A Proved Method For J-Lay Pipeline Welding
Authors: Belloni A. 
Published: October 2008

Pipeline J lay method impose welding activity to take place in a single station. In recent years, several development have been aimed to generate a "One shot", non conventional welding system to a level of technical/commercial applicability, without a final positive result.

Saipem has developed a mechanized welding system based on GMA W process : the "Passo" system, normally used for construction of cross-country/ offshore pipelines. The system, performing reliably since 1978 has been slightly and successfully modified (the "New Passo" system) and adapted to perform as well on offshore pipelines to be laid in J-mode.

A dedicated testing program has been carried out with satisfactorily results. Welding trials have been conducted on pipe diameter 20" and 26" 0.D.(25 mm w.t.) X65 grade, simulating the J pipelaying configuration with the pipe axis inclined of 5°, 30° and 45° to the vertical. Mechanical testing (nick break, bends, hardness, Charpy and CTOD) have been conducted with positive results, in line with the requirements of the major international Standards for offshore pipeline construction (API 1104, BS 4515).

INTRODUCTION

On land, pipelines are laid horizontally by joining standard lengths of pipe, typically using all-positional manual metal arc welding (MMA) or mechanised gas shielded metal arc welding (GMAW) methods. In shallow waters, pipelines are laid in S-1ay mode, being this the configuration assumed by the pipe at the outlet of 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-/ay mode, where the pipe lengths are joined and laid from the barge in a vertical attitude. This method, due to the reduced working station size linked to the lay-barge configuration, impose welding activity to take place in a single station, with the negative effect of reducing the pipelaying productivity vs. the S-laying mode were a multistation working facility is easy to install.

Economical impact and the technological innovation associated to the new lay barge concept, are the key factors who characterise and prevent this new pipe-laying methodology to grow. Consistent investments is required for the research and development of the most important equipment involved in the laying operation and, of course, on the welding system who determine the pipelaying productivity and finally the project cost.

The utilisation of a fast and reliable welding system is therefore of primary importance. High welding speed, automation, easy operation and limited down time are essential as they have a direct influence on the overaIl production rate.

Being a "One shot" welding system not ready yet for the application, attention has to be paid to the "Conventional" systems, and more particularly to those who has proved already their validity directly in the field in the recent past. Saipem offer the "PASSO" system, modified and tested for the new application : the "New PASSO" system.