GB2523235A - A device for measuring cathodic potential of a coated metal surface - Google Patents

Abstract

An ROV-operated assembly 1 includes a probe 11 provided with a probe tip 1111 arranged to penetrate a protective layer (31, Fig 5) on a metallic object (3, Fig 5). A hammer unit 14 is arranged to impart an axial motion to the probe tip where the axial motion is a reciprocating one induced by the rotation of an input driveshaft in the hammer unit. The motion may be generated by rotating a rotor with a corrugated face which rests against a complementary face of an axially displaceable non-rotatable rod connected to the probe tip. An alternative arrangement provides the rotor with a jacket having a continuous groove and a corresponding guiding element on the non-rotatable rod. The probe can be used to measure the cathodic potential of a coated metal surface by piercing the coating.

Description

A DEVICE FOR MEASURING CATHODIC POTENTIAL OF A COATED METAL SURFACE

The invention relates to an ROy-operated assembly comprising a probe provided with a probe tip arranged to penetrate a protective layer on a metallic structure.

Measuring cathodic potentials (CP measurements -Cathodic Potential Measurement) is a type of non-destructive measurement which has for its purpose to measure the level of the cathodic protection of a chosen underwater structure. The measurement is carried out by the metal tip of a CP probe being placed in contact with bare metal at the desired place of measuring, and an electrical-voltage value being recorded. The probe tip must be in contact with the metal for a time period of minimum 2-3 seconds for a measurement to be correct. Measuring on an underwater structure is typically carried out by the CP probe being manipulated by a remote-controlled underwater vehicle (ROV) or a diver.

In some structures, it has turned out that the paint coating is very thick, and this re-sults in it being difficult to stab the tip of the CP probe through the layer of paint and into the metal. This means that because of its limited weight and lack of a manipula-tor, especially an observation ROy, that is to say an ROV arranged for observation (OROV -Observation Remote-Operated Vehicle), has problems in carrying out the necessary measurements. On a work ROy, that is to say an ROV arranged to perform work (WROV -Work Remote-Operated Vehicle), the CP probe is manipulated by a manipulator arm, whereas on the OROV, the CP probe is directly attached to the vehi-cle by means of a bracket. To compensate for the lack of weight when generating an impact force, the OROV is generally moved at relatively great speed towards the structure to drive the CP probe through the paint coating. In some cases, this has to be repeated several times before the CP probe has achieved contact with the metal.

Often, the CP-probe tip bounces back out at the moment of collision, so that a suffi-ciently long contact time with bare metal is not achieved.

An unfortunate consequence of today's practice is, among other things, the following: The vehicle is subjected to repeated concussive impact strains as the CP probe is brought against the structure, resulting in: Components, for example electrical contacts, coming loose.

Light bulbs being broken.

S Faults arising in electronic components, for example loose contacts in circuit LJUdI US.

Threaded connections being ruined.

Covers cracking.

* The front portion of the ROV (camera, lights, transponders, covers and so on) so is damaged in consequence of the Cl' probe not hitting the target and the front portion of the ROV colliding with the structure.

* Heavy wear on the CP-probe tip as it is repeatedly knocked against the struc-ture.

* An OROV takes a relatively long time on one single measurement.

* A sufficient measurement quality is not achieved.

* Interruptions in other operations, in consequence of a WROV having to assist an OROV to complete a CP measurement, create delays and lost operation time.

* A possible move of a surface vessel to improve access for the WROV results in lost operation time.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

A CP-probe holder provided with a vibration or impact function is provided, setting the CP probe in an axial motion that makes a CP-probe tip penetrate a paint coating while an Roy, to which the Cl' probe is attached, is pressing with an even machine force against a structure surrounding a measuring point. The Cl' probe is connected to a Cl'- probe holder via a hammer unit that provides the vibration or impact function when-ever needed.

To create the desired vibration or impact effect required for the CP tip to penetrate the paint coating, the following solutions may be applied for the hammer unit: * A mechanical impact function of the same type as, for example, in an "emer-gency hammer", namely a spring-loaded hammer being tensioned, a release mechanism being operated so that the hammer is released, and a tensioned spring forcing the hammer to strike against a structure. An electromagnet may be arranged in order to, whenever necessary, tension the hammer for another blow.

* An electromagnet causes repeated impact pulses in an actuator element by pulling, or pushing, the actuator element in its longitudinal direction at a suita-ble frequency.

* A rotatable, axially fixed element with the same function as a hammer drill, as two circular plates are each provided with a corrugated end face, which rest against each other and create axial vibration when one plate is rotated and the other is kept stationary.

