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Expansion Supports

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Expansion spool supports often create more issues than they solve.  Traditional sleepers create scour and freespan problems that often impede their operation as expansion supports.

Our custom-designed and patented product X-Matt provides an elegant solution to these problems, providing low friction supports for Z-spools and pipelines where thermal expansion can be expected.

X-Matt is a high-performance concrete mattress with a continuous HDPE surface for low friction, abrasion-free sliding.  X-Matt is based on a low profile, brick patterned mattress that stacks neatly on deck. It self-stabilises and does not promote scour.

Its ultra-low profile means free spans do not occur at the touchdown points. They also occupy minimal deck space when compared with conventional methods like sleeper supports. This reduces the cost of installation and maintenance.

X-Matt benefits: 

  • The X-Matt provides extra long (10m+) expansion support to account for installation tolerances
  • They do not require steel reinforcing over this length
  • The brick pattern provides continuous support without the pipeline catching
  • The large blocks provide excellent bearing capacity onto the sea bed
  • They stack efficiently on deck compared with sleepers
  • They are self stable and do not require scour skirts or mattress protection
  • They are low profile avoiding the spanning issues at the touch down points associated with sleepers
  • The Heavy Density Concrete mix design achieve an sg >3.0Te/m3
  • The heavy density was very stable in Internal Waves and the cyclone design condition


Optimised stacking on deck.


Subcon has deployed X-Mats on multiple projects to great success.

Their reduced vessel back deck footprint (compared to sleepers) provides significant savings to the total installed cost of the support.

While the X-Mat does not provide buckle initiation for the pipeline, it provides a sliding surface with a known friction coefficient that assists pipeline designers with buckle design and ensures the pipeline will buckle as it is intended to.

X-Mat allows designers to guarantee expansion and buckling will occur as designed and that the pipeline will not be overstressed due to burial.

X-Mat uses HDPE moulds that is part of the final product. As a solution for spool supports, there is no complex steel formwork or reinforcement bars like found in sleepers. This lends itself to being deployed in remote or low-skilled environments.

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