A developer that changed habits

Many years ago, solvent-based developers (NAWD) may be 111-trichloroethane-based (T111-based).
At the same time chlorofluorocarbons (CFCs) were the aerosols propellents, mainly a mix of CFC 11 (trichlorofluoromethane) and CFC 12 (dichlorodifluoromethane).

- A fast drying was among the main characteristics of this developer.
- Indications were very clear and the developer may also be useful at quite low temperatures.
- Furthermore, just after application the thin layer of developer appeared as matt white.
- The operator could then check that its application led to a thin, even, homogeneous layer.

But two requirements moved the goalposts:

• In France in the '70s, nuclear industry as well as the aerospace industry asked for chlorine - and sulphur-free spray cans.

• On Jan 1, 1989, the Montreal Protocol forbade manufacturing and use of several chemicals, including CFCs and T-111.

This was kind of a puzzle for penetrant (PT) materials manufacturers as:

• No other propellent could match all the characteristics of CFCs.

• No volatile enough non halogenated solvent is non-flammable.

This way of things can be settled only by some compromise!

Accordingly several PT materials manufacturers chose:

• To use LPG (liquefied petroleum gas), a mix of propane, butane and sometimes isobutane, as propellent.

• To use 2-propanol (also referred to as: isopropanol or isopropylic alcohol) as the non-aqueous volatile liquid.

Operators were startled.

Indeed when applying this new developer they did not have the fast drying product which let them see the matt white layer almost immediately.

The spray cans were lighter than the well-known ones due to the lower specific gravity of LPG and 2-propanol as compared to respectively CFCs and T111. Inspectors inferred that there was not enough powder in the spray can.

As a countermeasure, they sprayed and sprayed the developer...just to see at the end that the developer layer was far too thick for a good job.

The PT materials suppliers got numerous complaints/questions and they had to train the inspectors on how to spray this new kind of product.

Far better to apply one thin layer while firmly pushing down the actuator, then wait for drying, then apply a second thin layer if needed. By experience, the inspectors know the most efficient distance between the nozzle and the part's surface, the most efficient speed they use to spray the surface, and how the developer layer shall come out to get the highest sensitivity.

Nowadays any operator/inspector is accustomed to this developer. Some suppliers add a small amount of 2-propanone (also referred to as: acetone or dimethylketone) to help for a quicker evaporation.

In the '60s a UK Company had a motto: "For every surface treatment problem, there is a product xxxxxx" (trademark we do not display).

Engineers and Commercial people in this Company had made a "translation": "With every surface treatment product xxxxxx (trademark we do not display), there is a problem".

This anecdote is there only to remind everyone that problems met in workshops may be due to the suppliers/manufacturers as well as to the users.

Our idea in these documents is NOT to target anyone, but on the contrary to bring to your knowledge some interesting cases which may prevent you to duplicate the same mistakes while performing Penetrant Testing (PT) or Magnetic Testing (MT).

All the ministories you will read are TRUE. We think they will be helpful:
• First as examples of specific technical --or non-technical-- requirements or peculiar problems.
• Second to let you see that the problems do not always come where you think they should come from.
• Third so that users feel free to ask for help from people (the experts) who may know more than they do.