-A,,--.f-.I-'I -b.II'. Fh.,.A.-.-,;,4aA *,ifk i r,arLnnFk n rnr,anrrnnnnd -fl I JLClLLlJI, Ciflitlily I Ii%A _I_I II..I IL JVfl.4%_..I VYI.II.a.a, circumferentially, and an encircling, non-rotating and axially displaceable sleeve engaged with the curved-path groove via one or more guiding elements.

The curved-path groove provides for the sleeve to be forcedly guided in both axial directions.

* A vibrator like that of a mobile phone, a steamroller or a concrete vibrator, in which the vibration is provided by rotating a weight with its centre of gravity outside the axis of rotation at great speed.

In a preferred embodiment, a hammer unit is provided, arranged between a driving motor and the CP probe, preferably fixed in the CP-probe holder. An advantage of ar-ranging the hammer unit outside the driving motor is that the driving motor may then be shielded from unfavourable impact and vibration strains from the hammer unit.

This is achieved by the hammer unit being fixed in the CP-probe holder, so that, for example, a flexible coupling can be used between the driving motor and the hammer unit, or by the driving motor being fixed in the CP-probe holder by means of flexible motor attachments.

The hammer unit provides a rotationally induced, axial, non-rotating motion of the CP-probe tip, as the motor output driveshaft of the driving motor is connected to an input driveshaft of the hammer unit, whereas the CP-probe tip is connected to an axially n mnvahI niitniit mt-I r.f thn hammr init Thn rnt-atinnI mntinn inniit is converted to an -----.---axially reciprocating motion output by the input driveshaft of the hammer unit being connected in a rotationally rigid manner to a rotor with a corrugated end face facing a corresponding end face of a disc-shaped, non-rotatable and axially movable agitator connected to the output rod of the hammer unit. The corrugated end faces are com-os plementary and may be provided with teeth extending in the radial direction of the end faces and preferably having a triangular cross section, that is to say having plane tooth faces. The rotor of the input driveshaft is axially and radially supported in a housing, whereas the agitator of the output rod is radially supported in the housing.

In a more preferred embodiment, the hammer unit is formed with an input driveshaft connected in a rotationally rigid manner to a circular rotor provided with a curved-path s groove arranged on the jacket surface of the rotor. The rotor is axially and radially supported in the housing. An annularly encircling, non-rotatable agitator is provided with one or more guiding elements projecting into the curved-path groove on the rotor and is axially displaceable in the housing according to the axial extent of the curved path. The agitator is connected to the output rod of the hammer unit for the transmis-Ic Sian of the reciprocating motion to the CP-probe tip.

The invention relates more specifically to an Roy-operated assembly including a probe provided with a probe tip arranged to penetrate a protective layer on a metallic object, characterized by a hammer unit being arranged for the probe tip, arranged to impart an axial motion to the probe tip.

The axial motion of the probe tip may be a reciprocating one and induced by rotation of an input driveshaft in the hammer unit.

The hammer unit may be arranged between the probe and a driving motor.

An input driveshaft, which is connected to a driving motor may be provided with a rotor including a corrugated end face which rests, in an active position, against a com-plementary end face of an axially displaceable, non-rotatable rod connected to the probe tip.

The rod may be connected to a damping device, which, in the non-loaded state of the assembly, provides a clearance between the end faces of the rotor and the rod.

An input driveshaft, which is connected to a driving motor may be provided with a rotor including a jacket surface provided with a continuous curved-path groove, and an agitator which is connected to the probe tip via an axially displaceable, non-rotatable rod may be provided with a guiding element which is in engagement with the curved-path groove.

The CP-probe assembly may be attached to an observation ROV.

o In what follows, an example of a preferred embodiment is described, which is visual-ized in the accompanying drawings, in which: Figure 1 shows a CP-probe assembly according to the invention in perspective; Figure 2 shows an axial section on a larger scale through a first embodiment of a hammer unit; Figure 3 shows an axial section through a second embodiment of the hammer unit; Figure 4 shows, in perspective, a rotor for an input driveshaft in the hammer unit as shown in figure 3; and Figure 5 shows a side view on a smaller scale of a CP-probe assembly according to the invention connected to an observation remote-controlled under-water vehicle (observation ROV) in an operative position at a structure that is the object of measurement.

Reference is first made to figure 1, in which the reference numeral 1 indicates a CP-probe assembly including a CP probe 11 connected to the output driveshaft 121 of a driving motor 12 via a flexible driving clutch 13 and a hammer unit 14. Said units 12, 13, 14 are attached to a frame 15.

