This invention is concerned with coating of pipes of the type used in subterranean or submerged pipelines for recovery of oil, gas, slurries or the like pipeable materials from a subterranean well. In particular it is concerned with pipes in which a steel pipe section is coated with an anti-corrosion coating and then a concrete aggregate anti-buoyancy coating (hereinafter concrete coating) . Such pipes normally include a mechanical shear transfer device in the form of wire windings or caging applied around the anti- corrosion coating prior to application of the concrete coating. This opposes the tendency of the concrete coating to slip or jump off the anti-corrosion coated pipe during laying operations which can impose considerable bending stresses upon the pipe, leading to loss of coating integrity.

Pipe coating methods addressing the problems of effectively applying a concrete coating to a pipe treated with an anti-corrosion coating are described, for example, in US-A- 3 955 600, GB-A-1 504 051, GB-A-1 504 052, GB-B- 2 088 992, GB-B-2 101 499, and EP-B-0 380 474 which are representative of the known art.

In a typical coating method uniform lengths of steel pipe are accumulated for coating and each in turn is lifted e.g. by overhead crane onto a bogie for individual coating treatment during which that length of pipe is caused to rotate about its longitudinal axis and passed longitudinally past a concrete coating station wherein concrete/aggregate is caused to impinge upon the rotating pipe thereby building up a thickness of concrete on the pipe to form a coating. Such a concrete coating can also be applied by other methods. The term "concrete" is used herein for brevity and convenience but will be understood by those in this art as referring to any weight coating consisting of a high density material delivered as a plastic mass for coating purposes, and which after coating forms a hardened coating. Preferred

weight or anti-buoyancy coatings may be applied to thicknesses of from about 40 mm to 150 mm or more and have a typical density of from 2165 to 3125 kg/m ³ by choosing appropriate mixtures of cement, sand and iron ore.

A disadvantage of known coating methods lies in the need to stop the concrete coating equipment applicator whilst a coated pipe is removed and a new pipe is brought in for treatment. This involves operation of cranes and movement of pipe carrying bogies which are time consuming and labour demanding activities. It is desirable to increase the efficiency of the coating process and reduce the period for which the coating equipment is inactive.

Accordingly an object of the present invention is to obviate or mitigate the aforesaid disadvantages and provide an improved pipe coating process.

This object is achieved by provision of an improved pipe handling system which enables the concrete coating equipment to be operated continually by carriage of pipes on bogies to and from a coating station in a cyclic pattern of operations such that as one pipe is coated and removed, another is sequentially brought in for coating automatically at a delivery rate which reduces interruption in coating activity to a minimum. The process is such that it may be set up to run automatically according to a computer controlled programme of operations. However in practice, for safety reasons, it is anticipated that the entire operation of delivery, coating and removal of treated pipes can be supervised and controlled by a single operative.

According to the present invention apparatus for coating pipes with concrete comprises a concrete coating station, a plurality of mobile pipe carriers having means for facilitating rotation of a pipe supported thereon, and means for sequentially advancing said pipe carriers in continual succession past the concrete coating station to

convey pipes to and from said station for the purposes of applying a concrete coating thereto.

Preferably, the mobile pipe carriers are self-propelled remote-controlled vehicles having means for adjustment to provide adjustable support length to accomodate differing lengths of pipe. Preferably also said carriers comprise pipe end supports mounted on rail guided bogies. At least one of said pipe end supports comprises a driven roller to facilitate turning of the pipe when carried upon the carrier for coating purposes. Corresponding idler rollers in the end supports are provided as required to achieve the required rotation of the pipe when supported in the carrier. In this way the pipe to be coated is cradled by its ends upon the rollers in a manner generally known per se in this art.

The most preferred arrangement provides for parallel tracks of paired rails and transfer sections to enable crossover between said tracks, a first track having a section passing before the concrete coating station to allow a carrier to present a pipe for coating on that first track and subsequently pass over a transfer section to allow that carrier to be returned for re-loading on a second track. Preferably the transfer section comprises a sliding section of track which is displaceable laterally at right angles to the track length or normal direction of travel to bring that section into correspondence with a second track parallel to the first track. Preferably also a pipe off-loading device is provided in proximity to the transfer section for removal of a coated pipe from the carrier.

In this arrangement according to the invention a loaded carrier advanced before the concrete coating station in one direction can be unloaded after the pipe coating operation whilst a following loaded carrier advances before the concrete coating station, the unloaded carrier is returned via a track by-passing the concrete coating station to be

re-loaded, the whole operation repeating in an essentially uninterrupted cycle which provides the advantage that the concrete coating station may be operated continually.

