Steel vs. Aluminum Scuba Air Tank | Which Choose

Steel cylinders in the 12L / 232 bar class carry more gas and remain negatively buoyant throughout the dive. An aluminum AL80 (11.1L / 207 bar) is lighter, but it becomes positively buoyant near the end of the dive. If gas capacity matters most, choose steel. For casual recreational diving, aluminum is the easier option.

Buoyancy

Aluminum Cylinders

The best-known aluminum scuba cylinder is the AL80, made from 6061-T6 aluminum alloy. Its internal water volume is fixed at 11.1 liters. Empty on land, the cylinder itself weighs about 14.3 kg.

Because this alloy has a density of only 2.70 g/cm³, the walls have to be made quite thick to withstand a working pressure of 207 bar. With a wall thickness of 12.2 mm, the cylinder becomes bulkier, and its displacement rises to 15.6 liters.

The valve is typically made from C36000 brass with a chrome-plated finish. The valve itself weighs about 0.6 kg. Add the 2.15 kg of compressed air inside a full cylinder, and once the tank enters the water, it produces about 1.1 kg of downward force.

• Cylinder diameter: 184 mm
• Cylinder length: 658 mm
• Air mass when full: 2.15 kg
• Material: 6061-T6 aluminum alloy
• Thread specification: 0.750-14 NPSM
• Maximum working pressure: 3000 psi (207 bar)

As you breathe down the gas, the mass inside the cylinder decreases. At around 100 bar, the cylinder gradually reaches neutral buoyancy and no longer tends to sink or float.

Near the end of the dive, when pressure drops to 50 bar, the cylinder has already lost about 1.5 kg of air. At that point, it generates about 1.9 kg of upward pull. Although the bottom thickness is 15.7 mm, thicker than the side wall, most of the positive buoyancy acts through the middle and lower section of the tank.

That change tends to lift the diver’s hips and disturb horizontal trim. Many divers add 2 to 3 kg of lead to the weight belt specifically to counter the positive buoyancy an aluminum tank develops near the end of the dive.

Seawater has a density of 1.025 kg/L, while freshwater is 1.0 kg/L. In a lake, an aluminum cylinder produces about 0.4 kg less positive buoyancy than it does in the ocean. In freshwater, you can usually carry about 1 kg less weight, which makes things easier.

6061 aluminum alloy contains about 1.0% magnesium and 0.6% silicon. This combination gives the cylinder good resistance to large-scale corrosion in saltwater. A natural oxide layer about 10 microns thick forms on the inner wall and helps block further moisture damage.

If the cylinder is filled too quickly—more than 15 bar per minute—the wall temperature can rise to 45°C. Thermal expansion increases displacement by about 0.03 liters. Once the tank cools in the water, internal pressure can drop by around 10%.

• Magnesium content: 0.8%–1.2%
• Silicon content: 0.4%–0.8%
• Copper content: 0.15%–0.4%
• Tensile strength: 310 MPa
• Thermal conductivity: 167 W/m·K
• Density: 2.70 g/cm³

At a 5-meter safety stop, a 5 mm wetsuit expands as pressure decreases, generating about 1.5 kg of buoyancy. Add that to the 1.9 kg positive buoyancy from the aluminum cylinder, and the diver is being pulled upward with a total of 3.4 kg of force.

If you are underweighted, it becomes very easy to make an uncontrolled ascent in the final few meters. Aluminum cylinders usually have a flat-bottom boot made from high-density polyethylene. It protects the base from impacts, but it also adds a small amount of extra displacement.

Steel Cylinders

34CrMo4 chrome-moly steel has a density of 7.85 g/cm³. Because the material is so strong, the wall thickness of a steel cylinder can stay in the 4 mm to 5 mm range. Taking the HP100 as an example, its 184 mm outer diameter encloses an internal volume of 12.9 liters.

An empty HP100 weighs 15.4 kg on land. Add a 0.6 kg DIN valve, and the total becomes 16 kg. The cylinder displaces about 17.5 liters of seawater, which in water with a density of 1.025 kg/L creates 17.9 kg of buoyant force.

Subtract 17.9 kg of buoyancy from 16 kg of weight, and even an empty steel cylinder still has about 1.9 kg of negative buoyancy. Even with no gas left, it still sinks. Because of that, the diver can usually remove more than 3.5 kg of lead from the waist.

