Portable Tank Rejection at the Filling Terminal
A shipper presents a portable tank for filling with UN 1830, Sulfuric acid, Class 8, PG II. The tank is a UN portable tank with a capacity of 21,000 litres. The inspection certificate shows a hydraulic test 30 months ago and a periodic inspection 5 years ago. The tank's markings include the UN number, the proper shipping name, and the capacity, but the maximum allowable working pressure marking is corroded and illegible. The tank shell shows a shallow dent near a support, and the bottom outlet valve has a worn gasket. The shipper wants to load because "the certificate is still valid." The receiving vessel sails in 48 hours.
1. Evaluate the tank against the portable tank requirements and decide whether filling should proceed.
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Filling should not proceed until the defects are resolved.
- Test and inspection dates: a 30-month-old hydraulic test and a 5-year-old periodic inspection may or may not be within the interval required for this tank type and substance. The applicable portable tank instruction for the entry must be checked; the interval depends on the tank code and the product. The shipper's assertion that "the certificate is still valid" is not sufficient without matching the dates to the required interval.
- Markings: the maximum allowable working pressure marking is illegible. Required markings must be legible; a corroded MAWP marking means the tank cannot be verified against its design and must be re-marked by an authorized facility.
- Structural condition: a dent near a support is a potential stress concentration and must be assessed, not ignored. It may require repair or rejection depending on depth and location.
- Bottom outlet valve: a worn gasket on the outlet of a sulfuric acid tank is a leak path for a highly corrosive liquid. The valve must be serviced before filling.
Decision: reject for filling, quarantine the tank, and require re-marking, assessment of the dent, valve service, and confirmation that test dates meet the required interval.
2. Explain how the properties of sulfuric acid specifically affect the tank selection and valve concerns.
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Sulfuric acid, Class 8, PG II, is strongly corrosive and attacks many materials; it also generates heat on dilution and can evolve hazardous fumes. The tank must be of a type and material approved for this substance under its portable tank instruction, and the gaskets and linings must be compatible. A worn gasket is not a minor item: it is the most likely point of failure and must be of a material resistant to the acid.
The bottom outlet valve is a particular concern because it is the lowest point and the most exposed to leakage and impact. The Code requires protection of bottom outlets for tanks carrying corrosive substances, often by a protective housing or by design that shields the valve. The inspection should confirm that protection is intact.
The dent near the support matters because acid plus a stress concentration plus vibration in service is a corrosion-fatigue risk. The tank should be assessed by a competent person before it carries acid again.
3. What documentation and records should accompany the tank, and what should the terminal tell the shipper?
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Records and documents:
- The transport document showing UN 1830, SULFURIC ACID, 8, II, with the number and kind of packages and total quantity.
- The portable tank inspection and test certificate, with dates that satisfy the required interval for the tank instruction.
- Confirmation of the tank code and that it is authorized for this substance.
- The container/vehicle packing certificate if the tank is carried in a unit, and emergency response information.
What to tell the shipper: the tank is rejected for filling pending re-marking of the MAWP, assessment and any repair of the dent, replacement of the outlet valve gasket, and verification that the hydraulic and periodic inspection dates meet the required interval. The 48-hour sailing is not a basis for loading a tank with an illegible pressure marking and a leaking valve on a corrosive service. Offer to prioritize the inspection so the shipment can move once the tank is compliant, and record the rejection in the terminal's system.