can only carry out minimum bulk sampling inspection, can't satisfy the importantly quality requirements of segment pipe laying.Manually knock determination methods because pipeline outer-layer plastic clip shell and froth bed are usually thrown off, and there have space, the 1cm left and right sides, this situation hammering method to be easy to erroneous judgement to be disconnected.

The object of the present invention is to provide a kind of defect detector for foam plastic anticorrosion insulating layer of steel pipe, this detector can be easily detects and the position at display defect place the quality of the froth bed in the folder shell of pipeline.

Detecting instrument provided by the invention is to drive capacitive transducer by travel mechanism to move on tested pipeline, the rational data processing of rate of change process by electric capacity, judge the quality of foam heat-insulation layer with this, and demonstrate pipe insulating layer by display system and do not have residual or have residually, and accurately show the position in residual district.

Detecting instrument provided by the invention mainly is made up of following 3 parts: detection ring and display part, the signal other part of breaking, travel mechanism.

1。Detection ring and display part:

Detection ring is that probe (5) by 12 capacitive transducers independent of each other surrounds a ring texture equably as shown in Figure 2, and pincers are enclosed within (4) in the shell, and each sensor probe is made up of movable plate electrode, C/f change-over circuit and the spacious cover of pole plate screen three parts.Steel pipe is as the public static plate electrode of capacitive transducer.Detection ring by can open, two closed semi-rings form.During detection ring set is opened, retaining ring is outside pipe to be measured, and each sensor keeps excellent contact with tube wall under the effect of spring.Movable plate electrode is made by copper clad plate.Though the principle of capacitive transducer is simple, its antijamming capability very a little less than, when especially a plurality of capacitor plates were arranged in parallel, the influence between was more obvious mutually.Therefore, each movable plate electrode all is provided with a spacious cover of being made by sheet metal of screen, to reduce the phase mutual interference of electric field between each pole plate as far as possible.Each capacitance probe is all with the C/f change-over circuit, as shown in Figure 3.

On the detection ring, all there is the corresponding indication of two signal lamps (6) defective locations at each probe two ends, and anchor ring also is distributed with four greensignal lights (7) as the no indication when residual, and signal is differentiated on the cabinet partly the warning of hummer as residual district is housed.

2. signal is differentiated part

Shown in system chart (Fig. 3), this instrument is provided with 12 capacitance probes altogether, for each probe one cover electric capacity/frequency (C/f) change-over circuit is arranged, 12 road frequency signals are sent into main frame, micro-processor controlled 12 path analoging switch are selected 1 tunnel in 12 road signals to send into frequency/digital conversion circuit (f/D conversion) successively and are sampled.The f/D change-over circuit has adopted a kind of high-speed, high precision conversion method of semiperiod counting, and its theory diagram is seen Fig. 4 a, and Fig. 4 b is its sequential.As seen from the figure, this transfer process is not the output signal TS of direct census capacitive transducer ₁, but the frequency of being exported by 74LS14 and 10MHZ quartz oscillator in the time semiperiod inside counting of TS is the fo signal of 10MHZ, and the T of the direct control counter of TS allows end, and this has just guaranteed the accuracy of conversion.And the stability of quartz oscillator output signal fo is unchallenged, and drift only is 2H _ZCLR, the PS signal is controlled by microcomputor program, is exported by output interface 74LS77.Each conversion is sent the PS signal more earlier to 34 digit counter 74LS161 counter O reset, and it guarantees that counter is not to the more than one semiperiod counting of TS signal.The N of Fig. 4 b is the fo umber of pulse that counter counts, and it converts 12 bit digital quantity to by counter, through input interface input microcomputer.

In order to improve the f/D conversion accuracy, the TS signal is to be obtained by sensor output signal eight frequency divisions.The digital signal after the derivation conversion and the relation of frequency signal:

N＝4fo/f

If f=16kH _Z, N=2500 then

Simultaneously: dN=-(4fo)/(f ²) df

F increased 3QH when heat-insulation layer had the cavity _ZCan draw digital quantity by following formula and reduce 5.In addition, to single pole plate, the average sample time of unitary sampling is

to＝38Qμs

From above analysis as can be known, adopt the semiperiod method of counting, than direct census sensor output signal, its conversion accuracy and speed all are greatly improved.These deposit data are carried out data processing by microcomputer then in random access memory 6116.

