Coating apparatus – Projection or spray type – Projector combined with nonprojecting coater
Patent
1987-04-29
1988-10-04
Beck, Shrive
Coating apparatus
Projection or spray type
Projector combined with nonprojecting coater
118306, 118408, 118DIG10, 427236, B05B 1700, B05C 500
Patent
active
047749059
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to an apparatus for the internal coating of pipes having a first and second pig which engage the internal pipe surface and are movable through the pipe, having an intermediate zone between the two pigs for receiving coating material, whereby during the movement the pigs are pressurized and the coating material is forced out of the intermediate zone onto the internal surfaces of the pipe.
BACKGROUND OF THE INVENTION
In the chemical field, in particular in natural gas and oil transportation, water containing aggressive components (sulfur, salt) occurs in considerable quantities. This water is transported through welded steel pipes at times under very high pressures (up to 200 bar). If these are not isolated from the inside, they are destroyed by corrosion in a short time, which adversely affects the operation and considerably endangers the environment.
To reduce corrosion it has been suggested to install plastic tubes within the steel pipes. This, however, leads to an undesirable reduction of the pipe cross section.
For the prevention of this effect, it is known to coat the interior of pipes with material which is resistant to the accumulated aggressive media. This coating is carried out in pipes of large diameters by means of mobile vehicles which spray coating material.
This is not possible for pipes of small diameters. Instead, they may be coated, for example, by a package consisting of two pigs between which the in general fluid coating material is located, which is drawn back and forth through the pipe. Such a procedure has the disadvantage that the weak points which occur in the region of uneven parts of the internal pipe surface, particularly at the weld seams, where the coating material is stripped off by the second pig and thus form attack points for the aggressive media.
Another process for coating is airless paint spraying (the so-called airless-process). In this, the coating material from a tank located outside the pipe is pumped to a nozzle in the pipe by means of a high pressure pump and a high pressure tube. The high pressure in the tube causes the material to be sprayed and coat the internal surface of the pipe. The disadvantage of such a system is that, as a result of the considerable pressure loss caused by friction in the high pressure pipe only limited pipe lengths may be coated.
Even in oil and natural gas transportation, piplines are provided for the transport of required substances which may in parts extend underground for long stretches and so the new coatings of the inner tube surfaces required at regular yearly or half-yearly intervals causes a considerable expenditure. In order to effect the interval coating by one of the known apparatuses, stretches of about 300 m are dug up and the tube cut apart.
SUMMARY OF THE INVENTION
An object of the invention is therefore to provide an apparatus which enables very long thin pipes to be uniformly and reliably coated on the inside without permitting the coating to become too thin or completely broken at irregularities of the internal pipe surface.
This object is achieved by providing a spraying device which is movable through the pipe and which is connected to the intermediate zone between the pigs by means of a material feed line and the coating material from the intermediate zone is used for spraying.
By the use of such an apparatus, the coating material is carried along in the immediate vicinity of the spraying device so that practically no pressure loss takes place on the delivery to the spraying device; at the same time, the atomizing spraying device creates a non-contact, even inner coating of the pipe even at the weld seams and other uneven parts of the inner surface of the pipe.
Moreover, the pigs, which engage elastically with the pipe inner surface, spread the coating material located in the intermediate zone on the pipe inner surface as a thin base film so that pores and indentations that are difficult for the spraying device to access are already coated with the coating material when th
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patent: 2908248 (1959-10-01), Brant
patent: 3044136 (1962-07-01), Perkins
patent: 3058137 (1962-10-01), Doyle et al.
patent: 3125464 (1964-03-01), Harmes
patent: 3333311 (1967-08-01), Matheny et al.
patent: 3885521 (1975-05-01), Von Arx
patent: 4010712 (1977-03-01), Dugas
patent: 4329937 (1982-05-01), Holland
Bashore Alain
Beck Shrive
Hanschen Hermann
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