High pressure water jet cleaner and coating applicator

B-28833 2i:.17.~ i2 HIGH PRESSURE WATER JET CLEANER AND COATING APPLICATOR S TECHNICAL FIELD This invention relates to a device for treating the exterior surface of pipe in a pipeline, including cleaning, surface preparation and coating.

BACKGROt~ND OF THE INVENT~ A pipeline typically has an outer coating to protect the pipeline from corrosion and other detrimental effects, particularly when the pipeline is s buried underground.

This coating degrades with time, and, if the pipeline itself is to be prevented from sustaining further permanent damage, the pipeline must be dug up, the old coating removed, the surface of the pipe conditioned and a new coat of protective material applied to the pipeline.

When initially building a pipeline, the individual pipe sections are typlcally coated prior to shipment to the flnal locatlon, where they are welded togethar to form the pipeline.

By coatlng the plpe sectlons prlor to shlpment, it ls possible that the coatlng wlll be damaged ln shlpment.

Also, the welding of the pipe sectlons together destroys the coating at the welded ends.

Coatlng damage due to shipment and welding must be repaired on a spot basis as the pipeline is constructed.

Because of the excellent corrosion protection, impact and adhesive properties, it would be advantageous to coat the entire pipeline with a plural component polyurethane material at the construction site.

However, no technique has been developed to date to do so economicàlly and at the production rates required.

In a typical pipeline rehabilitatlon operatlon, the plpellne will be uncoverad, and a llfting mechanlsm, such as a crane, wlll be used to llft the exposed portion of the pipeline out of the ditch and rest the exposed pipeline on skids to provide access to the entire outer surface of the plpeline in the portion between the skids.

The plpe must then be cleaned, the outer surface of the pipeline prepared to receive a new protective coat, and the pipeline then recoated.

32~il7~7Z Initially, manual labor was required to remove the old coating with hand tools such as scrapers.

This technique is obviously time consuming and qulte expensive. various attempts have been made to provide more automation to the cleaning procedure, including U.S.

Patent No. 4,552,59g issued November 12, 1985 to van Voskuilen and U.S.

Patent No. 4,677,998 issued July 7, 1987 to the same inventor.

These patents disciose the use of high pressure water ~ets which are moved in a zigzag path along the plpe surface to be cleaned to slough off the coatlng.

While devlces of thls type have been an improvement over manual claaning, there stlll exists a need in the industry for enhanced performance in the cleanlng and recoating operatlon.

Zl, 17972 SUMMARY OF THE INVENTION In accordance with one aspect of the present lnvention, an apparatus is provided for treating a pipeline.

The apparatus includes a centering assembly mounted on the pipeline for movement along the pipeline. A nozzle carriage assembly is mounted on the centering assembly and defines at least one arcuate ring mounted thereon.

The centering assembly has at least one arm pivotally mounted to the centering assembly, wlth the arcuate rlng mounted on the arm.

The arm and ring are pivotal between a first position wlth the rlng concentrlc to the center axls of the pipellne and a second posltion spaced from the pipeline to allow the centerlng assembly and nozzle carriage lS assembly to be removed from the pipeline.

At least one spray nozzle is mounted on the arcuate rlng.

The spray nozzle can be mounted on the ring for reclprocatlng arcuate travel for a predetermlned arc along the arcuate rlng.

In accordance with another aspect of the present lnventlon, the spray nozzle can be used to spray a hlgh pressure water ~et to clean the plpellne, a comblnatlon of water and entralned abrasive for enhanced cleanlng and obtalnlng an angular surface proflle, or for applylng a plpe coatlng.

In accordance wlth another aspect of the present lnventlon, two arcuate rlngs are mounted on the noz~le carrlage assembly on opposlte sldes o~ the pipellne. A plurallty of spray nozzles are mounted on each arcuate rlng, each reclprocatlng through a predetermined arc.

Preferably, the.centerlng assembly and nozzle carriage assembly are moved along the plpellne at a veloclty that is one-half the width of each reciprocation path of the spray nozzle to cover the surface of the pipeline twice as the apparatus moves along the pipeline.