• Material: 34CrMo4 chrome-moly steel
• Working pressure: 232 bar
• Wall thickness: 4.8 mm
• Zinc coating thickness: 60 microns
• Neck thread: M25x2
• Empty weight: 15.4 kg

At 232 bar, the compressed air inside weighs 3.2 kg. Fully submerged, the tank’s total weight rises to 19.2 kg, and underwater negative buoyancy increases to about 5.1 kg. That shifts the center of ballast closer to the spine.

The center of gravity of a steel tank sits about 4 cm closer to the valve than that of an aluminum cylinder. Underwater, that gives it a naturally level trim. At 20 meters, when a 7 mm wetsuit loses around 4 kg of buoyancy, the negative buoyancy of the steel tank offsets that change very effectively.

The LP85 low-pressure steel cylinder is common in cold water. It is rated to 184 bar with an internal volume of 13 liters. Empty, it is only about -0.1 kg in buoyancy. Near the end of the dive, it feels close to neutral.

• LP85 height: 660 mm
• Empty weight: 14.1 kg
• Air mass: 2.5 kg
• Full buoyancy: -2.6 kg
• Buoyancy at 50 bar: -0.7 kg
• Diameter: 178 mm

A technical twinset made from two HP100 cylinders has a combined internal volume of 25.8 liters and can hold 5160 liters of gas. Underwater, that setup produces a steady 10 kg of negative buoyancy, which means the diver often does not need a separate weight belt at all.

A DIN connection can handle pressures above 230 bar. By comparison, the O-ring in a Yoke connection can deform by about 0.2 mm under high pressure. DIN remains gas-tight even at 300 bar.

A hydrostatic test requires the cylinder to be pressurized to 348 bar. The tank expands slightly under pressure. If permanent expansion after depressurization exceeds 10%, the cylinder must be condemned. Every test places a stretching load on the metal fibers.

Steel cylinders also solve the classic problem of the diver’s feet sinking. At a 3-meter safety stop, after the BCD is vented, the remaining 1.5 kg of negative buoyancy helps hold the diver steady in the water. That eliminates the floaty end-of-dive feeling common with aluminum tanks.

Drysuit diving is usually paired with steel tanks. Air inside a drysuit can create about 6 kg of lift. A 16 kg steel cylinder helps offset that lift, reducing the required weight belt from 8 kg to about 4 kg.

• Drysuit weighting: 4 kg (steel) vs 8 kg (aluminum)
• Wetsuit weighting: 2 kg (steel) vs 5 kg (aluminum)
• Base: rounded bottom requires a boot
• Efficiency: 15% higher

Buoyancy Comparison Table

Freshwater has a density of 1.0 kg/L, while seawater is 1.025 kg/L. In freshwater, a steel cylinder will be about 0.45 kg more negatively buoyant than it is in seawater. In lake diving, that usually lets you reduce waist weight by another 1 kg.

Durability and Corrosion

Durability and Maintenance Comparison

4130 chrome-moly steel has a Brinell hardness of around 200 to 240, which makes it highly resistant to deformation from impact. By comparison, 6061-T6 aluminum alloy has a hardness of only about 95. During dock loading or boat diving, an aluminum cylinder is far more likely to pick up scratches or dents as deep as 0.5 mm.

Because steel has a tensile strength of up to 100,000 PSI, the wall thickness of a steel cylinder usually stays between 4 mm and 5 mm. Aluminum lacks that strength, so its wall thickness has to increase to around 11 mm to 12 mm. That structural difference means that when struck by something sharp, aluminum is far more prone to visible surface displacement.

Under CGA C-6.1 standards, if a scratch on an aluminum cylinder exceeds 10% of wall thickness—about 1.2 mm—the cylinder will fail annual visual inspection (VIP). The allowable wear depth for steel is smaller, but steel is also much harder to damage in the first place.

In humid conditions, steel forms Fe鈧侽鈧?(iron oxide), which appears as loose reddish-brown scale. That rust continues to eat deeper into the metal and can create pits more than 1 mm deep in as little as a year. Once internal pitting becomes widespread, the pressure-bearing capacity of the cylinder drops quickly.

Aluminum, by contrast, forms a passive Al鈧侽鈧?(aluminum oxide) layer when exposed to oxygen. That film is only about 0.01 microns thick, but it bonds tightly to the metal surface. Even in salt spray, it blocks deeper oxidation, so corrosion on aluminum usually remains as a superficial white powder.

