Concrete mattresses and subsea protection

SPS pioneered concrete flexi-mats in the North Sea in the 1990s. From Great Yarmouth it now designs, casts and loads out protection for pipelines, cables and foundations around the world.

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Head office +44 (0)1493 600700

A ship’s crane at Great Yarmouth lifting a yellow SPS lifting frame with a load of concrete mattresses slung beneath it
Mafumeira Sud, offshore Angola. SPS designed mattresses and lifting equipment for Saipem on the Chevron-led project and mobilised 1,800 tonnes of cargo through Great Yarmouth’s deep-water harbour.

Projects for Saipem, Subsea 7, Technip, Boskalis, VolkerStevin, Bibby Offshore and Bohlen & Doyen

Protection and stabilisation products

A standard range, or units designed to your specification, each engineered for lifting, impact, future recovery, settlement and stability.

Grout, sand & gravel bags 25 kg to 1.5 t, ROV-release and drop bags
Special products Stabilisation weights, weight collars and gravity anchors
Artificial reef units New habitat for marine life
Loc-Bloc & onshore range Free-standing, dry-bonded walls, stocked at Great Yarmouth and Dundee

Units designed to your drawings

From a 28-tonne headwall to 12-metre crossing supports, cast to your drawings or designed with you.

Talk to an engineer

Speedloaders: several mattresses in one lift

Vessel time is among the biggest costs offshore. SPS Speedloaders save up to 80% of vessel loading time by lifting several mattresses at once.

  • Speedloaders lift five 6 × 3 × 0.15 m mattresses, or three 6 × 3 × 0.3 m, in a single lift
  • Rated 25 Te SWL, designed to DNV standards, certified for offshore use and ideal for wet-storing mattresses
  • Hydraulic release frames operated by diver, ROV or from the deck
Ask about Speedloader hire
A barge loaded with strapped stacks of SPS concrete mattresses alongside a tug at sea
An SPS Speedloader lifting a stack of tapered concrete mattresses at the quayside
SPS Speedloader: several mattresses, one lift
150 fleximats loaded five at a time, in an 8-hour load-out Cladhan
900+ mattresses recovered in batches, some wet-stored for 6+ months Hess FFFA decommissioning
100 t hydraulic frame designed by SPS to place 500 unique mattresses Tay Road Bridge

Speedloader lift count

Enter your load-out to compare single lifts with Speedloader lifts, using SPS’s rated capacities.

Mattress size
Single lifts 180
Speedloader lifts 36
Crane time saved 24 hrs 144 fewer lifts (80% less)
Quote Speedloader hire for this

Indicative only, using SPS Speedloader capacity for 6 × 3 m mattresses. Crane cycle time, sea state and vessel change the result.

Six seabed threats, and the SPS protection for each

Choose a threat to see what it does, the SPS products that answer it and a project where they were used.

Cross-section of a subsea asset and the SPS protection that stops the selected threatTrawl boardSection A–A, not to scale
The problem

Scour: the seabed washing away

When current meets a pipeline, a monopile or a bridge pier, it accelerates around it and strips the sediment away. It can be gradual or rapid, but it’s cumulative, and it ends in unsupported spans and undermined structures.

The SPS answer

Buoyant fronds slow the water like seaweed, so sediment settles instead of scouring. Rock filter units and mattresses armour the bed outright.

Proven on Dudgeon OWF: 250 rock filter units for the scour protection of two 42 km export cables, loaded out from the SPS quayside in Great Yarmouth.

Get a scour protection quote
The problem

Dropped objects: impact from above

Anchors, tools and cargo dropped from vessels and platforms can dent, puncture or rupture a subsea line.

The SPS answer

SPS protection covers take the impact without transferring load to the pipeline, umbilical or structure beneath. Concrete mattresses add a flexible protective layer, and SPS has put its fleximats through dropped-object testing on film.

See the test: Dropped-object test on SPS concrete fleximats

Get a dropped-object protection quote
The problem

Trawl gear: snagging and impact

Trawl boards and fishing gear dragged across the seabed can snag exposed pipelines and cables, damaging the asset and the gear.

The SPS answer

Tapered (wedged) fleximats have enlarged, tapered edge elements that give the line an overtrawlable profile, so gear rides over instead of snagging. Once installed, fleximats can scour into the seabed for even more stability. For hard points, SPS covers are designed for trawl-board impact.

Proven on Cygnus: 70 wedged concrete fleximats with artificial fronds for Bibby Offshore, loaded with SPS Speedloaders to cut vessel lifts and port time.

Get an overtrawlable protection quote
The problem

Instability: uplift, drift and buoyancy

Extreme currents and waves, buoyancy forces or a lost weight coat can lift or shift a pipeline off its design route, and soft soils may not support it at all.

The SPS answer

Log mats use reinforced concrete logs for a greater overall density than a fleximat, adding weight exactly where it’s needed, and can form a foundation on soft soils. Stabilisation weights, weight collars and gravity anchors cover the rest.

Proven on Lianzi: 40 log mattresses covered with anti-abrasion pads for Subsea 7, with purpose-made SPS lifting equipment for a safe, quick installation.

Get a stabilisation quote
The problem

Crossings: new over existing

Every new pipeline or cable that crosses an existing one needs guaranteed separation, a stable bearing surface and supports that won’t settle or slide.

The SPS answer

SPS pipeline supports and crossing bridges are engineered around seabed conditions, settlement and footprint, pipelay tolerances, the bearing surface (low-friction, high-friction or low-impact) and design life, and come with full documentation and certification.

