CYLINDER STAMPING

We have received some inquiries about the correct order of stamp marking on cylinders.

Due to a misunderstanding, the advice given has been to split the year and month with the inspectors mark.

Having checked in the latest version of the applicable standard - BS EN ISO 13769:2006 the order is given as # YY/MM - Where # is the inspector's mark and the year and month is separated by a forward slash. 

There is no need to retrieve cylinders and remark them, however inspectors should change to the format above as set out in the Standard. 
Although not required by the standard, in order to prevent confusion over the reversal of the of month and year after 2002, we continue to recommend that until 2013 that the year is stamped in full, i.e. # YYYY/MM

THREAD CHECKING M25, 3/4 - 14 NPSM

We get regular enquiries about how many turns can be allowed on a Not Go Gauge when inspecting cylinder neck and valve stem threads. The following is a reply to this question to one of our members:

The "by the book" answer is that there should be no turns allowed on a Not Go gauge (if you think about it, that's why it's called a Not Go gauge!). However, in many industries, particularly where maintenance activities are concerned, it is common to allow something for reasonable wear and tear.

In the past, the general advice given (and widely accepted) in the UK concerned only the G3/4" thread and that advice was that up to 4 turns on the Not Go gauge could be allowed on the valve, providing that the cylinder thread was good.

However, over the past 20 years or so, M25, G5/8" and 3/4" NPSM threads have become widely used additionally ASSET's membership has become Worldwide, therefore, it has been necessary to revise and rationalise this advice.

To keep matters simple, we believe a reasonable rule of thumb to be as follows: Providing the technician is satisfied that all threads are physically sound and the cylinder neck threads have been gauged and the Not Go gauge does not go then 1 (one) turn on the Not Go gauge might be allowed on the on the valve stem thread for every four good turns engaged. In effect this means approx 1T on a 200 bar Din outlet, 2T an M25 and 3T on a G3/4" and so on.
For 3/4 NPSM threads, there is further guidance in CGA 6.1 2006 as follows:

5.9 Threads and Valving.
Cylinder threads should be examined whenever the valve is removed from the cylinder. Cylinders have a specified number of full threads of proper form as required in the applicable thread standards. Cylinders shall be rejected if the required number of effective threads is materially reduced so that a gas tight seal cannot be obtained by reasonable valving methods. Thread defects include threads that are galled, worn, corroded, broken, cracked, nicked and double threaded (by forcing an incorrect valve into the threads).

This guidance should be applied with caution and is at the discretion of the individual technician who must take into account the circumstances as they present themselves.