2' 1797Z BRIEF DESCRIPTION OF THE DRAwINGS For a more complete understanding of the present inve~tion and for further advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the accompanying drawings, in which:

FIGURE l is a side view of an automated pipeline treating apparatus forming a first embodiment of the present invention;

FIGURE 2 is a side view of the automated ~et cleaning unlt used in the apparatus of FIGURE l;

.FIGURE 3 is a front view of the automated ~et cleaning unit of FIGURE 2;

FIGURE 4 is a top view o~ the automated ~et cleaning unit of FIGURE 2;

FIGURE 5 is an end view of the nozzle carriage assembly and abrasive cleanlng nozzles utilized in the apparatus;

FIGURE 6 is an end view of the nozzle carriage assembly and abrasive cleanlng nozzles with the arcuate rings on which the nozzles are mounted pivoted to the removal position;

FIGURE 7 is an end view of the centering assembly used in the apparatus centered about a pipeline;

FIGURE 8 is an end view of the centering apparatus in the removal position;

FIGURE 9 is a schematlc vlew of the chaln drive for the abrasive cleaning nozzles ln the operatlng orientation, FIGURE 10 is an illustrative view of the chain drive in the removal position;

FIGVRE ll is an end v~ew of the nozzle carriage assembly and abrasive cleaning nozzles illustrating the chain drive;

Z; ;1~'37Z FIGURE 12 is a side view of the nozzle carriage assembly and abrasive cleaning nozzles;

FIGURE 13 is an illustrative view of the arcuate rings and abrasive cleaning nozzles in the operating position;

FIGURE 14 is an illustrative view of the arcuate rings pivoted to the removal position.

FIGURE 15 is an illustrative view of the nozzle used in the apparatus;

FTGURE 16 ls an illustrative view of the travel path of the spray from the nozzle;

FIGURE 17 i9 an end view of an automated pipeline trsating apparatus formlng a second embodlment of the present inventlon;

FIGURE 18 iS a slde view of the apparatus of FIGURE 17;

FIGURE 19 ls a slmpllfied end vlew of the apparatus of FIGURE 17;

FIGURE 20 is a simplified side view of the apparatus of FIGURE 17;

FIGURE 21 is an end view of the chaln drive of the apparatus of FIGURE 17;

FIGURE 22 ls a slde vlew of the chaln drlve of FIGURE 21;

FIGURE 23 ls an end vlew of a nozzle carriage and nozzle of the apparatus of FIGURE 17;

FIGURE 24 ls a slde view of the nozzle carrlage and nozzle of FIGURE 23;

FIGURE 25 ls an end view of the drive rlng assembly of the apparatus of FIGURE 17;

FIGURE 26 is an end view of a shield assembly in the apparatus of FIGURE 17; and FIGURE 27 is a side view of the shield assembly.

21; 1797Z DETAILED DESCRIPTION with reference now to the accompanying drawings, wherein like reference numerals designate like or similar parts throughout the several views, an automated pipeline treating apparatus 10 forming a first embodiment of the invention is illustrated in FIGURES 1-16.

The apparatus lo is used to clean and/or coat a pipeline 12, which can be either a new pipeline or a previously coated pipeline in need of rehabilitation.

Typically, the pipellne to be rehabilitated wlll be a pipeline which has ~ust been uncovered and raised out of the dltch wlth the orlginal coating on the plpellne ha~ing degrsded to a condition that 19 no longer serviceable.

In various modes of the apparatus 10, the apparatus can be used to clean any old coating off the pipeline and condition the outer surface of the pipeline itself for a new coating.

In another mode, the apparatus 10 can be used to spray on the new coating once the pipeline surface has been prepared.

In the cleanlng and surface preparation mode, the apparatus 10 includes three ma~or sections, a sled unit 14, a travel unlt 16 and an automated ~et cleaning unit 18.

The sled unit 14 ls commonly mounted on tracks which is pulled parallel to the pipeline being treated and the weight of the sled unit thus has no effect whatsoever on the plpellne.

In contrast, the travel unit 16 and automated ~et cleaning unlt 18 are supported on the pipellne itself for movement along the axis 20 of the pipe in the direction of arrow 22.

The weight of the travel unit and automated ~et cleaning unit will be such as to be readily carried by the pipeline without damage.

The weight of these units does not have to be supported by a side boom or other 3s lifting device during operation.

8 2.';17972 with reference to FIGURES 2-8, various details of the automated jet cleaning unit 18 can be further described.

The unit 18 includes a centering assembly 24. AS best shown in FIGURES 7 and 8, the centering assembly 24 can be seen to include pivotal arms 26 and 28 which pivot on frame member 30 through the action of hydraulic cylinders 32 between an operating position, shown in FIGURE 7, and an installation or removal position, shown in FIGURE 8.

