Materials selection for vapour recovery equipment is often treated as a detail left to the supplier, yet it determines how long the unit lasts in the environment it actually operates in. Two units of identical design can have very different service lives if one handles dry hydrocarbon vapour and the other handles a stream with water, chlorides or trace acids in it.
The selection question is rarely about exotic materials being better. It is about identifying which exposure in the specific stream drives the choice, and then selecting the least costly construction that handles that exposure with margin.
The exposures that drive selection
Four factors account for most of the decisions. The hydrocarbon mix, because aromatic and heavier fractions behave differently from light aliphatic vapour. Water, because it drives corrosion in some materials and encourages microbial activity in others. Temperature, because it affects both corrosion rate and mechanical properties. And trace components, because chlorides, sulphur compounds and acids in small concentrations can dominate the corrosion picture.
The reason a site-specific review matters is that these factors are not visible from the product name alone. A stream labelled by the fuel grade it derives from can contain very different trace components at different sites, particularly where blending varies seasonally.
| Exposure | Typical concern | Selection consideration |
|---|---|---|
| Hydrocarbon mix | Swelling and compatibility with seals and elastomers | Verify seal and gasket materials against the actual mix |
| Water content | Corrosion and microbial growth | Provide drainage and review wetted materials for wet service |
| Temperature | Accelerated corrosion, reduced mechanical strength | Confirm the design temperature covers upset conditions, not just normal running |
| Chlorides and other traces | Localised corrosion on some alloys | Identify trace components before specifying stainless grades |
Seals and elastomers deserve equal attention
Metal selection tends to get the attention, while seals, gaskets and flexible elements are chosen from habit. In practice, elastomer compatibility is often the limiting factor, because the seals are what actually contain the vapour at a joint, and they are sensitive to the aromatic content, the temperature and the presence of water in the stream.
The practical approach is to state the actual operating envelope when specifying: the range of products handled, the expected trace components, the operating temperature range including upset conditions, and whether liquid water can be present. A supplier given those facts can select sensibly. A supplier given a product name can only guess.
Maintenance implications of the choice
Material selection also determines what maintenance is possible. A unit built so that the critical wetted components cannot be accessed or replaced without major dismantling will be maintained less well, regardless of how good the materials are. Accessibility is part of the design, and it is worth reviewing during the selection process rather than after the first failure.
- Confirm the wetted material for every component in the vapour path, not only the main vessel.
- Check seal and gasket materials against the actual product mix and temperature range.
- Provide drains and access so wet service can be managed rather than tolerated.
- Record the materials selected and why, for the next maintenance decision.
- Review the selection if the site starts handling a different product or blend.
Documenting the selection for the future
Materials decisions are frequently made once and then forgotten, which causes difficulty years later when a unit is repaired or extended. A short record covering the wetted materials selected, the stream composition they were selected against and any trace components specifically considered turns a repair into a straightforward substitution rather than a fresh investigation.
The record has a second use. If the site later begins handling a different blend or adds a new product to the tank farm, the original selection basis is exactly what needs to be reviewed. Without it, the review starts by sampling and identifying the current stream, which is a slower and more expensive route to the same answer.
| Record item | Why it matters later |
|---|---|
| Wetted materials by component | Replacement without re-investigation |
| Stream composition and traces | Basis for reviewing a product change |
| Seal and gasket specifications | Correct spares for planned maintenance |
| Temperature envelope | Comparison against actual operating history |
Where the first repair usually reveals the gap
The first unplanned repair often concerns a component whose material was never explicitly reviewed: a gasket, a flexible connection, a small valve body or a level instrument wetted part. When it fails, the question of what to replace it with depends on the stream composition, and if that was not recorded at specification stage, the answer has to be rebuilt from samples and assumptions.
Spares planning follows the same logic. A site that holds the correct gasket and seal references can complete a repair within a shift; a site that has to identify the component first is looking at a longer interruption for what is fundamentally a small job.
| Situation | With a selection record | Without one |
|---|---|---|
| Gasket failure | Order the recorded specification | Identify material from the failed part |
| Product change proposed | Review against the recorded basis | Re-sample and re-assess |
| New tank added | Compare stream to the original envelope | Assume compatibility |
Frequently asked questions
Is stainless always the better choice?
No. Some grades are more sensitive to chloride attack than carbon steel in certain conditions. The material should be chosen against the actual stream composition rather than by general preference.
How much does trace water really matter?
Considerably, in units that see regular wet service. Water changes both corrosion behaviour and the effectiveness of condensate handling, and it should be part of the specification rather than an operational surprise.
Should materials be reviewed if the product changes?
Yes. Seals, gaskets and wetted components appropriate for one product may not suit another blend, and the review is inexpensive compared with the failure it prevents.
Luoyang Wohong Petrochemical Equipment builds three-stage vapour recovery equipment and works with operators on specification and retrofit. Send us the products and conditions your unit will see and we will help you work through the material selection.