The rubber boot at the base of a steel cylinder is one of its maintenance weak points. Residual seawater can collect between the boot and the metal, creating a closed micro-environment. As the water evaporates, salt crystals remain, and combined with electrochemical potential differences, they can create a ring of deep rust at the bottom of the cylinder within six months.

Although aluminum handles saltwater much better, it carries the risk of SLC (sustained load cracking). After about 10,000 fill cycles, the threaded neck area can develop microscopic metal fatigue under repeated stress. This damage is not visible to the naked eye and usually requires eddy-current testing to detect.

Aluminum cylinders made after 1989 from 6061 alloy are much safer. Older 6351 alloy cylinders were more prone to neck cracking under long-term high pressure because of their microstructure and lead content. Anyone buying a used aluminum tank should verify the alloy code stamped on the shoulder.

The internal dryness of a steel cylinder has a huge effect on service life. If a fill station fails to replace filters in time and compressed air contains more than 50 mg/m³ of water vapor, visible internal rust can appear within about 3 months. Professional dive shops usually maintain a dew point below -40°C.

The hydrostatic test is the final measure of cylinder durability. Testing pressure is raised to 1.5 times working pressure. For a 300 bar steel cylinder, that means 450 bar during test. The test measures whether permanent expansion exceeds 10% of the original volume.

As long as deep oxidation does not occur, steel cylinders have extremely long fatigue lives. Some remain in service for 40 years with very low expansion rates. Aluminum, on the other hand, tends to fail hydro over time because of material creep and fatigue. Many aluminum tanks are not retired because of corrosion, but because the metal itself simply ages out.

There is an electrochemical potential difference between an aluminum cylinder and a brass valve. In saltwater, that can trigger galvanic corrosion. If oxygen-compatible lubricant is not used when installing the valve, the aluminum threads can behave like a sacrificial anode, leading to seized valves or leakage.

External coating repair is especially important for steel. A hot-dip galvanized layer provides about 80 microns of protection. If bare dark metal becomes exposed, it should be repainted immediately with a zinc-rich primer containing at least 90% zinc. On aluminum, even if all paint is worn away, exposed metal re-passivates within milliseconds and usually does not need frequent repainting.

Steel’s better heat conductivity also helps during filling. Compression heat dissipates more quickly through the steel wall, which reduces the pressure loss after cooling. An aluminum cylinder fast-filled to 200 bar in a warm environment may cool down and settle at only about 180 bar.

In terms of retained value, steel behaves more like a long-term asset. A well-maintained steel cylinder often retains around 70% of its original purchase price on the second-hand market. Aluminum has a much clearer fatigue-based retirement horizon, so once it passes 15 years of service, its real residual value drops quickly toward zero.

During long-term storage, a steel cylinder should retain at least 20 bar of residual pressure. That keeps the internal pressure above atmospheric pressure and prevents moist air from entering. Residual pressure is also recommended for aluminum, but aluminum is far less sensitive to occasional internal humidity.

For divers living in dry climates and diving mostly in freshwater lakes, steel-cylinder maintenance is relatively minor. In tropical island environments, however, aluminum’s lower-maintenance nature becomes a real advantage.

How You Should Choose

An Aluminum 80 (11.1 liters) behaves like a dynamically changing weight in the water. At 200 bar, it has about 0.73 kg of negative buoyancy. By the time residual pressure drops to 35 bar, it produces about 1.9 kg of positive buoyancy. To stay stable during the safety stop, you need about 2.6 kg of extra lead just to counter that lift.

A 12-liter high-pressure steel cylinder (HP100) behaves very differently. Full, it carries about 3.8 kg of negative buoyancy, and even when nearly empty it still remains about 0.3 kg negative. It helps keep you down for the entire dive instead of forcing you to carry extra lead to control a floating tank.

6061-T6 aluminum has a density of 2.7 g/cm³, so to withstand 207 bar its walls are usually around 12.2 mm thick. 4130 chrome-moly steel, with a density of 7.8 g/cm³, needs only about 4.8 mm wall thickness. That makes a steel cylinder 10 to 15 mm narrower in diameter than an equivalent aluminum cylinder.

