Overview

Sodium hypochlorite (NaClO) — industrial bleach — is the workhorse disinfectant in municipal drinking water, wastewater, and food-processing CIP systems. The commercial concentrate is 10% to 15% by weight, higher than household bleach (3% to 6%). Unlike most corrosive chemistries, the biggest tank-failure mode for hypo is NOT corrosion but UV-accelerated decomposition that releases oxygen and chlorine gas, pressurizing the tank headspace and degrading the resin from the inside out.

Why Concentration Limit Is 16.5%

Snyder's chart caps hypochlorite service at <16.5% active chlorine. Above that, the decomposition rate becomes unmanageable for polyethylene tanks — the OEM simply will not warranty higher concentrations. In practice commercial 12.5% concentrate sits well below this ceiling, which is why it is the industry standard. If you are sourcing 15% hypo, verify it stays below 16.5% after thermal cycling and long storage (it drifts up as water evaporates).

Gasket: Viton, Not EPDM

Unlike caustic, hypochlorite attacks EPDM. Viton (FKM) is required for all wetted gaskets — manway, bulkhead fittings, flanged connections. Hypo also attacks most plasticizers used in off-the-shelf hose gaskets, so specify Viton all the way from storage tank through dosing system.

Bolt Material: Titanium

Snyder's bolt spec for hypochlorite is Titanium, not Hastelloy or 316SS. Chloride decomposition products attack 316 stainless rapidly (pitting within months) and Hastelloy more slowly but still noticeably. Titanium is the industrial standard for hypo service; budget accordingly.

Venting Is Non-Negotiable

Hypochlorite off-gasses oxygen and chlorine under UV exposure and during normal thermal cycling. An undersized or blocked vent will pressurize the tank, stress the sidewalls, and eventually burst a seam or manway. Specify a screened vent sized per the Chlorine Institute guidelines — 2" vent per 1000 gallons is a common rule of thumb but verify against your site's temperature swing and fill/draw schedule.

System-of-Construction Table (Snyder Industries)

This is the exact specification Snyder Industries publishes for this chemistry. Every column is required — changing any of them voids the service rating.

Frequently Asked Questions

Can I use a standard HDLPE tank for 12.5% hypo?

For INDOOR service, yes — a 1.9 ASTM HDLPE tank with Viton gaskets, PVC fittings, and Titanium bolts. For OUTDOOR (UV-exposed) service, no — you need the resin #880059 formulation or an insulated/covered tank. Ordering a generic HDLPE tank for outdoor hypo is the single most common field mistake.

Why does my hypo tank smell like chlorine?

Some off-gassing is normal during fills and on hot days. Heavy chlorine odor around the vent indicates either undersized venting, elevated tank temperature, or hypo concentration drifting above spec. Measure the actual concentration; ventilate the area; confirm vent is not blocked.

How often do I need to replace Viton gaskets?

Viton in hypochlorite service typically lasts 3-5 years between replacements, shorter in outdoor or heated installations. Inspect at each scheduled tank cleaning; replace if rebound is visibly reduced.

Is 316SS ever acceptable on a hypo system?

For dry-side hardware and structural elements that never contact the liquid or fumes, 316SS is adequate. For any wetted or vapor-exposed hardware, Titanium is required. Do not mix alloys on the same tank — galvanic couples in a chlorinated environment accelerate pitting on the less-noble metal.

Source Citations

• Snyder Industries — Chemical Resistance Recommendations (current edition)
• Enduraplas / Equistar Technical Tip — Chemical Resistance of Polyethylene (12-page reference)

Chemical-Service Tanks

These HDPE vertical chemical-storage tanks from Snyder Industries ship pre-engineered for industrial chemistry service at 1.9 ASTM design specific gravity. When you order for sodium hypochlorite (bleach) service, our team verifies the full materials-of-construction stack (resin grade, fittings, gaskets, bolts) against the OEM recommendations above before shipment — no surprises at commissioning.

120 Gallon

120 Gallon HDPE Vertical Chemical Storage Tank

SII-5700100N45

$738.78

550 Gallon

550 Gallon HDPE Vertical Chemical Storage Tank

SII-1820000N45

$1,158.00

1,100 Gallon

1100 Gallon HDPE Vertical Chemical Storage Tank

SII-1830000N45

$2,468.99

1,500 Gallon

1500 Gallon HDPE Vertical Chemical Storage Tank

SII-8120100N45

$2,047.00

2,500 Gallon

2500 Gallon HDPE Vertical Chemical Storage Tank

SII-5090000N39

$3,352.00

5,500 Gallon

5500 Gallon HDPE Vertical Chemical Storage Tank

SII-7000000N43

$10,975.00