Why ASTM D-1998 Still Matters: The Standard That Separates Serious Tank Manufacturers from the Rest

When you buy an upright crosslinked polyethylene storage tank, you are buying risk management.

If the tank will hold sulfuric acid, sodium hypochlorite, fertilizer solutions, or other industrial chemicals, a failure can result in an environmental release, a downtime event, and a safety incident. ASTM D-1998 exists to reduce that risk by defining what an upright polyethylene storage tank must be, and how it must be built and tested.

What ASTM D-1998 Covers

ASTM D-1998 is ASTM International’s Standard Specification for Polyethylene Upright Storage Tanks. It applies to flat-bottom, upright, cylindrical tanks made as a one-piece seamless vessel by rotational molding. It covers tanks intended for above-ground vertical installation at atmospheric pressure, with capacities starting at 500 gallons.

ASTM D-1998 also defines service limits and calls out when you need to consult other standards for conditions outside its scope, including higher temperatures, internal pressure or vacuum, and externally imposed loads.

Type I vs Type II Tanks: The Material Choice Changes the Testing

ASTM D-1998 classifies tanks by resin type:

• Type I tanks use cross-linkable polyethylene.
• Type II tanks use non-cross-linkable polyethylene.

That classification matters because Type I tanks must meet all baseline testing requirements plus crosslink verification via gel testing.

Wall Thickness Is Engineered, Not Guessed

Section 6 of ASTM D-1998 sets a minimum wall thickness requirement using an engineering formula based on real operating conditions.

The formula uses:

• Specific gravity of the stored liquid
• Fluid head height
• Tank outside diameter
• Hydrostatic design stress of the resin at service temperature

The standard also sets a hard floor for wall thickness. The cylindrical shell cannot be thinner than 0.187 inches at any point.

If your process temperature increases, allowable stress decreases. Wall thickness must increase accordingly.

Performance Tests That Prove the Tank Was Built Correctly

A tank can look fine and still be wrong inside the wall.

ASTM D-1998 requires performance testing to assess toughness and, when applicable, verify crosslinking.

Low-Temperature Impact Test

Both Type I and Type II tanks must pass low-temperature impact testing.

Passing thresholds scale with wall thickness. For example, a specimen at 0.25 inches or less must withstand at least 90 ft-lb of impact energy. A specimen thicker than 1.00 inch must withstand 200 ft-lb.

Percent Gel Test for Type I Tanks

Type I tanks require a gel test to verify the crosslinking reaction.

A sample is exposed to boiling o-xylene to dissolve uncrosslinked material. The remaining fraction indicates the crosslinked percentage. ASTM D-1998 sets a minimum acceptable crosslink percentage of 60%.

Visual Inspection and Water Testing

ASTM D-1998 also requires visual inspection for defects such as cracks, pinholes, bubbles, crazing, and delaminations.

It also requires a water test to verify that the tank and fittings hold under hydrostatic pressure before chemical service.

Fittings, Venting, and Marking Requirements Reduce Field Problems

ASTM D-1998 extends beyond the tank shell.

It addresses fittings, including chemical compatibility and adequate venting. It also defines workmanship expectations and requires permanent marking that supports traceability, including manufacturer identification, manufacture date, capacity, design specific gravity, serial number, and tank classification.

Why “Voluntary” Still Matters

ASTM D-1998 is a voluntary consensus standard.

That means a manufacturer can sell tanks without building to this specification or performing the tests and calculations it requires. A buyer often cannot see the difference until a tank develops a leak, crack, or failure in service.

If you want an auditable baseline, ASTM D-1998 is still the best-known benchmark for upright rotomolded polyethylene tanks in chemical service.

What to Ask Before You Buy an Upright Polyethylene Tank

Ask direct questions that force a technical answer:

• Do your tanks comply with ASTM D-1998?
• Do you perform low-temperature impact testing?
• If you produce Type I tanks, do you perform percent gel testing and meet the 60% minimum?
• Can you show that your wall thickness calculation follows the ASTM D-1998 design formula?
• Will the tank marking show design-specific gravity and other required traceability information?

Poly Processing: Committed to the Standard

Poly Processing Company takes ASTM D-1998 seriously — not because it is required to, but because doing so reflects a fundamental commitment to building tanks that perform as promised. The standard is embedded into Poly Processing's quality culture. Wall thickness calculations are performed and verified. Gel tests are conducted on Type I materials with a minimum crosslinking threshold of 60%. Low-temperature impact tests are performed in-house using a twenty-pound dart. Water tests are performed at the factory by filling tanks to straight-wall capacity for at least 1 hour, and customers are strongly advised to perform a 24-hour hydrotest in the field before placing any tank into chemical service.

This level of commitment is not universal in the industry. ASTM D-1998 is a voluntary standard, and that word "voluntary" carries real implications. No federal regulation mandates that every polyethylene tank manufacturer comply with it. A manufacturer can produce and sell a polyethylene storage tank without ever referencing ASTM D-1998, without performing a single gel test or impact test, and without verifying that the wall thickness meets the engineering formula prescribed by the standard. The buyer may have no way of knowing the difference — until something goes wrong.

Addressing the "Outdated" Criticism

It is worth acknowledging that at least one manufacturer in the marketplace has dismissed ASTM D-1998 as outdated. It is true that some elements of the standard — including certain round robin testing data referenced in Section 11 — date back to the late 1980s. The standard has not kept pace with every advancement in resin technology or modeling methodology that has emerged since then, and there are thoughtful arguments to be made about areas where it could be strengthened or updated.

But here is the practical reality: ASTM D-1998 is the standard we have. It is the only published, consensus-based, nationally recognized specification for polyethylene upright storage tanks. Manufacturers who dismiss it as outdated and offer no alternative verified framework in its place are not making a technical argument — they are making a marketing argument. For buyers who want accountability and traceability in the products they purchase, ASTM D-1998 compliance remains the most meaningful benchmark available today.

If you are specifying tanks for chemical service, ask your supplier to provide proof of the claim.

If you want to talk through your chemical, temperature, specific gravity, and fitting layout, contact a Poly Processing tank specialist.