Choosing steel lets you carry more gas without increasing external bulk. A 10-liter steel tank is about 50 mm shorter than an 11-liter aluminum tank. That compact size helps prevent the bottom of the tank from hitting the backs of your legs. In wrecks or caves, the narrower profile also makes movement easier.

A 300 bar steel cylinder with 12 liters of internal volume can hold about 3300 liters of gas. A normal 200 bar aluminum cylinder of similar class carries only about 2200 liters. That 1100-liter difference can give a diver with average consumption another 15 to 20 minutes at 20 meters.

DIN valves are common on steel cylinders and support 300 bar threaded high-pressure connections. Aluminum cylinders are more often paired with Yoke valves, which are usually limited to 232 bar. In a DIN system, the O-ring sits protected inside the valve body, making seal failure from impact much less likely.

Aluminum still carries the risk of SLC. Although 6061 alloy is more stable than older 6351, microscopic cracking can still develop around the neck threads after about 10,000 fill cycles. Steel has a higher elastic modulus and can tolerate the same expansion-contraction cycling safely for 40 years or more.

Saltwater is steel’s natural enemy. Once the 80–100 micron galvanized layer is damaged, bare steel begins forming red rust. Aluminum, by contrast, forms a self-healing aluminum oxide layer at scratches within milliseconds, which reduces maintenance frequency in salty tropical environments.

Iron oxide (Fe鈧侽鈧?/strong>) formed inside a steel cylinder is powdery and can flake off, potentially clogging the 20-micron filter inside a first stage regulator. The white oxidation powder formed inside an aluminum cylinder adheres more strongly and usually does not travel with the airflow into the breathing system.

The water content in the compressed air has a major effect on service life. If the compressor filters are saturated and moisture rises above 50 mg/m³, visible pitting can begin inside a steel cylinder in as little as 90 days. Professional fill stations keep moisture below 20 mg/m³ using dew point monitoring.

A new steel cylinder typically costs $450 to $600. A standard aluminum cylinder usually sells for $200 to $280. If you dive 50 times a year, steel has a lower long-term cost of ownership because it can remain in service for half a century, while many aluminum cylinders are retired after 15 to 20 years when they fail fatigue-related testing.

Hydrostatic testing is performed every 60 months. The cylinder is filled with water and pressurized to 1.5 times working pressure. If permanent expansion exceeds 10% of original volume, the cylinder must be condemned.

The temperature rise during filling also affects usable gas. Steel dissipates heat better than aluminum, so the pressure drop after cooling is smaller. An aluminum cylinder quickly filled to 200 bar can warm to 45°C, then cool in the water and settle at only 175 bar, losing about 12% of its usable gas.

Cold-water divers in 7 mm wetsuits or drysuits face major buoyancy challenges. A thick 7 mm wetsuit can add around 5 kg of lift. A 15-liter steel cylinder can provide about 4 kg of underwater negative weight, allowing you to remove two lead blocks from the belt and greatly improve trim.

Used aluminum tanks made before 1989 should be approached with caution. Many were made from 6351 alloy and require annual eddy-current testing to screen for neck cracking. Modern steel cylinders usually need only annual VIP inspection.

A rubber boot on a steel cylinder allows a 14.5 kg tank to stand upright securely. Aluminum cylinders more often have a rounded base and can tip more easily on a moving boat deck. Once they fall, the heavy cylinder body can place major shear force on the valve and damage precision components.

Divers who travel internationally year-round usually benefit more from aluminum tanks. Carrying a 15 kg steel tank through airports consumes luggage allowance far too quickly. Divers with private transport and a fixed local dive site are better served by investing in 4130 chrome-moly steel for its more precise weighting and long-term value.

Fill station limitations also matter. Many older resort compressors can reach only 225 bar. If you bring a 300 bar steel tank to one of those resorts, the actual stored gas may be reduced to only 70% of its rated capacity.

During long-term storage, a steel tank should retain 20 to 30 bar of pressure. That positive internal pressure prevents moist outside air from entering. Aluminum cylinders should also retain residual pressure, but because of their better natural corrosion resistance, they are much less vulnerable to low-pressure storage.

Size and Capacity

Wall Thickness and Dimensions

Under a working pressure of 207 bar, 6061-T6 aluminum requires a wall thickness of about 12.3 mm to distribute internal stress safely. Chrome-moly steel has a much higher yield strength, so a 237 bar high-pressure steel cylinder needs only about 4.1 mm of wall thickness. With the standard 184 mm outside diameter, that difference has a huge impact on usable internal gas volume.

