When a plant needs a tank for acid, caustic, brine or process water, the shortlist usually comes down to two options: coated steel and rotomoulded crosslinked polyethylene. Both work. They fail in completely different ways, and that difference is what should drive the decision.
How each one fails
Steel fails from the inside. A coating is only as good as its continuity, and the places it loses continuity are predictable: welds, nozzle penetrations, supports, and anywhere the tank was cut or drilled on site. Once the barrier is breached, corrosion starts in a spot nobody can see, and by the time it shows on the outside the wall has already lost thickness.
Rotomoulded XLPE fails from the outside, and slowly. The material is homogeneous through the wall – there is no coating to chip and no liner to delaminate. What limits service life is environmental stress cracking under chemical exposure, UV degradation if the tank sits outdoors unstabilised, and mechanical damage. All three are manageable with grade selection and installation practice.
Where XLPE clearly wins
- Corrosive service. A wide range of acids, bases and salt solutions are handled without a barrier layer, so there is no single point of coating failure.
- Seamless construction. No weld seams means no preferential corrosion path and no radiographic inspection to schedule.
- Installation weight. A polyethylene tank can often be set with lighter lifting equipment and simpler foundations than an equivalent steel vessel.
- Cost at moderate size. For atmospheric tanks in the few-hundred to few-thousand litre range, tooling and fabrication economics usually favour rotomoulding.
Where steel still wins
Be honest about the limits. Steel takes pressure, high temperature and large volumes far better than rotomoulded polyethylene. Above roughly 60-70 degrees C, or where the vessel must be pressure-rated, or where the tank is measured in tens of cubic metres, a steel or lined steel design is usually the correct answer. Structural supports and agitator loads also favour steel.
Specification points that decide the outcome
Most field failures in XLPE tanks trace back to one of four decisions made at the quotation stage, not to the material itself:
- Grade choice. A general rotomoulding grade is not automatically a chemical tank grade. Crosslinking level, density and comonomer type decide stress crack resistance.
- Wall thickness. Uniform wall is worth more than a thick nominal wall. Specify minimum wall at the base knuckle, not average.
- UV stabilisation. Outdoor installations need it specified, not assumed.
- Fittings and penetrations. Every nozzle is a stress riser. Flange design and reinforcement matter more than the tank body in many failures.
One more practical point: chemical compatibility should be checked against the actual concentration and temperature of service, not against a generic chart at room temperature. Concentration and temperature both change the answer.
Choosing between them
If the duty is atmospheric, corrosive, moderate temperature and moderate volume, rotomoulded XLPE is usually the lower-risk choice over the whole life cycle. If the duty involves pressure, heat or very large volume, steel is the right tool and no amount of grade selection changes that.
Review our rotomoulding grades or talk to us about a specific duty.
