Offshore hydrogen storage system made of UHPC concrete

Standard concrete can suffer various problems due to hydrogen, especially in special applications such as
hydrogen storage or hydrogen pipelines. The main problems are:

1. Micro-cracking due to hydrogen pressure

• Problem: hydrogen is a small molecule that can enter pores and micro-cracks in concrete. When hydrogen is under high pressure in these pores, it can expand the pores and enlarge cracks.
  
• Consequences:
  
• weakening of the mechanical strength of the concrete.
  
• Progressive damage due to cyclic loading.

Due to its very high density, UHPC has significantly fewer problems with this issue and its consequences.

 

2. Damage due to hydrogen embrittlement (indirect)

• Problem: Hydrogen does not chemically attack concrete, but it can embrittle steel reinforcement elements embedded in the concrete. This is referred to as hydrogen embrittlement.
  
• Consequences:
  
• Reduction in load-bearing capacity due to cracking and failure of the reinforcement steel.
  
• Shortening of the service life of the concrete structure.
  

Due to the very high material density, possible hydrogen embrittlement occurs after aconsiderably longer period of time and to a small extent. 

 

3. Reaction with free ions and moisture

• Problem: Hydrogen can react with moisture and chemical compounds in the concrete (e.g. calcium hydroxide), creating by-products such as water or hydroxide ions.
  
• Consequences:
  
• Alteration of the chemical composition of the concrete, which can lead to a reduction in alkalinity.
  
• Accelerated corrosion of the reinforcement due to the loss of the passivation effect.

Occurs to a much lesser extent in UHPC

4. Pore structure and permeability

• Problem: Hydrogen can easily diffuse through the pore structure of concrete due to its small molecular size, especially in porous or poorly compacted concrete.
  
• Consequences:
  
• Loss of tightness, which is critical for hydrogen storage tanks or pipes.
  
• The ingress of hydrogen causes pressure build-up and damage.

Hydrogen can only penetrate UHPC concrete very slowly and under high pressure because UHPC concrete is an extremely dense material.

5. Increased risk of a hydrogen fire

• Problem: If hydrogen escapes from the concrete (e.g. through diffusion or crack formation), there is a risk of a hydrogen fire, as hydrogen is highly flammable.
  
• Consequences:
  
• Safety risk for the surrounding area.
  
• Additional thermal stress on the concrete.

Due to its high material density and strength, the risk is only present to a very limited extent
with UHPC concrete.

Ultra-high performance concrete offers many advantages, but requires careful planning and adaptation when exposed to hydrogen, especially in demanding applications such as hydrogen storage or transport lines.

UHPC Construction test for the deep sea use

Research in deep sea construction

For more than a year, we participated in a research project of a German university. It was about the exploration of future concrete constructions for the deep sea.

For a few weeks, the result is available. The UHPC Binder material manufactured by us passed the tests by far from other binder materials.
The reasearch team of the university did models made of different concrete materials The models have been tested for corrosion, leaks and pressure resistance. The compressive strength should be so high that the concrete construction can withstand a sea pressure of 3500 m /2.17 mi permanently.

 

At the end of the long-term test, there were no cracks or other damage to the UHPC concrete construction.

 

Research in deep-sea energy storage
Another interesting research project is the construction of compressed air storage balls for the deep sea. The first concrete ball was manufactured in Germany by the Hochtief company and successfully tested as part of a research program. A very good standard concrete quality was used, but it reaches its material limits with a diameter of over 3 m.

One problem that still needs to be solved is the limited transportability of such hollow spheres due to their diameter.
For commercial use, the diameter must be larger. This means that the hollow spheres have to be manufactured on site, which is very costly, or the hollow sphere is manufactured from several prefabricated UHPC concrete elements, similar to the tower elements in wind power plants.

UHPC Offshore grouting could be an interesting alternative solution to this standard concrete here.

Why?

UHPC has a very high compressive strengt of over 200 MPa / 29000 psi
UHPC has been used in the offshore sector for more than 30 years.
UHPC is absolutely resistant to salt water
UHPC is easy to pump and is self-compacting
UHPC constructions can withstand much greate external and internal pressure loads than standard concrete. Due to the enormous compressive strength, the necessary wall thicknesses can be reduce  depending on type of construction
UHPC is waterproof from 10 mm thickness. Steel reinforcement is much more corrosion-proof in UHPC than in concrete
UHPC has an extremely low to no pore volume.
As far as the heat development during pressure build-up is concerned, the standard version of UHPC is temperature resistant up to 450°C. In the high temperature version, UHPC is permanent temperature resistant up to over 1000°C / 1832°F.