Periodic inspection of dissolved acetylene cylinders under IS 8433:2017: what is checked when, and what condemns a cylinder

A dissolved acetylene cylinder is the one gas cylinder that cannot be pressure-tested in service. Its porous mass is cast into the shell and stays there for the cylinder's life, so the periodic inspection that Indian law requires is a different exercise from the hydrostatic retest of an oxygen or nitrogen cylinder. IS 8433:2017, drawn from ISO 10462:2013, sets out what is examined instead: the mass, the neck, the valve and the outside of the shell, with numerical limits for each.

The foreword to IS 8433:2017 states that, because of the porous mass, neither a hydraulic nor a pneumatic pressure test, nor a visual inspection of the internal surface of the shell, can be carried out. IS 8868:1988 cl 2.1 says the same in a note: dissolved acetylene cylinders are not hydrostatically tested at periodical inspection. The hydrostatic stretch test is done before the mass is cast, normally at manufacture (ISO 10462:2013 cl 6.4 also requires a hydraulic test at the stamped test pressure before new porous material is introduced into a shell whose test interval has lapsed), at not less than 60 kgf/cm² or 53 kgf/cm² with a fusible plug, with permanent stretch limited to 7.5 % of the total (Gas Cylinders Rules 2016 Rule 37(vii)). That test is covered on hydrostatic stretch testing; the cylinder testing and retest page sets DA cylinders against the other gases.

The consequence is that everything the inspector can learn about the shell comes from its outside, and everything about the mass comes from what can be seen or felt through the valve opening.

Two instruments set the timing, and they agree:

IS 8433 refers the interval itself to IS 15975, and Rule 35(1) refers the period for all cylinders to the same standard. The two-year and one-year figures above are from Rule 39(2) and IS 8868. For comparison, CGA C-13 in the United States requalifies the shell every 10 years and the porous mass once, at 20 years from manufacture. India therefore inspects a monolithic-mass cylinder five times in the period in which the US inspects the shell once. Note that IS 8433:2017 still cites the Gas Cylinder Rules 2004, which Rule 73 of the 2016 Rules repealed; the 2016 Rules govern.

The cylinder is emptied to atmospheric pressure, allowed to warm to ambient, and its pressure and weight are recorded. Before the valve is removed, if a blocked valve is suspected, IS 8433 cl 5.3 requires an inert gas to be introduced at a pressure lower than 5 bar and its discharge observed; a valve that will not pass gas is treated as obstructed and dealt with under a controlled procedure. AIGA 022/26 warns that rapid blow-down cools the cylinder and gives a false "empty" indication, after which gas is released as it warms, so the cylinder must be normalised to atmospheric pressure before the valve comes off.

Once the valve is out, IS 8433 cl 5.4 requires all neck filters and felts to be rejected. Fine carbon powder on them may indicate a flashback into the cylinder, and all such cylinders are rejected.

IS 8433 cl 6.1 requires external visual inspection for dents, cuts, gouges, bulges, cracks, laminations and loss of material from the base; heat, torch or arc damage; corrosion, with special attention to the base, the shell-to-footring junction and the neck-ring junction; illegible or unauthorised stampings; and the integrity of permanent attachments. Damaged valve guards, neck rings and footrings may be repaired or replaced, but no welding or heat may be applied to the pressure-containing part. Annex B gives the limits:

On fire damage, IS 8433's table rejects cylinders showing partial melting or distortion and allows those with only charred paint or a damaged guard, date ring or plug to be considered after inspection. Rule 24(2) of the Gas Cylinders Rules 2016 is stricter and governs: dissolved acetylene cylinders damaged by fire shall be condemned and destroyed. Rule 12(5) adds that no repair may be made to a DA cylinder showing a leak in its weld seam.

Fusible plugs and other relief devices are examined for damage and, where damaged, replaced and checked for gas tightness (cl 6.5); plugs are never peened or repaired. Valves are inspected and maintained under cl 6.6 and Annex E, with threads checked for diameter, form, length and taper, lubricants and elastomers compatible with acetone and acetylene per IS/ISO 11114-2, and internal and external leak checks at operating pressure after reassembly as IS 3224 requires. The cylinder-to-valve threads and neck ring are examined under cl 6.7; a neck ring is changed only by an approved procedure. At reassembly (cl 6.8) new filters are fitted so that the base of the valve stem contacts them, and a ring indicating the year of the next inspection is fitted over the valve stem where regulations require. The valve page and fusible plug page give the component requirements.

A cylinder that passes is marked with the inspection date and the symbol of the inspection body or test station, and the next inspection year is shown by a ring between the valve and the cylinder. For monolithic masses, stamping on the shoulder of a welded cylinder is not permitted unless a data plate or the manufacturing specification provides for it. The record, retained for 15 years under cl 9, holds the owner, serial number, any porous material added, attachment replacements, tare changes, the result with reasons for failure, the retest date, the station and the retester.

A rejected cylinder is rendered unserviceable by crushing or by irregular cutting into three or more pieces including the shoulder (cl 10, per IS 9200). Clause 11 notes that residual acetylene, solvent and a mass that may contain asbestos make the methods used for other cylinders inappropriate. Under Rule 36(1) a cylinder that fails, or that has lost more than 5 % of its tare weight, is not filled and is destroyed.