An AL80 aluminum cylinder has an actual internal volume of 11.1 liters and a total length of 658 mm. By comparison, a HP100 high-pressure steel cylinder holds 12.9 liters internally while being only 610 mm long. It is 48 mm shorter, yet provides 1.8 liters more internal space and about 25% more gas.

Because aluminum is weaker, manufacturers have to make the base much thicker. The base of an AL80 often exceeds 25 mm. Steel cylinders are usually made with a cold-drawn rounded bottom, which distributes thickness more evenly. With the same displacement in the water, steel can carry more compressed gas.

• AL80 diameter: 184 mm, displacement about 15.5 liters
• HP100 diameter: 184 mm, displacement about 14.8 liters
• LP85 diameter: 178 mm, displacement about 14.1 liters
• AL40 sidemount bottle diameter: 133 mm, length 625 mm
• HP120 diameter: 184 mm, length 711 mm
• 3000 psi aluminum cylinder fill factor: 7.0 scf/L
• 3442 psi steel cylinder fill factor: 7.7 scf/L

The difference between cylinder weight and displacement determines the underwater load. An empty AL80 weighs 14.3 kg. In freshwater, its buoyancy calculation shows about 0.7 kg of negative buoyancy when full. At 35 bar, it becomes about 1.9 kg positively buoyant. The diver must carry extra lead to suppress that lift.

A HP100 weighs 15.4 kg empty. When full, it has 3.8 kg of negative buoyancy. Even at 35 bar, it remains about 0.9 kg negative. It never develops a tendency to float upward. As a result, the diver can reduce belt weight by around 2.8 kg, easing the load on the lower back.

Cylinder length also affects trim. At 658 mm, an aluminum cylinder can be awkward for divers under 170 cm tall. When kicking, the back of the head or the second stage can easily bump the valve. A 610 mm steel cylinder raises the center of gravity and places it closer to the lungs, which makes horizontal trim easier.

• Steel internal coating thickness: about 20 to 50 microns
• Aluminum oxide film thickness: about 10 to 15 microns
• Each 1 kg lead weight provides about 0.9 kg of negative buoyancy in seawater
• Steel cylinder hydro expansion limits are typically under 10%
• Aluminum burst discs are set to about 1.5 times working pressure
• Annual inspection of steel focuses especially on oxidation pits in the neck threads

Manufacturing method also sets the ceiling for capacity. Aluminum cylinders are cold-extruded, which concentrates stress near the neck. Steel cylinders are hot-spun closed, which distributes stress more evenly. That is why steel can safely handle 3442 psi or more, and why it packs more gas molecules into the same external size.

At the same breathing rate, a HP100 provides about 15 minutes more bottom time than an AL80. That comes from the extra 22.6 cubic feet of gas. At depth, where gas consumption per minute multiplies quickly, that reserve reduces ascent pressure and stress.

The standard 184 mm diameter also makes rental logistics easier. Most BCD backplate cam bands are set up for that size. If you switch to a 203 mm large steel cylinder, strap length usually needs adjusting. Most technical twinsets use steel cylinders because their slimmer profile reduces lateral drag.

Low-pressure steel cylinders (LP series) follow a different design philosophy. A LP85 works at only 2400 psi, but because its internal volume is larger, it still delivers 85 cubic feet of gas at only 165 bar. Instead of relying on very high pressure, it uses more internal space to make up the difference.

• Internal water capacity is marked as WC
• Aluminum cylinders usually list a minimum wall thickness
• Steel cylinders often list REE (rejection elastic expansion) at rated pressure
• Every 100 bar of gas consumed reduces the weight of an AL80 by about 1.3 kg
• At the same pressure, trimix compressibility differs from plain air
• A 232 bar DIN connection is more pressure-resistant than a 200 bar Yoke

Pressure and Density

The standard service pressure of an AL80 is 3000 psi, or 207 bar. Its internal water volume is 11.1 liters. At full pressure, it contains about 2297 liters of free air.

A HP100 high-pressure steel cylinder operates at 3442 psi, or 237 bar. Although its body looks compact, its true internal water volume is 12.9 liters. When full, it holds 3057 liters of air—about 33% more.

