Induction heat technology helps to provide the highest quality offshore heat treatment and pipe coating for the international gas and oil processing industries in some of the world's most challenging locations.

Two recent examples of challenging customer requirements are the Blue Stream project - a task involving the laying of a gas pipeline at record depths across the bed of the Black Sea - and BP's Thunderhorse project in the Gulf of Mexico.

The Challenges of Blue Stream

Running for some 1,250km (777mi) from start to finish and comprising a sub-marine section of two parallel 24" pipelines, this challenging contract was the result of considerable cooperation between Russia's Gazprom and Italy's Snam (ENI), and required the use of innovative technologies and the very latest state-of the-art expertise at virtually every stage of the project.

The project design contractor charged a German pipe-coating specialist with the task of providing the solutions for the girth weld coating application - a three-layer system comprising Fusion Bonded Epoxy (FBE), adhesive and a top layer of 6mm thick polypropylene.

Technical Properties
The deep-water installation involved J-lay techniques (process of continuously laying pipe at sea in deep water), and the application of the three-layer girth weld coating had to take place on a vertical pipe within the confined space available on board a lifting barge, modified for installation of large diameter pipelines at great depth. A specially developed girth weld heat and coat machine offered the technical properties and ability to provide quality and speed, as well as precise heat and coating control.

Prototype Commissioned
The prototype design began in January of 2000. The heat and coat field-joint solution needed to have the capability of applying 300 microns of FBE, and a further 100 microns of FBE/adhesive mix as demanded by the Blue Stream project. This task was completed in just 12 weeks.

Trials and Testing
Trials and testing of the heat and coat solution were carried out during the spring of 2000. The prototype was shipped for extensive testing in a work cell that had been constructed to replicate the heat and coat station aboard the on-site barge. The station included a closed cycle blaster and final layer extrusion unit. Comprehensive trials using all three elements were carried out to prove the system was capable of meeting the contractor's requirements.

Quad Rack and J-lay Solutions
A standard induction inverter delivering a maximum of 450kW at a 3kHz output frequency powered the unit. Following successful prototype trials, the production system was commissioned. The system comprised two of the 450kW, 3kHz units (one online and one backup), and a custom-built chiller system - all housed in a 6m sea container. The inverters would be located some 40m from the process unit.

At the same time, an onshore quad-rack girth weld coating system was developed. This system was used for joining 4 x 12m pipe lengths to create 48m sections prior to transportation to the on-site barge.

Significant System Advantages
The computer-controlled heat and coat machine, as used on board the on-site barge, offers the following advantages:

  • The field joint temperature profile can be accurately monitored - to give even heating along the cutback length - by preprogramming the power levels applied throughout the heat cycle. This ensures that the surface reaches the required temperature quickly - with a sharp cut off - thereby minimizing the conduction of heat along the pipe. This in turn vastly reduces the possibility of disbondment of the parent coating on either side of the cutback.
  • The application of the FBE powder takes place as soon as the surface of the pipe reaches the minimum application tempera-ture recommended by the powder manufacturer. Reduced power continues to be applied during the FBE application cycle - the FBE/ adhesive mix and the adhesive only cycle. This results in a superior bond between pipe surface and FBE layer, and a vastly improved chemical and mechanical bond between FBE and adhesive layers.
  • All process parameters can be monitored - the power applied, the time taken, the temperature reached, powder flow, etc. - so that the integrity of each coated joint is almost guaranteed.

    Thunderhorse Project Results in "Field Joint With Hang-Off Collar" Heat and Coat Solution

    The contract to provide induction heat and coat technology for BP's Thunderhorse project in the Gulf of Mexico required a solution that would not only scan, heat and coat in a vertical plane in the J-lay tower, but also treat hang-off collars located centrally on the pipe.

    Having already provided induction heat and coat technologies for the challenging Blue Stream J-lay project, the technical team set about developing a solution. One that would apply FBE, CMPP adhesive, and a final 75mm polypropylene layer to 1270mm long field joints with varying pipe diameters of 11 3/4 ", 10 3/4" and 8 5/8", and also ensure all collar faces were coated.

