Question

With reference to air receivers and bottles explain with reasons:

(a) Why regular systematic internal inspection is advisable. (4)

(b) Which internal areas of large receivers should receive particularly close examination? (4)

(c) How bottles are inspected internally and what parts should be closely examined? (4)

(d) How the condition of a bottle or receiver that cannot be inspected internally is checked. (4)

Answer 1

(a) Regular internal inspection of air bottle:

The bottles should be inspected every year and the mountings to be overhauled every two years.
The reservoirs should be carefully examined for corrosion and pitting.
Corrosion and pitting usually occur on the bottom of the reservoir, around the valve openings and in the way of any cooler areas.
If the air reservoir is adjacent to the shipside, which is often cooler than the other parts of the engine room, corrosion or pitting can be expected on the inside cold surface of the reservoir adjacent to the shipside.
The corrosion and pitting are associated with vapour coming out of suspension from the compressed air pumped into the reservoir.
The moisture forms on the bottom and cold surfaces and causes corrosion.
Oil particles may also be carried over with the compressed air from the compressor, and if oxidation of the oil occurs this may also lead to corrosion and pitting.
A further internal examination is to be conducted for: pitting corrosion, fatigue cracking, laminations, indentations and localised bulging

(c) Parts to be inspected.

The air bottle is fitted with stop, safety and drain valves and a manhole door at one end.
Reservoirs are inspected regularly; precautions must be taken against internal corrosion and pitting, especially at the top and bottom end. (Bottom where condensate accumulates)
It is of great importance that the reservoir should always be well-drained and that a protection coating should be applied.
All valves should be thoroughly maintained, and inspection should be carried out on these valves for air tightness, corrosion, erosion, and soundness of valve spindle and springs (hammer test) should be inspected.
Manhole door joint face, door studs and nuts, and radial clearance between door and frame (1/16" in diameter) must be checked for corrosion and erosion.

(d) Test for air bottle if cannot enter.

Large pressure vessels, which can perform internal and external inspection, do not need to perform hydraulic pressure tests if the visual condition is good and no defect.
If the pressure vessel cannot enter and cannot perform internal inspection must be hydraulically tested.
The test pressure is 1.25 x working pressure and is maintained for 10 minutes.

How pressure test carried out.

To pressure test the air bottle the hydraulic pressure is 1.25 x working pressure should be maintained for 10 minutes in accordance with the requirements of the classification societies concerned, during which the surveyor should carry out a thorough examination for any defects. A special pressure gauge known to be accurate is used when the receiver is undergoing the hydraulic test.
The receiver will have to be sealed, wire brushed internally and thoroughly cleaned out in preparation for the test. Cleaning the unit internally must not be done by the use of toxic or inflammable agents.
The valve chest will be removed and a plate having a screwed hole in the centre will be joined up. The receiver is filled with water until water shows at the air vent to ensure that no air is trapped inside.
One end of the high-pressure flexible pipe will be screwed into the screwed hole of the plate and the other end of the pipe will be attached to the discharge side of the hydraulic hand pump. The hand pump will now be started and the pressure gradually brought up to the stated amount.

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