An embodiment of the invention will now be described with reference to the accompanying drawings in which:

Fig. 1 is a perspective view of a pipe prepared for coating and supported on a rail-guided carrier for delivery to a concrete coating station; Fig. 2 is a perspective view of another carrier identical to and immediately ahead of that carrier shown in Fig. 1 the carrier bearing a pipe in the process of being coated and treated at the concrete coating station; Fig. 3 is a perspective view of a pipe unloading device for off-loading coated and treated pipes from the carriers, which device cooperates with an overhead crane for transporting said pipes to a despatch or storage area (not shown) ; and Fig. 4 is a perspective view of an empty carrier being returned for loading and by-passing the concrete coating station where a pipe is being coated.

A pipe coating apparatus comprises a concrete coating station 1 having a conveyor belt 2 for delivery of a coating material fed from a hopper 3 at a sufficient rate to cause that material to impinge upon a pipe presented before it . The pipe is delivered for coating upon a carrier 4 comprising longitudinally extending frame members 5 having rail guided bogies 6 located at either end. Pipe support means 7 mounted above the bogies provides paired rollers 8, 9 located so that each pair contacts an end of a pipe. At least one of these rollers is driven in order to turn the pipe during a coating operation and one in each pair (9) has a flange 10 for retaining the pipe in position upon the carrier and avoid it riding off the rollers along its longitudinal axis as it is being turned during coating. The

carriers are rail guided and remotely controlled self- propelled vehicles. The rails upon which the carriers travel form two parallel tracks 11, 12 having portions passing before the concrete coating station. That track (11) closer to the station provides for advancement of a pipe to be coated and treated at that station past the conveyor belt 2 and that (12) which is further from the station provides for return of empty carriers. The tracks are provided with transfer or crossover sections 13, 13'; 14, 14' to enable the carriers to be passed from one track to the other quickly and with minimum length of track being used. The preferred transfer section consists of paired sections of track which are displaceable laterally from a first position in line with track 11 to a second position corresponding to track 12. Interposed between one of said paired sections (14, 14') is a pipe handling device 15 for off-loading coated pipes onto cradles 16, 16' . This device has a curved support plate 19 fixed between a pair of elevatable counter-balanced booms 20 supported on pivots 21 on a frame 22 which is also mounted upon rails 18, 18" arranged at right angles to the track 11 so that the device may advance towards the track to lift a coated pipe from a carrier and -retire to an off-loading position between said cradles.

In use a pipe prepared for coating is lifted e.g. by overhead crane, from a store of such pipes (not shown) onto a carrier 4 which is activated and advanced along the track towards the concrete coating station 1. As the carrier passes the station the driven roller(s) are actuated to cause the pipe to rotate at a predetermined speed about its longitudinal axis . The coating station is operated to cause coating material e.g. concrete having a density of about say 2645 kg/m based on Ilmenite to impinge at a relatively high velocity onto the pipe, the delivery rate being selectively variable in the range of from about 2000 kg/min. to about 4000 kg/min. depending upon the desired coating thickness. Additional treatments may be applied simultaneously e.g.

through spray nozzle 17. This tried and tested method of coating pipes provides an effective even coating of concrete upon the pipe. As the coated pipe is conveyed away by the carrier, a further carrier is already immediately queued behind for presentation of a further pipe for coating so that the coating station can be operated continually. As the further carrier passes the coating station the first is already before the off-loading station where the pipe handling device 16 advances to lift the coated pipe off the carrier, and subsequently retire to rest the coated pipe on cradles 16 for pick up by an overhead crane or like device. The empty carrier is already stationed over the transfer sections 14, 14' and operation of the control mechanism causes sliding of these sections of track 11 to be displaced laterally at right angles to the track direction to bring these sections into correspondence with the second track 12 parallel to the first track, whereupon the carrier is driven in the reverse direction to back track for re-loading whilst by-passing the subsequent carriers now passing before the concrete coating station. This translational motion of the paired track sections operates both at the loading and unloading stages of the coating operation and provides for rapid delivery of carrier borne pipes with minimum use of track length and number of carriers such that the carriers can be queued before the coating station as a substantially continuous train of pipes which enables the coating plant to be continually operated. This minimises downtime and labout intensive operations encountered with prior art methods and apparatus .