Ole Gjerstad

SubseaDesign, Equinor, Subsea 7

Groundbreaking connection system

SubseaDesign’s SeAlign connection system is continuously making a larger footprint in the subsea market. With the most recent contracts awarded for multiple Equinor projects, the size range is rapidly expanding. After a busy coming year, filled with design and qualification activities, the portfolio will cover up to 36”.

Ole Gjerstad

SubseaDesign, Equinor, Subsea 7

6” SeAlign connector during cyclic sliding test

The SeAlign connection system was developed and patented over 10 years ago. Over the years, prototypes were manufactured and tested, with a few actual deliveries. The product’s breakthrough came in 2016 when SubseaDesign was awarded the diver misalignment flange scope for Johan Sverdrup Phase 1 by Statoil. More than 50 connections were delivered in sizes 8”, 14” and 18”.  Tie-in was completed before summer this year, with very positive feedback from Equinor and the team from Subsea7. Key words used were ease of operation, safe and effective diving.

Made-up SeAlign flanges on Johan Sverdrup


Divers making up an 18” SeAlign flange on Johan Sverdrup

What is a sealign?
The SeAlign system provides a leak-tight connection with hub misalignment up to 3 degrees in all directions. In effect, it is a ball joint between two intersecting pipes which is locked at make-up. Misalignment flanges for topside and diver connections have been around for many years. The unique thing with SeAlign is the robust hub profile which directs loads away from the sealing areas. Spherical surfaces in the hubs ensure correct energizing of the seal for all misalignment angles, at a low proportion of the preload. This ensures that seal compression and leak tightness is not affected when pressure and external loads are applied to the connection. Also, the bolt tension remains stable, making the connector very robust against fatigue.

SeAlign is available in two primary versions:

  • SeAlign with manually (diver) operated swiveling clamp rings and stud bolts
  • SeAlign with ROV operated clamp (3-segmented, single drive screw)


Cross section of diver operated SeAlign misalignment connector

Why misalignent? 
Bjørn Pettersen, former Technical Manager of SubseaDesign says with a smile: Some potential clients have told me "we don't need to have misalignment". All subsea connector specifications assume that pipes are bent into alignment by large structures and/or high capacity tools. From my perspective, it is always beneficial to not spend large efforts aligning pipes when you don’t need to. Any plumber will agree to this.

There will always be misalignment due to measurement and fabrication tolerances. While traditional connection systems start off with typically 40-50% utilization of the pipe only from aligning the hubs during make-up, a SeAlign connector is made up without tie-in bending moments. The benefit of SeAlign can be applied in different ways:

  • make the spools shorter and smaller
  • maintain spool lengths and give reduced operational loads
  • relaxed fabrication tolerances (e.g. for short, rigid modules that will require special fabrication jigs)

With shorter spools, significant financial savings can be realized by reduced installation cost:

  • Increased weather window as shorter spools allow installation in higher sea state
  • Reduced crane, rigging and vessel requirements
  • Smaller vessel or more spools on same vessel
  • Reduced overall risk of the operation

Also, for flexible jumper applications, the misalignment capability may be exploited by having a downwards inclined outboard hub, and thereby reducing the free span length.

Other techincal advantages
For manually (diver) operated SeAlign connections, the tolerance to stud bolt pretension is wide. This means the flanges can be made up using torque tools as an alternative to tensioning tools, which may be required for other flange types. This gives significant savings as valuable vessel and diving time can be reduced to a minimum.

After make-up, movement of the hubs from bending moments is arrested by friction. The hub profiles provide an end stop should a operational bending moment initiate rotation and try to increase the misalignment beyond 3 degrees. With this capability, the SeAlign connection may behave as a safety joint in case of accidental loads exceeding the frictional capacity. Once at end stop, the connectors are designed to have capacity exceeding the pipe while maintaining leak tightness. So far, no operational load cases exceeding the frictional bending capacity have been identified during rigid spool design on any of SubseaDesign’s connector delivery projects.

For some applications, movement of the hubs could also be intentionally designed into the system, e.g. a PLET experiencing significant movement from thermal expansion of a large bore pipeline. To support such uses, SubseaDesign have performed tests demonstrating that a SeAlign connection remained leak-tight after 500 cycles from 0° to 3° and back again, with full design pressure applied to the bore for the whole duration of the test.

New projects
This summer, SubseaDesign was awarded a contract by Equinor for the supply of diver operated SeAlign connectors to several ongoing pipeline modification projects. The delivery scope includes both 32” and 36”, whereof 32” will be qualified the coming months. Managing Director Eivind Rasten says: - We are very pleased with the confidence Equinor shows in us by placing this contract with a very strict delivery schedule.  The positive experiences from Johan Sverdrup Phase 1 have confirmed the capabilities of the SeAlign product and SubseaDesign as a connector supplier.

SubseaDesign are also supplying ROV operated SeAlign connections for the Equinor Bauge manifold project. The delivery includes complete tie-in systems for 6” and 10” flexible jumpers. Some of this equipment is already subsea after PLET and riser base installation this summer.

Installation of 10” Bauge PLET/PLR (TechnipFMC) with SeAlign connector

Lastly, this spring 20 off 10” and 2 off 20” ROV-operated connectors for rigid spools were supplied to a project in Russia. This marks an important milestone as the first significant international delivery of the SeAlign product.