Storage Tanks: A Complete Guide to Types, Materials, and Standards

From the water tower above a village to the white spheres of a gas terminal, storage tanks are the fixed points of every liquid economy. But 'storage tank' is an umbrella over wildly different engineering: what holds drinking water at atmospheric pressure shares almost nothing with what holds liquefied gas at cryogenic temperature except the word 'tank.'

Storage tanks are engineered vessels that hold liquids or gases at atmospheric, low, or high pressure, classified by position (aboveground, underground, elevated), pressure regime (atmospheric per API 650, low-pressure per API 620, pressure vessels per ASME VIII), and material (carbon steel, stainless, Glass-Fused-to-Steel, FRP, concrete). Capacities span from a few cubic meters to over 100,000 m3.

1. How Are Storage Tanks Classified?

Three independent axes define any tank — position, pressure, and construction.

· By position: Aboveground (API 650 shop- or field-welded, bolted), underground (UL 58 steel with cathodic protection, UL 1746 composite), and elevated (AWWA D100 towers and standpipes).

· By pressure: Atmospheric tanks (API 650) vent freely; low-pressure tanks (API 620) run to 15 psig; beyond that, ASME Section VIII pressure vessels and spheres take over.

· By construction: Field-welded, shop-welded, factory-coated bolted (AWWA D103-09), and panelized modular systems — each with distinct logistics and QA profiles.

· By roof and internals: Fixed cone or dome roofs, internal and external floating roofs for volatile liquids, and geodesic aluminum domes for clear-span coverage.

2. Which Material Should a Storage Tank Use?

Material selection is a matrix of stored product, chemistry, temperature, and budget.

· Carbon steel: The universal structural choice for fuel, water, and chemicals, protected by linings ranging from epoxy to GFS; highest strength per dollar.

· Stainless steel 304/316L: Food, pharmaceutical, and chloride service where an unlined metallic surface is specified; premium justified by zero coating maintenance.

· Glass-Fused-to-Steel: Bolted panels with a fired ceramic face for potable, wastewater, and digester service — 30+ year life, NSF/ANSI 61 listings, volumes to 60,000 m3.

· FRP and HDPE: Corrosion-immune nonmetallic options for small chemical and septic duties, limited in size and structural capacity.

3. Which Standards Govern Which Tank?

Codes map to service — specifying the wrong code is the most common procurement error.

· Water service: AWWA D100 (welded) and AWWA D103-09 (bolted) plus NSF/ANSI 61 for potable contact; NFPA 22 for fire reserves.

· Oil and fuel service: API 650 for atmospheric storage, API 620 for low pressure, UL 58/UL 142 for underground and aboveground fuel tanks, NFPA 30 for flammables.

· Pressure and cryogenic service: ASME Section VIII for LPG spheres and bullets; API 620 Annex Q for LNG at -162 deg C; API 2510 for LPG facilities.

· Fabrication conformity: ISO 9001/45001 management systems, EN 1090 for European structural steel, and ISO 28765 for vitreous enamel tank systems.

Data Table: Storage Tank Standards Quick Reference

Frequently Asked Questions (FAQ)

Q1: What are the main types of storage tanks?

By position: aboveground, underground, and elevated. By pressure: atmospheric (API 650), low-pressure (API 620 up to 15 psig), and pressure vessels (ASME VIII). By construction: field-welded, shop-welded, bolted factory-coated, and nonmetallic — with material options including carbon steel, stainless, Glass-Fused-to-Steel, FRP, and concrete.

Q2: What is the difference between API 650 and API 620 tanks?

API 650 governs atmospheric-pressure, flat-bottom welded storage tanks (water, fuel, crude), while API 620 covers tanks designed for internal pressures up to 15 psig, including low-temperature and cryogenic service such as LNG (Annex Q) and refrigerated anhydrous ammonia (Annex R). Above 15 psig, ASME Section VIII pressure vessels apply.

Q3: Which storage tank material lasts longest?

Properly specified Glass-Fused-to-Steel delivers 30+ years with no recoating; welded AWWA D100 steel and stainless tanks reach 40-50 years with maintenance. Longevity is duty-matched: no material wins everywhere, and lining selection matters more than base steel for corrosive contents.

Q4: How do I choose a storage tank supplier?

Verify design calculations to the governing standard (API 650, AWWA D103-09), certifications (ISO 9001, NSF/ANSI 61, EN 1090), coating system data, and delivered project references at your required scale. Leading bolted manufacturers deliver 20-60,000 m3 tanks to 100+ countries on 30-day standard schedules.