    The blasting, heat and coat unit for the first two layers and the third layer extruder coat were to be installed on a J-lay-capable, heavy-lifting barge. And while the number of joints - 403 to be completed on SCRs and 311 on flow lines - was technically regarded as small, BP nevertheless required coatings of the very highest quality.

    Innovative New Solution
    In considering a number of options, including a modified version of the system used on Blue Stream and a single shot heating/multi-head coatings design, the technical department decided that, in view of the field joint length, the complexities of incorporating the hang-off collar and the difficulties of working in a vertical plane, a totally new solution was required.

    Purpose-Designed Scan, Heat and Coat Technology
    It was, therefore, decided to employ scan-heating technology and combine this with a variable powder coating system to create a purpose-designed solution that would ensure the varying pipe diameters and hang-off collar faces were properly coated to the specified thicknesses. The FBE layer was specified to be in the range of 200-300 microns and a 3mm adhesive layer would follow this. The scan-heat and coat unit would apply the first two layers and the third, 75mm polypropylene layer, would then be extruded.

    Exceptionally Versatile
    After initial discussions in the spring of 2002, followed by subsequent proposals, development began in late 2003 on a highly versatile scan-heat and coat unit that would offer all the required technical properties, operate in the confined space available on the on-site barge, provide the necessary quality and speed, and deliver precise heat, functionality and controllability.

    This latest design was mounted on a hydraulic actuated robotic arm in order to provide the desired level of scanning and movement. The three elements required to complete the coating of the joint would then be sited in the J-lay tower, where space was understandably at a premium. The blaster, the scan-heat and coat unit, and the extruder would then all operate in sequence, in a confined area, with a minimum of manual interference.

    Intelligent Control
    Computer-controlled and via use of the robotic arm, the scan-heat and coat unit could be positioned over the joint in order to provide all necessary heating and coating applications.

    With three pipe diameters to contend with, some interchangeability of parts also had to be engineered into the system. For this reason, exchangeable induction coils - each gull-wing in design, integral to the coatings assembly and of lengths commensurate with the various scan-heat processes - were developed.

    Ensuring Complete Coverage
    The coating assembly was comprised of a C-frame mounted unit supporting coating heads that would oscillate by 90 degrees and tilt by 45 degrees to ensure all areas of the field joint - including the collar faces - were coated.

    With the application heads applying both FBE and adhesive powder, the scan-heat and coat unit was also designed to include extraction of all surplus powder. The operation was preprogrammed to suit the geometry of the joint, with the temperature of the surface during scanning determined by closed loop temperature control techniques.

    The design solution also included a 450kW, 3kHZ induction inverter, a remote capacitor rack, water-cooling technology, powder delivery system, twin fluidized beds and all associated controls for the operation of the scan-heat and coat unit. The company was also responsible for the supply of all operator controls for the deck-based coating stations as well as the provision of coils for weld preheating.

    Honing and Refinement
    Following comprehensive trials and testing, the newly designed scan-heat and coat system was delivered for set up and trial of each of the various elements required, including a simulated robotic arm, so that the coating process could be honed and refined prior to installation on the on-site barge.

    The Future of Scan-Heat Technology for Line-Pipe Field Joint Coating

    Committed to a policy of continued innovation, new scan-heat coat solutions are being developed that will change the way FBE anticorrosion coatings are applied in the J-lay, S-lay and Spool-Bay environments. Building on proven technology, the latest development scheduled for launch in early 2007 is being expressly developed to reduce powder wastage and improve operator health and safety by preventing FBE powder from entering the environment where coatings are applied. IH

    For more information contact: Radyne, Molly Millars Lane, Wokingham, Berkshire RG41 2PX; Tel: + 44 (0) 118 978 3333; Fax: + 44 (0) 118 977 1729; E-mail:;