Each of the arms, and the frame member mount an aligned pair of guide wheels 34 to support the centerlng assembly 24 on the pipeline.

In the operating position, as seen in FIGURE 7, the three pairs of guide wheels are dlstrlbuted at 120 from each othe~ around the pipeline so that the centering assembly 24 is centered on the pipeline.

preferably, air pressure is maintained ln cylinders 32 when the centering assembly is in the operating position to hold wheels 34 firmly against the pipeline to keep the centering assembly centered on the axis 20 of the plpe despite weld ~olnts and surface irregularities.

Attached to the centering assembly 24 is a nozzle carriage assembly 36.

The nozzle carriage assembly 36 lncludes two arcuate rlngs 38 and 40.

Ring 38 iS rlgidly secured to arm 26.

Ring 40 is similarly rigldly secured to arm 28.

Thus, as seen in FIGURE 6, as the cylinders 32 operate to pivot arms 26 and 28 lnto the installatlon or removal position, the arcuate rlngs 38 and 40 are slmilarly deployed.

As best seen ln FIGURE 4, the rings 38 and 40 are spaced apart a ~istance L from each other along the pipeline axis 20.

The rings preferably have an arc greater than 180-.

The radius of the rings 38 and 40 is selected so that the rings are concentric with the pipeline axis 20 when the arms 26 and 28 are in the 9 ;~ 1797Z operating position.

Thus, in the operating position, the rings 38 and 40 are at a constant distance from the outer surface of the pipeline about the entire circumference of the pipeline.

Mounted on the arcuate rings 38 and 40 are a series of abrasive cleaning nozzle carriages 42, with each carriage supporting an abrasive cleaning nozzle 44.

There are illustrated six carriages and nozzles on each of the rings 38 and 40.

However, this number can be varied as will be described in detail hereinafter.

Each of the carriages 42 is supported on a ring by a series of wheels 46 guided on the lnner and outer edges of the ring to permit the carriage and attached nozzle to move in an arcuate manner along the ring.

Each of the carriages on a partlcular ring are lnterconnected by links 48 pivoted between ad~acent carriages.

Thus, motlon of a carriage will be mirrored by the motlon of the rest of the carriages on that particular ring.

With reference to FIGURE 15, the details of the abraslve cleaning nozzles 44 can be descrlbed.

The nozzles have passages 50 to carry hlgh pressure water, for example in a pressure range of 10,000 - 15,000 psi.

An abraslve channel 52 carries abrasives ttyplcally sand) which are entrained in the water flow to enhance the cleaning act~vlty of the nozzle.

As can be seen, the high pressure water ls sprayed from the nozzle through ports 54 at an angle relative to the center axis 56 of the nozzla and toward the axls 56.

Thls creates a relative vacuum at passage 52 to entraln the abrasives in the water ~et flow to enhance the cleanlng action and provide an additional force to move the abrasive, As can be seen in FIGVRE 2, the abrasive nozzles 44 3s are preferably mounted on their carriages so that the lo ~:`17972 jet impinges on the outer surface of the pipeline at an oblique angle to the surface.

The nozzles are preferably adjustably mounted to allow the operator to select the ~est angle.

It has been found that this enhances the efficiency of cleaning.

The use of high pressure water jets, particularly with entrained abrasives, ls an improvement over shot blast cleaning, where shot impinges against the outer surface of the pipeline.

Shot blast cleaning leaves a relatively smooth outer surface to the pipeline, whlch is not a suitable surface profile for bonding with adhesive to apply a new coat on the pipeline.

The high pressure water ~et, particularly with entralned abraslves, generates a hlghly irregular angular surface whlch is very conducive for bondlng wlth adheslve.

With reference to FIGURES 9-12, the mechanism for oscillating the nozzles 44 will be described.

Mounted atop the centering assembly 24 is a control module 58.

Withln the control module is a motor 60 with a drive shaft 62 which extends out of the module and through the assembly 36 and extends parallel to the axis 20 of the pipeline when the units are in the operating position.

The motor rotates shaft 62 in the direction of the arrow with an ad~ustable predetermined angular velocity. A first drive gear 64 is mounted on the shaft ad;acent the ring 38. A second drive gear 66 is mounted on the shaft ad~acent the arcuate ring 40.

