Into the ocean they go!

The seas tie the world together. That is why the unseen arteries of our energy system run across those waters. Steel pipelines carry the fuel that keep factories humming – and homes warm. But the sea is vast, deep and unpredictable, with an ecosystem and rules of its own. Not just nature itself, but how we, humans operate within it too (think trawling nets, electrical-/data cables). Pipelines have to cope with that reality – and stay put on the seabed.

So… just add weight?

Under water, a pipeline displaces water – and buoyancy pushes back. Rule of thumb: 1 m³ of water ≈ 1,000 kg of lift. The combined mass of steel and concrete must comfortably outweigh that, tuned to each diameter, wall thickness and steel grade. This isn’t “just add more”; it’s exact calculation for controlled negative buoyancy. (In practice, a 12-metre joint often lands between 15 and 40 tons.)

No ordinary concrete

Standard ready-mix won’t do. For undersea use, the industry blends cement with iron ore. That makes the mix roughly 1.5 times heavier than conventional concrete, often with a faint rusty hue from the ore. Mass alone isn’t enough though; the jacket has to be tough. So we reinforce it to prevent loss of integrity under impact or during handling.

Two ways to reinforce

• Wrapped reinforcement (wire mesh): the pipe rotates; we wrap the mesh, when we apply the concrete mix.
• Pre-welded cages: slide a welded cage over the pipe first, then apply the concrete jacket.

The right choice depends on mechanical requirements, line design and overall project cost.

Two ways to apply the jacket

There are also two application methods:

• Wrapping / compression: a controlled, quasi-continuous process with a more paste-like mix. The pipe turns gently; the finish is clean and repeatable: an ideal process for smaller pipe diameters at high capacity production outputs.
• Impingement: a dry, slightly moist mix, projected at high speed onto the pipe. High throughput and excellent adhesion – the option when higher density (and weight) is required and bigger diameters production leads.
  Together with clients we specify, per route, the best combination of reinforcement, recipe and application. The outcome: the exact target submerged weight, tight diameter/weight tolerances and minimal material use.

What happens above water (and why it matters below)

Before a single meter goes offshore, everything is staged in the storage yard. On the lay barge, joints are welded on board and placed on the seabed. These are floating factories with serious day rates—downtime isn’t an option. We plan to the lay window (for example, the Baltic roughly March–October) and align recipe, QA/QC (Quality Assurance/ Quality Control, handling and logistics early with the yard and contractor. In good conditions you lay 2–4 km per day. Predictability here is pure cost control.

Aren’t we ‘moving off gas’?

Renewables are the future every country is working toward. But the fact remains: no nation can yet do without gas. We still rely on oil and gas to drive, to heat our homes, and to keep industries running. Even in the most progressive countries, alternatives aren’t yet sufficient—whether because of infrastructure, cost, or sheer scale. The transition is happening, but not overnight.

The renewable-energy routes are already there

The upside: the same corridors remain usable for decades—also for other energy carriers. A well-made concrete-weight-coated line is designed for at least 60 years; in practice, a hundred isn’t unusual.

So what flows next?

Offshore wind can be converted into hydrogen and brought ashore via existing or new routes. Captured CO₂ can be transported safely to depleted fields beneath the seabed. Win-win when you think about it.

Would you like to brainstorm with us?

Want to talk concrete weight coating? We’re happy to spar, test and deliver what works on your line, within your window. Our engineers know the pitfalls and will go as deep as needed (even close to 3,000 metres). Have a look at our full product description: https://www.selmers.com/selmers-solutions/concrete-weight-coating-plant-cwc/