Under Pressure

A practical exam to finish the course

It was time to start putting everything we learnt during the course together. We each worked through a scenario where we were performing a Periodic Inspection and Test (PIAT) on an old aluminium cylinder. First was the recording of information from the cylinder:

  • Make
  • Serial number
  • Specification
  • Working and testing pressures (PS and PT)
  • Volume
  • Manufacturing date

I then judged the external condition of the cylinder as Good, Satisfactory, Poor or Rejected. Obviously, had it been rejected I would have stopped at this point; the next stage would be to Condemn it and then Render Unserviceable.

Having confirmed the cylinder was empty, I removed and assessed the valve using the following criteria:

  • Valve body condition
  • Valve action
  • Outlet thread condition (or condition of the A-Clamp)
  • Stem thread condition

Both threads were tested with a Go Gauge and a Not Go Gauge and then I decided whether I needed to replace or refurbish the valve. With everything looking good I moved on the the cylinder. I visually checked the cylinder thread and confirmed it was longer than 27mm. After checking the cylinder neck thread with the Go Gauge and Not Go Gauge I confirmed the cylinder and valve threads matched and recorded they were both G¾.

I used an ultrasonic thickness meter to confirm the wall thickness was greater than the Minimum Design Wall Thickness. As this was an old cylinder (Aluminium AA6351), it required an Eddy Current Test to check for cracks in the neck. This was performed with a VisualPlus tester and no cracks were found.

Now it was time for the hydrostatic test using an Octopus Test Systems jacket system. The cylinder passed the test, was emptied, dried with steam and left to cool. The total (TE) and permanent expansions (PE) were recorded and the calculation run to confirm the PE was less than 5% of the TE.

Once the cylinder had cooled, the valve was refitted. Then it was a matter of stamping the cylinder with the test date and affixing the next PI date sticker.

This was the end of the DITC course and I managed to achieve 95% in the homework/final exam. The course was very enjoyable with a good mix between classroom and workshop sessions. I am very proud to be an ASSET qualified Technician.