OFFSHORE CONSTR UCTION
Production tapered stress joint, 18m length.
A high strength low alloy steel alternative for tapered stress joints For the construction and operation of oil production facilities, it is important to find the right balance between cost and safety. Weight and strength of the material used play a role in this. Recently, Schelde Exotech had a technological first with the use of high strength low alloy steel for tapered stress joints. ALL IMAGES COURTESY OF SCHELDE EXOTECH. WORDS BY ALFRED VAN AARTSEN, MATERIAL & WELDING ENGINEER (IWE) AT SCHELDE EXOTECH.
T
apered stress joints (TSJs) are used to connect the steel catenary risers (SCRs) to bottom-fixed or floating oil production facilities. Relatively a small part, when compared to the entire length of the pipelines, especially at the deepsea facilities in the Gulf of Mexico. Because of current, waves, and movements in case of floating facilities, the forces on the TSJs can be very demanding and may lead to fatigue of the material. The damage caused by this fatigue can be very severe for the facility as well as for nature.
2 2 | O S I 2 0 2 2 | Volum e 15 | Issue 2
Schelde Exotech.indd 22
A technological first Last year, Schelde Exotech (Vlissingen, the Netherlands) constructed high strength low alloy steel TSJs for one of their clients, Subseatec. A technological first in the offshore arena. In this project, Schelde Exotech made welding qualifications, in several low alloy steel grades. After a full approval cycle, the actual production welding followed. The end-client of Subseatec will use the TSJs for connecting SCRs to a new to construct semi-submersible platform, which will be operating at a depth of approximately 2,400m in the Gulf of Mexico.
Welding qualifications started in Q1 of 2021 and involved the following low alloy steel materials: • Grade A508Gr.4 Cl.2, for forging with yield 100-120ksi (690- 827 MPa). • Grade A707Gr.3W, for forging with yield 80-100ksi (552- 690 MPa). • Grade API-5L-X65, for pipeline pup pieces, to be welded to the TSJ materials and to be connected offshore to the SCR.
Competitive alternative The A508Gr.4 Cl.2 low alloy steel, with its tensile and toughness properties, at the
o ffs h o re -i n d u s tr y. e u
07-04-2022 12:20