Gas does not compress perfectly linearly forever. Once you go beyond 200 bar, storage efficiency starts to deviate slightly. Because air molecules repel each other under very high compression, actual gas content at 237 bar is about 1% to 2% lower than ideal-paper calculations suggest. That margin should be included in deep-dive gas planning.

At 20 meters, surrounding pressure reaches 3 bar. Every breath uses three times as many gas molecules as it would at the surface. With an AL80, a breathing rate of 20 liters per minute at the surface becomes 60 liters per minute at depth, leaving a total endurance of less than 38 minutes.

With a HP100 at the same depth, the extra 760 liters of compressed gas buys about 12 additional minutes. At 30 meters, that reserve becomes a real buffer against current and stress. But denser gas also places a heavier demand on first-stage regulator performance.

• At 3000 psi, air density is about 254 kg/m³
• At 3442 psi, air density rises to about 291 kg/m³
• Starting from 20°C, each 1°C rise in temperature increases cylinder pressure by about 0.6%
• DIN valves are typically rated to 232 bar or 300 bar
• In Yoke systems above 232 bar, the chance of O-ring blowout rises by about 40%
• Pulling 1000 liters of gas from a 237 bar cylinder creates very high internal regulator load

High-speed fill compressors generate a lot of heat. Right after a 3000 psi fill, a cylinder may be as hot as 45°C. If you jump straight into 25°C seawater with it, cooling will pull the gauge back to about 2750 psi, effectively wasting about 8% of the fill.

Steel dissipates that heat much faster, especially when cooled in water during filling. It tends to enter the water with its true full 3442 psi still intact. Aluminum, with its 12 mm thick walls, behaves more like an insulator, so many fill operators overfill slightly to compensate for the later pressure drop.

The LP steel family behaves differently again. A LP85, filled to only 2400 psi or 164 bar, still reaches 85 cubic feet of gas. On Southeast Asian islands where old compressors struggle, that matters: low-pressure cylinders are much easier to fill fully.

• The LP85 has an internal volume of 13.8 liters, about 24% larger than an AL80
• At 2000 psi, a LP85 still carries about 1700 liters
• At the same pressure, a HP100 still carries about 1770 liters
• At weak fill stations, a low-pressure cylinder can deliver 15% more usable gas
• At 237 bar, oxygen partial pressure in air remains around 0.5 bar, still far below toxicity limits

Gas weight also matters physically. A HP100 carrying 3057 liters of air contains about 3.8 kg of gas. As you breathe it down underwater, that load gradually disappears. If you do not account for that change during weighting, the tank can start pulling you upward like a balloon on ascent.

Past 40 meters, dense gas makes breathing noticeably harder. Air molecules squeezed together rush through the second stage in highly turbulent flow. Experienced divers heading deep often prefer high-pressure steel cylinders paired with high-flow regulators to reduce carbon dioxide buildup and the sensation of breathing resistance.

Producing a 3442 psi high-pressure steel cylinder requires 34CrMo4 chrome-moly steel. Its tensile strength is roughly three times that of aluminum alloy. It can keep total expansion under 10% even under extreme internal pressure. Aluminum cylinders holding 3000 psi for years are much more prone to microscopic deformation around the neck threads.

• Every 1000 liters of air consumed adds about 1.2 kg of upward tendency to the diver
• An AL80 at 50 bar can pull upward with about 2 kg
• A HP100 at the same residual pressure still retains about 0.9 kg of downward weight
• The dense gas stored in a high-pressure steel cylinder reduces how much lead you need
• At 3442 psi, every cubic foot of air contains roughly 1.2 hundred quadrillion gas molecules

When choosing a cylinder, you also have to consider the fill station. If a dive shop fills only to 200 bar, the high-pressure advantage of a HP100 becomes largely wasted, and you are relying mostly on its extra 1.8 liters of internal volume. In that situation, a LP108 or a large aluminum cylinder may actually give better practical dive time.

Look at the shoulder stamp and find the line marked Service Pressure. If it says 3442, and you pair it with a capable regulator, you can comfortably spend an extra 10 minutes at 20 meters looking for nudibranchs.

And if you have a cylinder that has been sitting unused for a long time, never fill it blindly. Check the stamped dates. If it has gone more than 1 year without a visual inspection, or more than 5 years without a hydro test, send it to a qualified inspection facility before using it.