Proven on Kizomba Satellites: complex 12-metre crossing supports designed and manufactured by SPS for Saipem, offshore Angola.

Get a crossing support quote
The problem

Erosion: banks, coasts and defences

Rivers, tides and storms undercut embankments, harbour walls, breakwaters and sea defences, and the toe is usually where the damage starts.

The SPS answer

Revetment mattresses are flexible fleximats that follow the embankment profile, so protection holds as the profile varies. Rock filter units armour the toe, and Loc-Bloc walls go up quickly with no special foundations.

Proven on the Ipswich Tidal Barrier: 75 concrete mattresses stabilising the River Orwell bed during construction of a flood defence protecting 1,500 residential and 400 commercial properties.

Get an erosion control quote

Projects from the North Sea to the Gulf of Mexico

Selected SPS projects in offshore wind, oil and gas, marine civils and decommissioning.

What the project teams said

Their flexible and adaptable approach to work has been of real benefit on this project. Not only is it good to work with a UK company, but it is useful that they are conveniently situated near to a port, making transportation of goods that much easier.

Rene Fischer, Project Manager, Bohlen & DoyenKentish Flats Extension offshore wind farm

The mattress speedloaders hired from SPS and used on our project allowed us to mobilise 180 mattresses in less than 5 hours due to their multi-mattress lift capability. This kept port calls to less than 12 hours, ensuring the vessel could leave at the first available high water, saving the project several vessel days. I’d use them again in a heartbeat when executing a large scale mattress installation campaign.

Lead EngineerWestermost Rough offshore wind farm

Six manufacturing sites, from Great Yarmouth to Batam

Headquartered in Great Yarmouth, SPS casts at the site that suits your mobilisation, or at a mobile facility set up for the job, including some of the most inaccessible locations in the world.

World map showing SPS manufacturing sites in the UK, Qatar, Mexico, Malaysia and Indonesia, an office in Singapore, licensed manufacture in the United States and selected project locations Great Yarmouth Dundee Ras Laffan Ciudad del Carmen Johor Bahru and Batam USA, under licence
  • Manufacturing site
  • Office
  • Licensed manufacture
  • Selected projects

Manufactured in, or supplied to, Europe, Africa, North, Central and South America, the Middle East and Asia.

  • Great Yarmouth, England Head office, manufacturing and quayside load-out
  • Dundee, Scotland Manufacturing
  • Ras Laffan, Qatar Manufacturing, with Subsea Protection Systems LLC in Doha
  • Ciudad del Carmen, Mexico Manufacturing through the SSProcar-SPS joint venture, since 2012
  • Johor Bahru, Malaysia & Batam, Indonesia Manufacturing
  • Singapore Subsea Protection Systems (Far East)
  • United States SPS mattress designs manufactured under licence
Two SPS engineers reviewing drawings at a desk
Design and engineering
A curved timber mould for a precast concrete unit in the SPS factory
Purpose-made moulds
A night-time load-out on a floodlit vessel deck
Load-out at night
Since the 1990s
SPS pioneered concrete flexi-mats in the North Sea, then widened the range and the handling kit.
A permanent workforce
SPS keeps a permanent workforce to retain skills, led by a management team with over 150 combined years in offshore energy.
Engineered to standard
Products are engineered to the appropriate international standards, with safety factors for lifting offshore.

Quality, health, safety and the environment

SPS quality assurance processes conform to ISO 9001 and are independently tested and verified. If results and safety ever conflict, SPS staff choose safety, with the board’s support.

QMS ISO 9001 Registered
FPAL Registered, empowered by Achilles
Achilles

“The safety and well-being of our employees and sub-contractors is non-negotiable. No employee or sub-contractor will be expected, directed or encouraged to submit themselves or others to any uncontrolled risk in order to satisfy a work-related requirement.”

Fred Rogers, Chairman, in the SPS company statement

Test films and datasheets

A dropped-object test on SPS fleximats, an SPS concrete mattress and a 50-tonne frame in operation, from the SPS YouTube channel. More on YouTube

Dropped-object test on SPS concrete fleximats
SPS concrete mattress
50-tonne frame in operation

Common questions

What is a concrete mattress?

A concrete mattress is a flexible blanket of cast concrete blocks linked by UV-stabilised polypropylene rope. Laid over a pipeline, cable or umbilical, it protects against dropped objects and trawl gear, adds weight for stability, prevents scour and separates crossing assets. SPS mattresses can also act as supports or foundations, and control riverbank erosion.

What sizes are available?

SPS manufactures a standard range: 6 × 3 m mattresses at 0.15 m and 0.3 m thick are common, alongside longer units such as 12-metre fleximats. Standard concrete density is 2.3–2.5 t/m³, and we can supply heavier or lighter mixes, special profiles and protection pads to suit your design.

Can mattresses be recovered at the end of a field’s life?

Future recovery is one of SPS’s standard design criteria. On the Fife, Flora, Fergus and Angus decommissioning campaign, SPS Speedloaders were used to recover more than 900 mattresses in batches, and SPS’s Dundee facility hosted trials of URS’s UTROV mattress recovery tool.

Which standards and accreditations do you work to?

SPS’s quality management system is ISO 9001 registered and independently verified, and the company is FPAL registered through Achilles. Products are engineered to the appropriate international technical standards. Speedloaders, for example, are designed to DNV standards and rated to 25 Te SWL, with full documentation and certification.

Request a quote

Send quantities and drawings, or describe the asset, the seabed and the programme. Drawings can go to enquiries@sps-gb.com or with the form.

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