As seen in FIGURES 10 and 11, the first drlve gear drives a first driven gear 68 through a chaln 70.

The second drive gear drlves a second driven gear 72 through a chain 74.

Drive gears 68 and 72 are supported from frame member 30 so that the distance between the gears does not vary whether the arms are in the operating or installation and removal position.

ll z ,1797Z Arcuate ring 38 supports a continuous chain 76 which is supported about the periphery of the ring for 30O of the entire length of the ring.

Arcuate ring 40 s mounts a continuous chain 78 in the same manner.

First driven gear 68 drives a gear 80 which engages the chain 76 when the device is in the operating position as shown in FIGURE 9.

Second driven gear 72 similarly drlves a gear 82 which is engaged with chain 78 in the operating position.

When cylinders 32 are actuated to pivot arms 26 and 28 into the lnstallatlon/removal posltlon, the chalns 76 and 78 slmply move out of engagement with the gears 80 and 82, as best seen ln FIGURE 10, to disconnect the drlve traln.

Slmllarly, when the arms are plvoted to the operatlng posltlon, the chalns 76 and 78 re-engage the gears 80 and 82, respectlvely, to complete the drlve train.

In operation, the travel unit 16 wlll drive the cleaning unit 18 along the pipeline, while the motor 60 oscillates the nozzles 44.

Chains 76 and 78 each have a special llnk ln them whlch recelves a floating pin extendlng from the nozzle carrlage 42' closest to the drive motor.

The continuous rotatlon of chalns 76 and 78 translate lnto oscillation of nozzle carriage 42' about an arcuate distance on ring5 38 and 40 determlned by the length of the chalns 76 and 78.

The pin floats a llmited direction on a radlal line perpendicular to axis 22 when the arms and rings are in the operation position to follow the s~ecial llnk in lts travel.

If only a slngle nozzle carriage and nozzle were used on each ring, chains 76 and 78 need only be lengthened to extend about a 180 arc of the periphery of the rings, as shown in FIGURES 9 and 10.

1 2 7 9 7 2 As best seen in FIGURE 16, the width w that each nozzle travels should be twice the distance D that the nozzles moves along the pipeline.

Further, the arc of reciprocation for the nozzles should be about 360 divided by the number of nozzles to ensure complete coverage of the outer surface of the pipeline.

For example, if twelve nozzles are used, six on each of the rings, the arc of reciprocation should be 30O.

By following thls standard, every area on the pipellne will be covered twlce by nozzles as the apparatus moves along the pipeline to ensure cleaning of the pipeline.

Wlth such operation, a surface flnlsh of IS0 SA 2-1/2 should be possible with a highly angular surface profile of up to 0.00~ lnches in mean dlfferential to provide a superior base for a new coating.

The centering assembly 24 positions the nozzle carriage assembly 36 on the plpeline and ensures that the nozzles 44 malntain the proper standoff from the pipeline.

The control module 58 directs the flow of water and abrasive to the indlvidual nozzles and controls the oscillation of the nozzles. A two part cover 84 ls mounted on the arms 26 and 28 to overly the nozzles to protect the operator and other personnel from rlcochetlng water and abrasive spray.

The high speed water ~ets ln the nozzles accelerate the lndlvldual abraslve partlcles, typlcally sand, to greatly increase the momentum of the partlcle and allow it to more efficlently remove contamlnants on the pipellne surface and obtaln the needed surface proflle.

The high speed water ~et attacks the interface that bonds the coating or contamlnant to the pipe itself and removes all loosely bonded material.

In addition, the water will dissolve and remove any corros~on causing salts on the pipeline.

The erosive action of the abrasive is used to remove the tightly bonded material 13 2 ; 1 7 9 7 Z such as rust and primer and provide the desired surface profile for receiving a new coating.

The sled unit 14 is designed to be towed as a separate vehicle behind the travel unit 16 and cleaning unit 18 as they move along the pipeline.

The sled unit mounts the control panel for the various functions of the apparatus, and includes a computer to maintain the desired relation between speed of the units along the pipeline and the speed of oscillation of the nozzles.

The sled unit also contains high pressure pump units used to provide the high pressure water at nozzles 44.

One, two or three pumps can be run ln tandem dependlng on the size of the plpellne to be cleaned and the degree of cleaning desired.

Using less than the total number of pumps minimizes water consumption, fuel costs and malntenance when the full capacity is not required.

