New field joint Coating system for trenchless laid steel pipes
Feb 22, 2006
Corrosion protective coatings of steel pipes laid by horizontal directional drilling are particularly stressed. Thermosetting compounds based on polyurethane or epoxies have proven their performance for the protection of welded joints of such pipes. The application of thermosetting joint coatings can currently be carried out in a lamination process, resulting in glass reinforced plastics coatings, or by spatula in case of polyurethane based materials.
- the possible generation of mixing errors due to incomplete mixing.
- the possibility of creating air entrapments in the blended material due to manual stirring.
- the necessity of a multi step application to obtain coatings of some mm thickness. The necessary overcoat waiting periods extend the time for application and require to maintain a proper weathering protection of the working area.
Generally it would be possible to produce a viscosity, which allows to apply the two component compound in one step without sagging, but this would even increase the complications regarding proper mixing and air.
- the difficulty to produce an even coating thickness by manual application.This might require extra efforts to ensure the minimum coating thickness.
Casing systems are already used in pipeline construction applications, such as cement grouting of field joints for completion of the additional concrete pipe coating.
However, this principle can not directly be transferred to the corrosion protective coating of field joints, because the narrow annular gap would make it impossible to fill the casing without cavities.
Even grouting of low viscous reactive resins into a premounted casing would not completely avoid the formation of cavities, whichobviously can not be accepted in corrosion protective coatings.
The coating thickness, which can be obtained on top of the weld bead, directly results from the difference of mill coating thickness and height of the weld bead.
If this difference is smaller than approx. 3 mm (see Figure 3), a minimum coating thickness of 2.5 mm can only be obtained reliably by additional use of a spacer, which could be produced by wrapping one or more layers of a corrosion protective tape on either side of the joint area (see Figure 1b).
For that reason DENSOLID HDD is packed in two chamber cartridges, which allow both the reliable mixing via an attached static mixer and the precise filling of the annular gap between pipe and casing.
Because of its very smooth surface, the casing sheet can easily be lift off from the tack free cured coating without residues. Same as the other components, the casing sheet can therefore be reused after removal. Considering an application period of approx. | hour per joint (depending on the pipe diameter), only 5 casing sets are required for a continuous progress of work.
Currently the volume of commercially available two chamber cartridges is limited to 400 ml. To obtain a coating thickness of 5 mm, between 2 cartridges for a 4“ pipe and 14 cartridges for a 40“ pipe are thus required per welded joint.
Particularly in case of bigger diameters or long pipeline conduits  it could be desired to make available higher contents per packing unit, which would reduce costs by faster application and less packaging waste.
For this purpose and in addition to the standard size cartridges, a newly developed, pneumatically driven discharging machine (patent pending) with a working volume of approx. 6 l is available (Figure 5).
With one filling, consisting of two 2 l hose packs of resin and one 2 l hose pack of hardener, welded joints on 40“ pipes can be coated continuously without refill interrupts.
The newly developed casing system and procedure described in this report significantly simplifies the process of coating welded joints on steel pipes with two component thermosetting compounds.
The employment of such coating materials is particularly useful on pipes laid by horizontal directional drilling. Compared with standard manual application procedures, the new coating system provides various advantages, which are
- Fast working progress by one step application, regardless of the final coating thickness.
- Mixing errors or air enclosures, resulting from standard manual mixing, are
avoided by application from a two chamber cartridge with an attached static mixer.
- The uncured coating is protected against weathering and other ambient influences. By this, the efforts for protection of the working area are significantly reduced.
- The new casing system allows to produce an even coating thickness, which also and reliably ensures the required minimum coverage on top of the weld bead.
 Funk, D. "Anforderung an die Umhüllung für im Bohrpress- bzw. im Horizontal-Drilling- Verfahren verlegte Rohrleitungen", bbr, Sonderausgabe "Grabenlose Rohrleitungsbauverfahren", 2000
 Quast, M. "Neue Polyurethan-Schweißnahtbeschichtung für Horizontalbohrungen", 3R international (42), Heft 10- 11/2003, Seite 703 - 707
 DIN EN 10290 (August 2004) "Stahlrohre und -formstücke für On- und Offshoreverlegte Rohrleitungen - Umhüllung (Außenbeschichtung ) mit Polyurethan und polyurethan-modifizierten Materialien; Deutsche Fassung EN 10290:2002"
 DIN EN 10289 (August 2004) "Stahlrohre und -formstücke für On- und Offshoreverlegte Rohrleitungen - Umhüllung (Außenbeschichtung ) mit Epoxi- und epoxi-modifizierten Materialien; Deutsche Fassung EN 10289:2002"
 Fengler, E. "Umlegung einer Gashochdruckleitung durch Kreuzung des Dortmund-Ems-Kanals", bbr 1/05, Seite 35 - 37
 Lukas, A. "The practicality of drilling very long pipelines under hazardous terrain - 5 km, 10 km", Paper for IPLOCA Convention 2004, Berlin.
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Dr. rer. nat. Dipl.-Chem. Michael Quast Denso GmbH
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