Hatch Cover Ultrasonic Tightness Testing: Leaks Located Before the Cargo Gets Wet

Why hatch cover weathertightness matters

The hatch covers of a bulk carrier or general cargo ship close the largest openings in its weather deck, and the Load Line Convention requires them to be weathertight. In service that depends on a long run of rubber packing pressed evenly against steel compression bars, at the coamings and at every cross joint between panels. Packing ages, compression bars wear and bend, covers sag and cleats are left loose, and the result is water in the hold that nobody notices until the cargo comes out.

The cargoes that suffer most are those worth most when dry: grain, soya and rice that cake, sprout or heat; steel coils, plate and wire rod that rust; paper reels and pulp that receivers reject outright; and fertilisers and cement that set or degrade. Charterers and shippers of these cargoes often make a tightness test a condition of loading, and P&I clubs have long encouraged owners to test before loading rather than defend a wet-damage claim afterwards. A cover that leaks badly in heavy weather is a safety concern as well, not only a cargo one.

Ultrasonic test, hose test and chalk test compared

Three tests are in common use, and they answer different questions. A hose test sprays water at the joints from outside while someone inside the hold watches for it coming through; it is simple and visual, but it needs an empty hold, cannot be used with water-sensitive cargo aboard or in freezing weather, and a jet that misses a defect or does not reach every joint gives a false pass. IACS Recommendation No. 14 sets out the conditions under which a hose test should be carried out. A chalk test marks the compression bars with chalk and closes and reopens the cover to see whether the packing picked up a continuous line; it shows contact, not compression or tightness.

The ultrasonic test is the only one of the three that produces a measured reading at a known position, indicates compression as well as leakage, and can be carried out with cargo already in the hold. It does not replace looking at the covers: drain channels, non-return valves and the structure of the panels still need a visual examination, and no test can show that the crew will secure the covers properly at the next port.

Defects commonly behind a failed test

Packing is the usual culprit. Rubber that has been compressed for years takes a permanent set and no longer springs back to fill the gap, sections are crushed where a cover has been landed off line, and lengths go missing or are joined badly after repairs. Packing painted over with the rest of the cover loses its elasticity. Renewing packing piecemeal with a different profile or hardness from the original leaves steps at the joins, and steps leak.

Steel faults are harder to see and take longer to put right, which is why their exact position matters. A wasted or bent compression bar, a distorted coaming top plate or worn bearing pads change the height at which the packing meets the bar, so the same cover can be over-compressed at one corner and open at the next. Cross-joint wedges and locators wear until the panels no longer pull together, and on folding covers the hinges and their pins do the same. Cleats over-tightened to stop a leak crush the packing nearby and often move the leak somewhere else.

Drainage is the last line of defence. Drain channels blocked with cargo residue or scale, and non-return valves that are seized, damaged or missing, let water that passes the outer seal into the hold or let sea water run back in through the drain. A joint can pass the test while the drains are what flood the hold, so they are looked at on every job.

Class-credited testing and the IACS UR Z17 rule

IACS UR Z17, the procedural requirements for service suppliers, lists firms engaged in tightness testing of closing appliances such as hatches and doors with ultrasonic equipment among the service suppliers a classification society must approve before it relies on their results. When an ultrasonic test is carried out for a class survey, the society therefore expects a firm it has approved for that service, and its surveyor decides how the result is used.

Atlantis NDT is not approved by any classification society for this service. We are preparing for UR Z17 audits with DNV, Lloyd's Register and ABS; no certificate has been issued, and until one is issued that covers ultrasonic tightness testing, class-credited testing needs a firm approved by the ship's class society. Our tests serve the owner's and charterer's own decisions: pre-loading checks, on-hire and off-hire surveys, repair verification and checks between surveys, none of which needs class approval. Tell us the ship's class and the reason for the test when you enquire, so the scope and the report are set for the right purpose.

If a charterer, a P&I club or a class rule asks for operators certified under a particular scheme, include it in the enquiry and we will confirm what applies before the job is booked.

Doors, access hatches and container ship covers

The same method applies to other closing appliances whose seals depend on compressed packing: weathertight doors in the superstructure and deckhouses, small access hatches on deck and in the forecastle, and the closing devices of ventilators. These are tested with the transmitter on the inner side and the receiver run around the frame, and the defects follow the same pattern of aged packing, distorted frames and worn dogs or cleats.

Container ships need care. Many have pontoon covers designed with gaps between panels and labyrinth seals rather than full weathertight packing, so the test plan follows the ship's design arrangement and does not treat a designed gap as a defect. On ships with fully gasketed covers, the test runs as it does on a bulk carrier.

Frequently asked questions