Section 43 41 13 — Welded Steel Acid Storage Tanks
MasterFormat classifies storage tanks by material, not chemical service — for concentrated sulfuric acid bulk storage, that most often means this section. The passivation finding, sizing thresholds, and the material alternatives.
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Request a Spec Review →Material Classification, Not Chemical Service
Section 43 41 13 (Welded Steel Tanks) sits under Division 43 41 00 (Storage Tanks). MasterFormat has no dedicated "acid tank" or "sulfuric acid storage" section — tanks are classified by construction material (bolted steel 43 41 11, welded steel 43 41 13, stainless steel 43 41 23, FRP 43 41 45, polyethylene). For concentrated sulfuric acid bulk storage specifically, welded carbon steel is a real, economical, industry-confirmed choice at 93-98% concentration — which is why this page anchors on 43 41 13 — but the correct section still depends on which material the project selects.
Carbon Steel Is a Legitimate Choice — With Conditions
Concentrated sulfuric acid (93-98%) forms a protective iron-sulfate film on carbon steel that substantially reduces corrosion — two independent vendors (General Industries Inc., ProTank) confirm this in their own published guidance. That means carbon steel is the standard, economical bulk-storage material at this concentration band, not a fallback. The conditions attached: keep water out (a vent with desiccant dryer), adequate corrosion allowance, good tank-bottom design, secondary containment, and a real inspection program.
Provide This to Get a Real Match Against the Section
| What to Provide | Why It Matters |
|---|---|
| Guaranteed concentration range (from the COA, not nominal %) | Commercial "98%" sulfuric acid can creep above ~98.3%, where free SO3 becomes a real material consideration for anything downstream of the tank — the tank material call itself is more forgiving, but this number still needs to be pinned down for the rest of the system. |
| Operating temperature (ambient vs. elevated) | Carbon steel's protective iron-sulfate film performs differently outside roughly ambient conditions — confirm actual operating temperature, not design-basis ambient assumption. |
| Tank size (gallons) and siting (indoor/outdoor) | ProTank flags that any tank over 4,000 gallons at 94%+ H2SO4 should go through engineering review before fabrication — not ordered off a size chart. Outdoor siting also needs the concentration-specific freezing point (93% ~-21°F vs. 98% ~30°F). |
| Corrosion allowance and inspection program | Carbon steel relies on an intact protective film — a vent with desiccant dryer (to keep moisture out), adequate corrosion allowance, and a real inspection program are conditions attached to specifying steel, not optional add-ons. |
Section 43 41 13 FAQ
Is there a dedicated CSI MasterFormat number for "concentrated acid storage tanks"?
No — MasterFormat classifies storage tanks by construction material (bolted steel, welded steel, stainless steel, FRP, polyethylene), not by chemical service. Concentrated sulfuric acid storage most commonly maps to Section 43 41 13 (Welded Steel Tanks) when carbon steel is the selected material, per this project's own vendor research confirming carbon steel as a legitimate, economical bulk-storage choice at 93-98% concentration. The chemical service and concentration are specification details applied within whichever material section is selected — Section 43 41 45 (FRP) or the polyethylene/XLPE category are the alternate material paths if a different vendor product is chosen.
Why would carbon steel be the recommended material for concentrated sulfuric acid, when it corrodes other chemicals easily?
Concentrated sulfuric acid (93-98%) forms a protective iron-sulfate film on carbon steel that substantially reduces corrosion — a real, counterintuitive passivation effect independently confirmed in two separate vendors' own published guidance. This does NOT extend to piping or pumps, where turbulent flow, velocity, and lower-concentration excursions can disturb that same protective film — see the full 93-98% Sulfuric Acid guide for the tank-vs-piping distinction.
What size tank requires engineering review before fabrication?
Per ProTank's own published guidance, any tank over 4,000 gallons at 94%+ H2SO4 should go through engineering review before fabrication, rather than being ordered directly off a standard size chart.
Are there alternatives to carbon steel for this concentration band?
Yes — a purpose-built XLPE tank with an oxidation-resistant liner (Poly Processing's system, 2.2 SG rated) is a real alternative, especially for smaller water-treatment-scale installations. However, one named vendor (ProTank) documents XLPE failing within six months of service at 98% sulfuric acid, while another (Poly Processing) lists 98% as compatible with no caveat — a real, unresolved vendor conflict. See the dedicated failure-analysis page for the full XLPE conflict before specifying that material at this concentration.
Working a 43 41 13 spec section for concentrated acid?
Send James the guaranteed concentration range, tank size, and siting — get a real material recommendation back, not a generic answer.
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