Total has undertaken the development of electron beam welding procedures in order to adapt this high performance welding technique to offshore pipelines.
Fifteen hundred Weld runs in the horizontal-vertical position have been made up to now in order to obtain welds, corresponding to the specifications of API and according to an acceptance procedure with a view to certifying the process for pipeline welding.
For that purpose we studied the influence of all the parameters (power, focusing current, welding speed, vibration) able to modify the morphology, the soundness, tIre fitting and alignment tolerances, and the mechanical properties of the melted zone.
These tests have been performed on eleven different steels chosen in order to represent most of the steels available for pipe construction.
They demonstrated that for each considered steel there always existed a range of welding parameters leading to perfectly sound welds. They also allowed us to find up collection of 'welding parameters leadin to very wide welds (up to 6 mm) and consequently to very wide fit up and alignment tolerances.
As far as EB weld5 mechanical properties are concerned, traction, bending and HAZ Charpy V notch test have always been within the specification, on the other hand melted zone Charpy V notch values vary strongly according to the welding parameters and the chemical composition of the steels.
The investigation performed on the influence of the welding parameters as well as on the chemical com position of the steels introduced us to three ways leading to melted zone Charpy V notch values reliable beyond the specifications :
Shaping the focusing current to the power getting trough the weld,
Precise specifications for the chemical composition of the steel, in the limits of API 1104,
Use a new special filler metal.
It has demonstrated the possibility of adapting a new one station quick welding process for pipelines : the electron beam welding.
EB welding tests in the horizontal position were made to obtain welds meeting the requirements of API standara 1104 and of the specification for the fRIGG to SCOTLAND pipeline.
These tests were made on 6 steels selected so as to represent most materials now commercially available in the form of pipes for oil and gas transport.
Data 6~ the manufacturing of these pipes are given together with their chemical composition in Table 1.
Tests made on 25 and 32 mm thick pipes (steels A. B and C) showed that it was possible to obtain sound welds with very different geometries. depending on the power and on the position of the focal spot.
