Manufacturing of chemical storage tanks

A chemical storage tank looks like any other tank from the outside (a rolled shell, a head, a set of nozzles), but the design process behind it starts from a different question than a general liquid tank does. Instead of starting with volume and working outward, the first and most limiting decision is whether any candidate material will actually survive years of contact with the specific chemical involved, at its stored concentration and temperature. Everything else in the specification follows from that answer.

Compatibility drives the material choice

Corrosion in a chemical tank is rarely a simple pass/fail; it is a rate, expressed as a corrosion allowance added to the calculated minimum wall thickness so the shell still meets code at the end of its intended service life rather than only on the day it is built. For chemistries that are aggressive but still within stainless steel’s working range (many acids at moderate concentration, most alkalis, most solvents), 316L or a higher alloy is specified with a corrosion allowance sized to the specific duty. Where the chemical is outside even those alloys’ range, the choice shifts to a lined vessel: a carbon or stainless steel shell carrying a rubber, PTFE or other polymer lining that does the actual chemical resistance work, with the steel providing only structural strength and pressure containment. Lining is generally cheaper than a solid exotic alloy for very aggressive duties, but it brings its own constraints: lining integrity depends on inspection access, and a damaged lining exposes the substrate underneath, so lined vessels typically need a defined inspection interval that a solid-alloy tank does not.

Aggressive-duty examples

The chemistries that most often drive a lined or high-alloy specification are concentrated or hot acids such as sulphuric or hydrochloric acid, strong alkalis such as caustic soda at elevated temperature, and solvents that attack elastomer seals and gaskets even where they do not attack the shell material itself. In each of these cases the tank supplier works from the chemical’s concentration, temperature and any known contaminants (chlorides in particular are a common trigger for stress corrosion cracking in stainless steels that would otherwise be adequate), rather than from a generic material table, since two tanks nominally storing “the same” chemical at different concentrations or temperatures can call for entirely different materials.

Containment and spill control

Because a chemical tank failure is a safety and environmental event rather than an operational inconvenience, containment is designed alongside the tank itself, not added afterward. A bunded area sized to hold the tank’s full volume plus rainfall allowance is standard practice for any tank storing a hazardous chemical, and the bund material itself has to be compatible with the chemical it might one day hold, not just with what normally sits above it. Secondary containment logic extends to the tank’s own connections: bottom outlets on hazardous-chemical tanks are frequently avoided in favor of a top-entry dip pipe specifically so a nozzle or valve failure cannot drain the tank’s full inventory to the ground before it is noticed.

Testing before dispatch

Before a chemical storage tank leaves the fabrication shop it is proven against the same standards used for any pressure-retaining vessel: a hydrostatic or, where water contamination has to be avoided, a pneumatic pressure test to confirm the shell holds its design pressure without leakage or permanent deformation, and dye-penetrant or other non-destructive testing on welds, particularly on any weld exposed to the stored chemical, to catch surface-breaking defects a pressure test alone would not reveal.

Makfen designs and fabricates chemical storage tanks in solid stainless and lined carbon steel construction against the chemistry, temperature and containment requirements of each application, with material certificates and test records issued for every vessel.