Concrete pit for liquid sulphur storage 2

[RogerH]

A have a question related to concrete pits used for liquid sulphur storage (wihtin oil refineries). Since the 50-60's liquid sulphur has been collected in concrete fabricated pits. The liquid sulphur is about 140-150 °C. Usually after 20 years or so cracks in the concrete starts to be a problem, since oil and water in the ground leaks into the pit (when the level of sulphur is below the crack(s). In some areas of the world, the ground water is more salty/brackish and these salts contaminate the product (sulphur). I assume that hot,concentraded salt also can contribute to the degradation of the concrete, anybody that has any information on this?

I have been informed that manufacturers today have improved the concrete quality and technique of fabricating these pits. So that one should have a substantially longer life of these concrete pits today. Can anybody in this forum enlighten me on the subject and/or perhaps give

http://www links

to a site that can provide me more information on the subject.
Thanks

 

[dbuzz]

Sulphite liquor does cause degradation in concrete. The sulphates react with the tricalcium aluminate in the cement to form calcium sulphoaluminate, which has a larger volume that the original material. This volume change results in the formation of cracks in the concrete which leads to spalling. Resistance to sulphate attack is improved by the use of sulphate-resistant cement or the partial substitution of cement with fly ash and/or the use of dense concrete (from using a low water:cement ratio).

Waterproof polyethylene membranes on the surfaces of the pit walls and floor that are in contact with the soil should prevent ingress of water and contaminants. There are also admixtures, such as Cementaid’s Everdure Caltite, which purport to produce impermeable concrete by virtue of hydrophobic and pore-filling ingredients.

Protective coatings for concrete have advanced considerably since the 1950s. While I haven’t dealt with sulphite liquor before, I would anticipate, for a hot process liquor in an industrial plant, some sort of protective coating on the wetted surfaces of the pit floor and walls.

 

[RogerH]

dbuzz
Thanks for your reply
I dont know if the sulphatation is applicable here since the pit contains liquid (yellow,elemental) sulphur. Some oxidation could occur but normally the 'contaminant' is in the sulphide form, e.g. disulphides, H2S and polysulphides.
However what I have seen from older pits 15-25 years old, is that they develop cracks and whatever that is on the outside in the ground water comes into the pit (when the liquid sulphur level is low).
If the cracks is dependent on thermal aging, cycling, or corrosion I cannot judge. The main issue today is if the quality of concrete is improved so that the lifetime expectancy of a new pit is such that it will be a lot higher than the older ones, i.e. 15-25 years.
Any information on the subject is welcome

 

[JGrubb]

Roger -

there are a number of causes of concrete deterioration primarily:

alkali-silica reaction
freeze-thaw damage
corrosion of reinforcing bars
sulfate attack
physical forces (abrasion, impact, etc)

Because you are asking about sulfur pits, as concrete engineers the first thing that comes to mind is sulphate attack. however, to really know the cause of the cracking an investigation is necessary. There can be many contributing factors including the environment, mix design, age, and loading.

Unless the cause of the cracking is known, it is hard to design a more durable concrete pit. If the cause is known, new pits can be designed using products and methods that have been developed. But your question on whether "quality of concrete is improved" is far too inspecific to be answerable.

 

[boo1]

T Lock is what was used for protection at the
Hyperion Intermediate Pumping Station. Check out

http://www.leewens.com/plastic_liners.htm.

 

[tena010]

I agree with jGrubb. You have to do some field research on the causes for the cracking. After 20 yrs of service, quite probably it could be a fatigue in the material, however the problem could have started years before. About new concrete technology, now you can get better strenghts, qualities and high performance in concrete than you used to get 20 yrs ago, but probably you'll need a better design detailing since that has improved too. In my experience, tanks and pits have proved to be kind of tricky for the unexperienced structural engineer.