"Ready" is a design basis, not a label
Storage described as hydrogen- or ammonia-ready is only ready if the design basis says so. A conventional atmospheric product tank cannot be converted to either service by re-certification. The governing code changes, the material specification changes, the containment philosophy changes, and the process safety case changes.
The practical question for an owner planning an energy-transition terminal is therefore narrower and more useful: which decisions must be taken now, at concept and FEED stage, because they cannot be reversed later without rebuilding.
Refrigerated ammonia: the near-term case
Ammonia is the carrier the market is actually building. It liquefies at atmospheric pressure at approximately minus 33 °C, it has an established global trade and an existing fleet, and it can be used directly as a fuel or feedstock or cracked back to hydrogen.
Governing standards. Large refrigerated ammonia tanks are normally designed to API 620 with the applicable low-temperature annex, with API 625 governing the tank system as a whole, that is the combination of primary container, secondary container, insulation, foundation heating and instrumentation. Additional national and regional standards apply by jurisdiction. The applicable set is fixed by jurisdiction and by the Employer's specification, and should be settled in the design basis before layout work begins.
Containment philosophy. API 625 distinguishes single, double and full containment systems. The choice is not primarily an engineering preference; it is a consequence of the site's separation distances, the population and asset exposure downwind, and the regulator's expectations. Ammonia is toxic, and dispersion modelling of a credible release will often drive the containment decision and the plot layout together. Deciding containment late is expensive, because it changes the tank system, the bund and the plot plan at once.
Materials. At ammonia storage temperature the primary container is generally fine-grain low-temperature carbon steel with impact testing at the design metal temperature, not the 9% nickel steel used for LNG service at approximately minus 165 °C. Specifying LNG-grade material for ammonia service is a real and avoidable cost error.
Stress corrosion cracking. Ammonia can cause stress corrosion cracking in carbon steel, particularly where oxygen is present. Mitigation is well established and is addressed through design, fabrication and operating controls together. It is a design and operating requirement, not an inspection afterthought, and it belongs in the design basis and the operating manual together.
Boil-off. Heat ingress generates boil-off gas continuously. The tank does not stand alone: it requires a boil-off gas compressor and reliquefaction package, or a defined disposal route, sized to the calculated heat leak plus flash on receipt. Insulation performance, tank geometry and boil-off handling are one coupled problem. A tank designed without its boil-off system is not a design.
Foundation heating. A refrigerated tank on grade requires a foundation heating system to prevent frost heave. It is a small item that fails badly.
Hydrogen: a different problem entirely
Hydrogen is not stored in atmospheric tankage. It is stored either as a compressed gas in pressure vessels or, at approximately minus 253 °C, as a cryogenic liquid in vacuum-insulated systems. Both sit outside the atmospheric tank codes, and both are pressure-equipment problems governed by the applicable pressure vessel and piping codes, with NFPA 2 and the equivalent jurisdictional codes governing separation distances and safety.
Three characteristics drive the design.
Embrittlement. Hydrogen can degrade the mechanical properties of certain steels. Material selection, hardness limits and welding procedure qualification are containment integrity issues, not documentation issues.
Small molecule, low ignition energy. Leak-tightness requirements, joint selection and detection philosophy are tighter than for hydrocarbons. Flanged joints tend to be minimised in favour of welded construction.
Ortho-para conversion. In liquid hydrogen the slow conversion between the two spin isomers releases heat inside the tank and drives boil-off beyond simple heat ingress. Catalytic conversion during liquefaction is standard practice and is a factor in any storage duration study.
The consequence for terminal planning is that hydrogen storage at scale is a process facility, not a tank farm. Where an owner's requirement is bulk energy storage and export, ammonia is usually the practical answer and hydrogen the exception.
Ammonia as a hydrogen carrier
Because ammonia is easier to liquefy, store and ship than hydrogen, most announced export projects convert hydrogen to ammonia for transport and either use the ammonia directly or crack it back at the point of use. That is why hydrogen and ammonia infrastructure is planned together rather than as alternatives.
For the storage designer, the consequence is that the ammonia tank is rarely a standalone scope. It sits between a synthesis or import facility and either a jetty, a cracker or a consuming plant, and its capacity, turnover rate and boil-off duty are set by the rest of the chain. Sizing an ammonia tank without the ship size, the loading rate and the downstream offtake profile produces a number, not a design.
What "ready" should mean at FEED stage
Where an owner wants optionality, the decisions that must be taken early are limited and identifiable:
- Plot and separation. Toxic and cryogenic services need distances that cannot be recovered on a congested site. Reserve them at layout stage.
- Containment philosophy. Fix single, double or full containment before the bund and the plot plan are frozen.
- Marine and transfer interface. Ship size, loading arm rating, and transfer line design govern tank capacity and turnover.
- Boil-off and disposal route. Defined at FEED, not deferred to detailed engineering.
- Utilities and power. Refrigeration duty is a continuous load with reliability implications.
- Regulatory route. Ammonia is a toxic substance under most major-hazard regimes. The consenting timeline frequently governs the project schedule.
Retrofitting any of the first three is a rebuild.
Chemie-Tech's position
Chemie-Tech’s storage experience includes Tankage Packages I to III at the Dangote Refinery and Petrochemical complex, comprising 154 tanks with an aggregate capacity of 36.8 million bbl and a maximum diameter of 92 m, on the 50-tank T1 and T2 tank farm package at the Basrah Refinery Upgrading project, and on terminal EPC delivery across Africa, the Middle East, Europe, South Asia and Oceania.
On the energy-transition side, Chemie-Tech has provided pre-development and FEED support for a green hydrogen and ammonia project in Abu Dhabi covering feasibility, site selection, technology evaluation and execution planning. That is the stage at which the decisions listed above are made, and the stage at which most of the cost of the eventual facility is fixed.
The consistent finding is that energy-transition storage projects fail at concept stage, not at construction stage. They fail because a plot was fixed before the containment philosophy was chosen, or a capacity was fixed before the offtake profile was known.
Common Questions
Can an existing product tank be converted to ammonia service?
Not as a code matter. The governing standard, material specification, insulation, foundation heating and containment system differ from atmospheric hydrocarbon service. Conversion is a rebuild.
Why is ammonia stored refrigerated rather than pressurised?
At scale, refrigerated storage at near-atmospheric pressure is more economical than pressurised storage. Pressurised storage remains normal for small volumes.
What usually governs the schedule on an ammonia terminal?
Consenting and long-lead procurement rather than construction. Ammonia falls under major-hazard regimes in most jurisdictions, and the safety case and permitting route should be started in parallel with FEED.
How early does containment philosophy have to be fixed?
Before the plot plan is frozen. It determines separation distances, bund arrangement and the tank system itself, and it cannot be changed later without redesigning all three.