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INDUSTRIALISATION OF INNOVATORY ELECTRON BEAM WELDING SYSTEM FOR OFFSHORE PIPELAYING [PHASE 1]

Ziel

Aim of the project is to design and manufacture a "Laboratory prototype", single gun machine, capable to demonstrate the capability of the E. B. welding process to perform butt welds for offshore pipelines to be laid in J mode. The main objectives of the proposed work are :
1. To design, manufacture, assemble and test an electron beam welding system capable of orbital welding of pipe under laboratory conditions.
2. To evaluate the latest beam power generation equipment in relation to orbital pipe welding of thick section steel.
3. To design manufacture and test inflatable seals.
4. To evaluate real-time seam tracking techniques to enable joint following under simulated industrial conditions.
5. To optimise the electron beam welding parameters and to conduct extensive tests for one pipe diameter and thickness.
The project has been completed successfully with four months of delay with respect to the working schedule. Following are the main results :
PROGRESS
The equipment was successfully designed, manufactured and commissioned. It proved possible to consistently achieve good weld quality and acceptable weld metal mechanical properties in accordance with the clients requirement for the pipe grade investigated.
Some problems were encountered with the smoothness of the orbital traverse drive but these have been largely overcome. Similarly the inflatable seal for the internal clamp caused some limitations on the pipe internal vacuum level but were sufficiently effective to maintain an adequate pressure for welding.
It is believed that previous attempts by others to apply EBW to J-pipe welding foundered because of inadequacy of the external seal and higher vacuum constraints. During the course of this work the relatively high cost inflatable seals employed by others have been replaced by a novel expandable seal. It has been produced at a fraction of the cost of the re-reinforced inflatable seal and has been demonstrated to work under laboratory conditions.
Overall much has been learned by the construction and operation of the Laboratory Prototype demonstration equipment and this can now be used to further develop equipment for the barge installation and also as a land-based welding procedure development and training system.
CONCLUSION
* A Laboratory Prototype orbital pipe EB welding equipment has been established which is capable of single pass welding speeds (with one gun) of in excess of 400 mm/min for 40 mm pipe, 1000 mm/min for 20 mm and 1500 mm/min for 10 mm thick pipe.
* The design of the chamber and gun structure is such that the pumped volume can be kept very small for a specific pipe size.
* Good progress has been made in vacuum seal design for the orbital chamber, the internal clamp and the external seal. Specifically for the external sealing a novel low cost seal membrane has been developed and a patent field.
* The principle of applying real-time seam tracking using back-scattered electron techniques has been verified.
* Welding procedures have been developed for producing high integrity welds with satisfactory mechanical properties in the particular steel chosen for the project.
FUTURE WORK
It is anticipated that this work will be followed by the design and development of a barge welding installation using all of the principles established but with components and equipment fully engineered for marine operation.
The main innovative content of this project relates to the special high power electron beam equipment and mode of operation developed by TWI. Specifically, the new technology :
a. Provides the ability to operate at reduced pressure, this minimises system down time and reduces the criticality of the vacuum seals.
b. Provides wide tolerance to parameter variations, e.g. pressure changes due to component outgassing.
c. Offers optimised electron beam shape and energy density distribution promoting good weld bead and fusion zone profile over a wide working distance range.
d. Permits operation at accelerating voltages in the range 150-200 kV, minimising the possibility of beam deflection by residual magnetism in the pipeline.
e. Includes an advanced switch mode power source leading to rapid response and ability to minimise the possibility of weld defects under adverse welding conditions.
f. Provide the ability to correctly track the centre of the weld along the welding path.
g. Providethe use of adequate inflatable seals for "reduced pressure" condition.
h. Employs a long life, indirectly heated gun cathode, increasing time between maintenance stops.
j. Utilises an advanced, rugged, RF excited, diode gun, providing overall stable performance and allowing the use of a small diameter, single core, high voltage cable.
k. This makes the gun technology ideally suitable for compact, mobile welding heads, whilst avoiding the complexity and fragility of multi-core high voltage cables, termination's and auxiliary supplies.
l. Utilise an advanced internal clamp that provide pipe alignment by means of three series of expanders, internal vacuum by means of two series of inflatable seals and a gap value at the abutted pipe ends not higher than 0.3 mm.
On land, pipelines are laid horizontally by joining standard lengths of pipe, typically using all-positional manual metal arc welding or mechanical gas shielded metal arc welding methods. In shallow waters, pipelines are laidin an S-lay configuration with the pipe lengths being joined whilst horizontal on the lay-barge. Whilst these methods are highly successful and well developed, the demand for national self-reliance in oil and gas has encouraged countries to expand offshore exploration into deeper waters where the S-lay pipelaying method cannot be employed. Of particular interest is the J-lay method where the pipe lengths are joined and laid from the barge in a vertical attitude. This method largely precludes the use of multiple welding stations and hence the electron beam process is attractive as stick section, high quality welding can be achieved at high speed in a single pass. In addition, this process is readily automated and hence has great potential to increase the rate of pipelaying by minimising welding time and the need for repairs. Saipem have decided to explore further the possibility of using the electron beam welding process for incorporation in a J-laying system.

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SAIPEM SPA
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Via Martiri di Cefalonia 67
SAN DONATO MILANESE
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