Also, in the event one of the pump units goes off line, another unit can be brought on line quickly to replace it. A quintuplex positive displacement pump with stainless steel fluid and pressure lubricated power ends is a satisfactory pump.

Such a pump can be rated at 10,000 psi at 34.3 gallons per minute, for example.

The sled unit also contains a compressor to operate the cylinders 32, a generator for electrical power for the motor 60 and to power the air compressor and other controls.

Also, the sled unit mounts containers of the abrasive to feed the cleanlng unit l~.

The chain drive and 9ingle dlrection rotatlng motor that oscillate the nozzles provide a smooth ramp up and ramp down of the nozzle operatlon at the ends of the nozzle path, not possible if a reversing motor is used to oscillate the nozzles.

The nozzles slow up smoothly as they reach the end of their oscillation arc and accelerate smoothly as they reverse their motion.

This provides a smooth operation.

As noted, for twelve 14 Zi j~ 7 9 7 Z nozzles, the arc of reciprocation should be 30O.

For ten nozzles, the arc should be about 36O.

Eor eight nozzles, the arc should be about 45O.

The apparatus 10 can be used to apply a new coating s to the pipeline as well.

Instead of nozzles 44 to apply abrasives and high pressure water ~ets, the nozzles 44 can be used to spray a polyurethane coating on to the pipeline. A polyurethane coating of the type that can be used for such coating is sold under the trademark and identification PROTOGOL UT 32 10 and is manufactured by T.I.B.-Chemie~ a company located ln Mannheim, West Germany.

Thls polyurethane materlal ls a two part materlal, one part b~lng a resin and the other an isocyanate.

When the two parts are mixed ln a 4 to 1 ratio of resin to isocyanate, the material sets up in a hard state wlthin thlrty seconds of mixing.

The apparatus 10 thus is an ideal device to apply such a spray in a continuous manner along the pipeline, providing, with the nozzle overlap, complete coating of the pipeline to the desired coatlng thickness as the apparatus moves along the pipeline.

After the polyurethane has been applled, solvent will be driven through the nozzles and supply passages to prevent the polyurethane from hardening and ruining the apparatus.

It is also possible to use only one oscillating nozzle per rlng to apply the coatlng by oscillating each nozzle 180' or so and moving the unit along the pipeline to insure complete coverage.

It is also possible to mount a plurality of nozzles in a fixed position on rings 35 and 40 for either cleaning or coating if oscillation is not desired.

Reference is now made to FIGURES 17-27 which illustrate a second embodiment of the present invention identified as automated pipeline treating apparatus 100.

Many of the components of apparatus 100 are 15 ~, 1797~ identical and work in the same manner as components of apparatus 10.

Those components are designated by the same reference numerals in FIGURES 17-27.

Apparatus loO is illustrated using only two nozzle carriage assemblies 36 and nozzles 44 in the apparatus.

n contrast to apparatus lo, the nozzle carriage assemblies lie in the same plane perpendicular to the axis 20 of the pipeline, instead of being staggered along the length of the pipeline as in apparatus 10.

This is made possible by providing a carriage mounting ring 102 on arm 26 and a carrlage mountlng rlng 104 on arm 28, with each rlng extendlng an arc of somewhat less than 180 so that there is no interference between the rlngs as the apparatus ls placed in the operatlng position. A chaln drive ring 106 is mounted to arm 26 ad~acent to carriage mounting ring 102. A simllar chain drlve ring 108 is mounted on arm 28 ad~acent to ring 104.

Rings 106 and 108 are also somewhat less than 180 in arc to avoid interference when the apparatus is in the operatlng position.

As best illustrated in FIGURES 23 and 24, the nozzle carriage assembly 110 is provided with four gulde wheels 112, two of which run on the lnner rlm of a carriage mounting ring, and the other two running on the outer rim of the carrlage mountlng rlng, to support the nozzle carriage assembly for arcuate motion along the ring.

The nozzle 114 ltself can be adapted for high pressure water ~et cleanlng using abrasives, as nozzle 44, or as a nozzle to distribute a pipellne coatlng such as the two part polyurethane mentloned prevlously. FIGURE 24 illustrates the mountlng of pin 116 on the carriage assembly 110 which is permitted to move a limited distance vertically as shown in FIGURE 24 as it follows the special link in the drive chain in 3s oscillation.