The CP probe 11 includes a probe body 111 and a mounting sleeve 112 and is at- tached in an axially displaceable manner to the frame 15 by means of frame attach-ments 114. A leading portion of the probe body 111 forms a probe tip 1111 according to the prior art known per Se. The CP probe 11 is provided with a signal cable 113 ar-ranged to transmit measuring results to a signal processor not shown.

Reference is now made to figure 2. Tn a first exemplary embodiment of the hammer unit 14, an input driveshaft 141 is axially rigidly supported in a housing 146 and pro-vided with a rotor 142 arranged in the housing 146. The rotor 142 is provided with a corrugated end face 1423, which may rest against a complementary end face 1451 of a non-rotatable, axially displaceable rod 145 that projects out of the housing 146 in a direction away from the driveshaft 141. A damping device 1452 is arranged to provide a clearance between the corrugated end faces 1423, 1451 of the rotor 142 and the rod 145 in the non-loaded state of the assembly 1. when the probe tip 1111 is pressed against a structure (see figure 5), the probe 111 and the rod 145 are pushed 36 backwards, the damping device 1452 being compressed and the end faces 1423, 1451 achieving contact with each other so that vibration arises in the probe tip 1111 when the driveshaft 141 rotates.

The housing 146 is provided with at least one evacuation opening 1461, which con- nects the interior of the housing 146 to the surroundings. The purpose of the evacua-tion opening(s) 1461 is to prevent a pressure build-up inside the housing 146 as the rod 145 is being moved towards the rotor 142.

Reference is now made to figures 3 and 4, in which a second exemplary embodiment of the hammer unit 14 includes an input driveshaft 141 with a rotor 142 in which, in a jacket surface 1421, a continuous curved-path groove 1422 is arranged. An agitator 143 encircling the rotor 142 is provided with a guiding element 144 projecting into the curved-path groove 1422. End portions 1431 of the agitator 143 project through the is end face of the housing 146 where the agitator 143 is connected to the rod 145. In this embodiment the rotor 142 forcingly drives the rod 145 as the guiding element(s) 144 of the agitator 143 follow(s) the curved-path groove 1422 during the rotation of the rotor 142.

Even though the forced-driving properties of this embodiment are less sensitive to a is pressure build-up in the housing 146, the housing 146 is provided with at least one evacuation opening 1461 in this embodiment as well, for the housing 146 to be evac-uated when the agitator 143 is displaced axially in the housing 146 by the rotation of the input driveshaft 141.

Reference is now made to figure 5, which shows the CP-probe assembly 1 attached to an observation ROV 2 provided with a propulsion arrangement 21 known per Se. The propulsion arrangement 21 pushes the ROV 2 towards a metallic structure 3, which is to be checked. The driving motor 12 of the CP-probe assembly 1 is started so that a reciprocating motion is induced in the probe tip 1111. The repeated displacements or impacts of the probe tip 1111 against the protective layer 31 of the metallic structure 2 3 make the probe tip 1111 penetrate through the protective layer 31 into metallic con-tact so that a reliable collecting of measuring data can be carried out by means of the probe 11.

Claims (6)

1. claims 1. An ROy-operated assembly (1) including a probe (11) provided with a probe tip (1111) arranged to penetrate a protective layer (31) on a metallic struc-ture(3), characterized in thatahammerunit(14)is arranged for the probe tip (1111), arranged to impart an axial motion to the probe tip (1111); and the axial motion of the probe tip (111) is a reciprocat-ing one and is induced by the rotation of an input driveshaft (141) in the hammer unit (14).
2. 2. An ROy-operated assembly (1) according to claim 1, wherein the hammer io unit (14) is arranged between the probe (11) and a driving motor (12).
3. 3. An ROy-operated assembly (1) according to claim 1, wherein an input driveshaft (141) which is connected to a driving motor (12) is provide with a rotor (142) including a corrugated end face (1423) which rests, in an active position, against a complementary end face (1451) of an axially displacea-is ble, non-rotatable rod (145) connected to the probe tip (1111).
4. 4. An ROy-operated assembly (1) according to claim 3, wherein the rod (145) is connected to a damping device (1452) which, in the non-loaded state of the assembly (1), provides a clearance between the end faces (1423, 1451) of the rotor (142 and the rod (145).
5. 5. An ROy-operated assembly (1) according to claim 1, wherein an input driveshaft (141), which is connected to a driving motor (12) is provided with a rotor (142) including a jacket surface (1421) provided with a continuous curved-path groove (1422), and an agitator (143) which is connected to the probe tip (1111) via an axially displaceable, non-rotatable rod (145) is pro- vided with a guiding element (144) which is in engagement with the curved-path groove (1422).
6. 6. An ROy-operated assembly (1) according to claim 1, wherein the assembly (1) is attached to an observation ROV (2).