Because detector is to detect in walking, the walking of machinery vibration, will cause capacitance probe sound polar plate spacing from variation, the capacitive transducer output signal is caused very big interference, if do not add any processing, directly carry out analysis and judgement with it, then can not get correct result at all.Must carry out a series of data processing to signal with microcomputer.Simultaneously, owing to designed aforesaid high speed f/D conversion method, can sample in a large number to signal, for data processing provides the foundation.

Each analysis and judgement is to each pole plate sampling 12 times, during this period, detection ring moves forward 4mm, and making 12 samplings is not on a fixed position of pipeline, but be distributed on the such slight distance of 4mm the more real actual conditions that reflect heat-insulation layer of these signals.

First order filtering is that maximal value and minimum value in each sensor 12 sampled value are removed, and the gross error of initial sampled value can be removed generally speaking.Through experimental test and analysis, undesired signal is a radio-frequency component, and what filtering was for the second time adopted is the low pass average filter, ten remaining initial sampled value additions, as total sampled value of the n time sampling.Note is made Mn, in filtering, signal amplitude has been strengthened like this.In order to process, adopted the three term recurrence average filter of the third level again to signal is further level and smooth:

$\mathrm{Mn}=\frac{1}{3}\underset{i=1}{\overset{3}{\mathrm{\Σ}}}\mathrm{Mn}-(i-1)$

Signal can reflect the situation of tested pipeline heat-insulation layer basically through such three stages of digital filtering, calculates the rate of change of electric capacity on this basis:

△M＝M _n+1-M _n

According to the size of △ M, just can judge whether defectiveness occurs.

Fig. 5 is the C/f change-over circuit, and Fig. 6 is an I/O plate schematic diagram, and Fig. 7 is 280-CPU mainboard figure.

3. travel mechanism

The detection of corrosion-resistant thermal insulation layer defects is undertaken by detection ring dynamic walking on pipeline, and its driving mechanism is to walk car (9) again by walking car drive detection ring (10) realization testing goal by direct current generator by the traction of wire rope (8).When detection ring hung over the enterprising action attitude of walking car and detects, its synoptic diagram was seen Fig. 8 near motor power placed motor.

When detecting, detection ring is enclosed within on the pipe under test, mainframe box and stabilized voltage supply branch hang over both sides.At first select K ₁-K ₄(see figure 6) presets accuracy of detection.The energising back is by reset key, and this moment, program began to automatically perform, by the system controlled by computer testing process.Because four function keys on the switch: walking, detect, residually walk, be reversed control.

The forward of the strong control detection ring of walking is walked or is stopped, and is the necessary condition that detects.Detect the key decision and when begin to detect, at this moment, program will be followed back production sample, analysis and judgement to No. 12 sensors, if find defective, will provide that detection ring stops, the respective regions red light is bright and output information such as audible alarm, and the original place products for further is handled.The residual key of walking is after residual parking is arranged, the control detection ring, and the detection that walks in residual district, after residual end of extent, detection ring stops once again automatically, and corresponding red light goes out, and indicates residual end of extent, afterwards, if lift the residual key of walking, will proceed normal detection.The reflection key is the oppositely walking of control detection ring.

Defect detector for foam plastic anticorrosion insulating layer of steel pipe provided by the invention provides reliable detection method for this detection.This instrument is easy to use, and good reliability is convenient to manufacturer's rapid batch product is detected.

Claims (3)

1, a kind of defect detector for foam plastic anticorrosion insulating layer of steel pipe is characterized in that the detection ring that is driven by travel mechanism moves on tested pipeline, the rate of change of its electric capacity is differentiated part through signal and is carried out data processing, show the no residual of heat-insulation layer and have residual, described by display system:

The A detection ring surrounds openable ring texture by 12 capacitive transducer probes independent of each other [5], and each sensor probe is made up of movable plate electrode, the spacious cover of c/f change-over circuit pole plate screen

It is the f of 10MHZ in the inside counting of time semiperiod by 74LSi4 and 10MHZ quartz oscillator output frequency through the frequency signal of c/f change-over circuit output by capacitive transducer that the B signal is differentiated part.Signal converts 12 bit digital quantity to by counter.

2, defect detector for foam plastic anticorrosion insulating layer of steel pipe according to claim 1 is characterized in that the movable plate electrode of capacitive transducer probe made by copper clad plate, and steel pipe is as the common public static plate electrode of capacitive transducer.

3, defect detector for foam plastic anticorrosion insulating layer of steel pipe according to claim 1 is characterized in that being detected by walking car drive detection ring (10) by the tractor (9) of direct current generator by wire rope (8) again.

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