ISO 21487:2022

Test Purpose and Objective

The leakage test verifies the integrity of all tank seams, welds, fittings, and connections under normal operating pressure conditions. This test ensures that the diesel tank will not leak fuel during normal service use. For diesel tanks, this is particularly important as diesel fuel has different viscosity and penetration characteristics compared to petrol.

Test Procedure

Step 1: Test Setup

• Tank must be tested with all fittings, connections, and closures installed as they would be in service
• This includes any bottom drains, side fittings, sight gauges, and inspection hatches
• Tank must be mounted or supported to prevent distortion during testing
• All openings except the test pressure connection must be sealed
• If tank has inspection hatches, ensure gaskets are properly installed and torqued

Step 2: Pressure Calculation

Calculate the required test pressure as the GREATER of:

• 20 kPa (minimum absolute value)
• 1.5 times the highest hydrostatic pressure to which the tank will be subjected in normal service
• For sealed systems: 1.5 times (maximum hydrostatic head + system relief valve pressure)

Important for Diesel Tanks: Consider tank height and any pressurized fuel systems when calculating service pressure. Diesel systems may have fuel return lines under pressure.

Step 3: Pressurization Method

• Use clean, dry air or inert gas (nitrogen recommended)
• Gradually increase pressure to the calculated test pressure
• Avoid sudden pressure application that could damage the tank
• Monitor pressure gauge continuously during pressurization

Step 4: Static Pressure Hold

• Maintain the test pressure for a minimum of 5 minutes
• Monitor pressure gauge to ensure no pressure drop or rise occurs
• Record initial and final pressure readings with timestamps
• Any pressure change indicates a leak or temperature effect

Step 5: Leak Detection

• Visual inspection: Look for bubbles using leak detection solution (soapy water) applied to all welds, seams, fittings, and connections
• Pay special attention to inspection hatch gaskets, bottom drain connections, and sight gauge fittings (specific to diesel tanks)
• Alternative methods: Ultrasonic leak detector, electronic gas detector
• DO NOT rely solely on pressure drop as the only leak detection method
• Check all threaded connections, welded joints, and gasket seals

Pass Criteria

• No visible leakage at any point during the 5-minute test period
• No pressure drop or rise during the static pressure hold period
• No bubbles or leakage detected at welds, seams, fittings, or inspection hatches
• Tank structure shows no signs of distortion or damage
• All gaskets and seals remain intact and functional

Failure Indicators

• Visible fuel or test gas leakage at any location
• Continuous pressure drop indicating a leak
• Bubbles forming at welds, seams, connections, or gaskets
• Leakage around inspection hatch, drain valves, or sight gauge connections
• Structural deformation or damage to tank

Special Considerations for Diesel Tanks

• Inspection hatches (required for diesel tanks) must be leak-tested with gaskets properly installed
• Bottom drain fittings (if present) require careful attention during leak testing
• Sight gauge connections (if fitted) must be tested with both top and bottom valves
• Side or bottom fittings with shut-off valves must be tested in operational configuration

Test Purpose and Objective

The pressure/strength test verifies that the diesel tank structure can withstand pressures significantly higher than normal operating conditions without cracking or catastrophic failure. This test ensures adequate safety margins and structural integrity. Permanent deformation is acceptable, but the tank must not crack or leak. For diesel tanks, this test is particularly important for integral tanks and tanks with bottom fittings that may experience higher pressures.

Test Method Selection

There are TWO acceptable test methods per ISO 21487:2022:

• Method 7.2.2.2 (Standard Method): Suitable for all metallic diesel tanks (both integral and non-integral)
• Method 7.2.2.3 (Alternate Method): Only for tanks meeting specific structural and welding quality requirements

Method 7.2.2.2 - Standard Pressure Test

Applicability: All metallic diesel fuel tanks (both integral and non-integral configurations)

Test Pressure Calculation:

Test pressure must be the GREATER of:

• 20 kPa (minimum absolute value)
• 1.5 times the maximum hydrostatic pressure in service
• For sealed systems: 1.5 times (maximum hydrostatic head + system relief valve pressure)

Important for Diesel Tanks: Consider maximum fuel height in the tank, especially for integral tanks. Also account for any fuel return line pressures.

Test Procedure:

• Conduct AFTER successful completion of leakage test (7.2.1)
• Tank may be partially or fully filled with water to simulate service conditions
• For integral tanks, ensure mounting simulates actual installation stresses
• Apply calculated test pressure using compressed air or inert gas
• Maintain test pressure for minimum 5 minutes
• Monitor for any cracks, ruptures, or leakage at all fittings
• Permanent deformation is acceptable

Method 7.2.2.3 - Alternate Method (Qualifying Tanks Only)

Applicability Requirements:

This method may ONLY be used if ALL the following conditions are met:

• Tank structure complies with ISO 12215-5:2019 (plating thickness, section modulus, web shear areas as for integral tanks)
• Tank structural details follow ISO 12215-6:2008 (metal construction guidelines)
• Welding quality meets minimum Class B per ISO 5817
• All welders are qualified per ISO 9606 series or equivalent recognized standards
• Complete technical drawings available showing material grades, thicknesses, dimensions, welding details
• For integral tanks: Structural calculations must demonstrate compliance with ISO 12215-5:2019

Test Pressure Calculation:

Test pressure must be the GREATER of:

• 30 kPa (minimum absolute value - note this is HIGHER than standard method)
• 1.5 times the maximum hydrostatic pressure in service + 10 kPa

Test Procedure:

• Same procedure as Method 7.2.2.2
• Apply calculated test pressure for minimum 5 minutes
• Monitor for cracks, ruptures, or leakage
• Permanent deformation is acceptable
• For integral tanks, pay special attention to hull interface areas

Pass Criteria (Both Methods)

• No cracks develop anywhere in the tank structure
• No rupture or catastrophic failure occurs
• No fuel leakage detected during or after test
• Tank maintains pressure for full 5-minute duration
• Permanent deformation is acceptable (tank does not need to return to original shape)
• Inspection hatch gaskets remain sealed (if applicable)
• Bottom fittings and drain valves show no leakage (if applicable)
• For integral tanks: No delamination or separation from hull structure

Failure Indicators

• Any crack formation in welds, seams, or base material
• Rupture or catastrophic structural failure
• Leakage of test medium at any location
• Inability to maintain test pressure for 5 minutes
• Gasket failure at inspection hatch
• Leakage at bottom drain or sight gauge connections
• For integral tanks: Separation or delamination from hull

Special Considerations for Diesel Tanks

• Integral tanks require special attention to hull-to-tank interface during testing
• Bottom fittings and drain valves (common in diesel tanks) are stress concentration points
• Inspection hatches must be tested with full gasket compression
• Consider additional test cycles if tank shows deformation near critical fittings