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.