16 2.J~7.37~ with reference to FIGURE 25, the details of the chain drive ring 108 can be better described.

As only a single nozzle is mounted on the associated carrlage mounting ring, it will ~e desirable to have the nozzle carriage assembly and nozzle oscillate 180.

Thus, the continuous chain 118 mounted on the chain drive ring 108 extends about the entire periphery of the drive ring and is supported by tensioning wheels 120 and 122.

Guides 124 are also provided to guide the chain about the ring.

Wlth reference to FIGURES 21 and 22, the nozzle oscillatlng drlvlng elements of apparatus 100 are lllustrated.

The motor 60 drlves a slngle drlve gear 126 from lts drive shaft 62. A continuous chaln 128 connects drive gear 126 with driven gears 68 and 72.

Tensionlng gears 130 allow for tensioning of the chain.

It can be seen in apparatus 100 that the positioning of the rings 102 and 104 in a parallel plane permits a single drive gear 126 to operate the nozzles being oscillated.

With references to FIGURES 17-20, arm 26 can be seen to have parallel bars 132 and 134 extending from the arm parallel to the axis 20 of the pipeline which supports the nozzle carriage assembly 36.

Arm 28 has a similar pair of bars 136 and 138 which extend parallel the axis 20.

The chain drive rlngs 106 and 108 are supported on the bars through bracXets 140 whlch have cylindrical apertures 142 so that the rings can be slid over the bars and supported thereby.

The carriage mounting rings 102 and 104 have similar brackets 144 as best seen in FI~VRE 20.

To isolate the nozzle actlon from the remainder of the pipeline and apparatus other than that being treated, semi-circular annular plates 146 and 148 are mounted on arms 26 and 28, respectively, which lie in a 17 ~;~17972 plane perpendicular axis 20 and are closely fit around the outer circumference of the pipeline to isolate the components of the centering assembly from the portion 150 of the pipe being treated.

Each semi-circular annular plate includes a semi-cylindrical shield 152 which extends from the plate concentric with the pipeline radially inward of the carriage mounting rings, chain drive rings and nozzles.

An aperture 154 must be formed in the shield 152 at the position of each of the nozzles used so that the nozzles spray passes through the assoclated aperture to lmpact on the o~ter surface of the plpellne.

Where, as shown ln ' apparatus 100, the noz21es will move approxlmately 180, the aperture 154 must extend roughly a simllar arcuate dlstance.

Wlth reference to FIGURES 26 and 27, a two part shield assembly 156 including shield 158 and shield 160 are mounted on the bars 132-13B.

Shield 160 illustrated in FIGURES 26 and 27 can be seen to include wheels 162 for guiding the shield along bars 136 and 138.

The shield 160 lncludes a semlcylindrical concentric plate 164, and annular plates 166 and 168 which extend in a radlal dlrectlon from the axls 20 of the pipeline. A pneumatic double acting cylinder 170 is mounted on each of the arms 26 and 28 to move the shlelds 158 and 160 along the bars bet~een a flrst positlon 172 and a second positlon 174 as seen ln FIGU~E 18.

In the first positlon 172, the plate 164 flts concentrically wlthin the shields 152 and radially inward from the nozzles.

Thus, the shields 158 and 160 prevent either the high pressure water ~et or coating discharged from the nozzles from contacting the pipeline surface.

In the first position, the annular plates 166 and 168 prevent the discharge of the 3S nozzles from spraying either direction along the axis of the pipeline.

18 Zl;,l 7 9 7 2 In the second position 174, the shields 158 and 160 are moved to permit the nozzle spray to impact on the portion 150 of the pipeline being treated.

However, the annular plate 166 will prevent the spray from escaping from the apparatus in the direction of arrow 22.

The use of shield assembly 156 can have a number of benefits when coating a pipeline, for example.

It may be desirable to leave a short length of the pipeline uncoated, for example, at a weld, and thls can be achieved without stopping the motion or operation of the apparatus along the pipeline by simply drawing the shield assembly into the first position for a sufficlent period of time to prevent the coating over the deslred gap.

Once the gap ls passed, the shield assembly 156 ca~ be returned to the second posltion and coatlng of the pipeline can continue without lnterruption.

Although several embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the lnvention is not limited to the embodiments dlsclosed, but is capable of numerous rearrangements, modifications and substitutions of parts and elements without departing from the spirit and scope of the invention.