Effluent treatment in MT

July/August 2011

1- Introduction

MT effluents are less problem-prone than effluents from PT lines.

Chemical formula and how MT products are used are the main points.

This topic was dealt with in a conference(*) given by one of us, and this paper is an update.

2- Materials used in MT

Materials used in MT are:
• Magnetic powders to be put in suspension in water.
• White contrast aid paints.
• White contrast aid paints solvent removers
• Oil-based magnetic inks supplied as concentrates or ready-to-use.
• Water-based magnetic inks.
• Magnetic particles to be put in suspension in either water or oil.
• Dry magnetic powders.
• Oil-based carrier liquids used to dilute concentrates or to be mixed with powders.
• Conditioning agents to prepare water-based magnetic inks.

2.1 White contrast aid paints

Some white contrast aid paints are peelable (also called ‘‘strippable’’) and therefore easier to remove than non-peelable ones.

They are all made of a suspension of inert white pigments in organic solvents (such as: acetone, ethyl acetate and isopropanol) containing resins and plasticizers in solution. They are generally supplied in spray cans and less often in 5 or 10 L containers.

After the solvent has evaporated, a non-hazardous white residue is left on the surface.
Unused or expired materials may be settled, to extract solids from liquids.

Liquids may be disposed of in suitable licensed facilities.
White solid residues are inert and suitable for disposal in approved landfill sites.

Containers and spray cans boxes are disposed of in suitable licensed facilities.

Volatile organic compounds (VOC) percentage of these paints is about 80% Weight/Weight of the spray can content.

There are organic solvent-free white contrast aid paints. Some are made of inert pigments in suspension in an aqueous vinyl polymers emulsion.
They are generally supplied in 5 or 10 L containers but not in spray cans.
Since they do not contain any volatile organic compound (VOC), their drying time is far too long and they are used mainly in hot areas.

2.2- White contrast aid paints solvent removers

Acetone may remove white contrast aid paints but specifically designed solvent removers in spray cans are much better.
Quite a long time ago, and before the Montreal Protocol was enforced, they were 1,1,1, trichloroethane-based; later trichloroethylene has been used.

Meanwhile trichloroethylene has been classified as harmful, in the Council Directive 67/548/ECC dated June 27, 1967; but the 28th adaptation to technical progress, through the Commission Directive 2001/59/EC of August 6, 2001 modified its labelling, which is now:

• Toxic with the skull-and-crossbones symbol displayed.

Plus the following risk sentences:
• R 45 May cause cancer.
• R36/38 Irritating to eyes and skin.
• R52/53 Harmful to aquatic organisms, may cause long-term adverse effects in the aquatic environment.
• R67 Vapours may cause drowsiness and dizziness.
• R68 Possible risk of irreversible effects.

This is why trichloroethylene can be used ONLY as a vapour degreaser in suitable installations complying with current regulations.

As a matter of fact, nowadays, white contrast aid paints solvent removers are ethyl acetate-based.

Spray cans boxes are disposed of in suitable licensed facilities.

The volatile organic compounds (VOC) percentage is about 98% Weight/Weight of the spray can content.

2.3- Oil-based magnetic inks supplied as concentrates or ready-to-use

Oil-based magnetic inks may be supplied either as concentrates or ready-to-use. They are made of a suspension of very fine magnetic particles in a hydrocarbon blend dearomatized by catalytic hydrogenation. Ready-to-use magnetic inks are supplied in 5 L, 10 L or 25 L containers. Concentrates are supplied in 200 mL or ½ L bottles.

Unused or expired materials and their containers are disposed of in suitable licensed facilities.
Used materials may be decanted.
Hydrocarbon blends are no longer burned as in the past but now they are recovered to be reclaimed.
Solid residues made of magnetic particles are inert and suitable for disposal in approved landfill sites.

Containers and spray cans boxes are disposed of in suitable licensed facilities.

One of our papers (**) already published on our Website deals with their VOC content.

2.4- Water-based magnetic inks

- 2.4.1- Supplied as concentrates

The magnetic inks may be prepared from:
• Liquid concentrates.
• Magnetic particles and conditioning agents supplied as separate chemicals.
• Powders made of a blend of magnetic particles and conditioning agents.

Automotive industry and railways industries are by far the largest users of water-based products, when aerospace industry is imperviously against.

Water-based magnetic inks are made of a suspension of very fine magnetic particles in an aqueous solution of surface-active agents (surfactants), nitrite-free corrosion inhibitors, rheologic agents and (generally silicon-free) antifoam agents. Liquid concentrates are supplied in 200 mL or ½ L, 5 L or 10 L containers. Magnetic powders are supplied in 1 or 5 kg cans.

Unused or expired materials and their containers are disposed of in suitable licensed facilities.
Solid residues mainly made of magnetic particles are inert and suitable for disposal in approved landfill sites.

Containers are disposed of in suitable licensed facilities.

As a general rule in automotive industry, a brand-new water-based magnetic ink is used at the beginning of every shift.

French regulation, and probably regulation in other countries, state, among different requirements, that the effluents disposed of into sewers or rivers shall be clear and without any colour.

Other requirements come atop these basic ones:
• Maximum acceptable content of metals (chromium, iron, nickel, aluminium, etc.)
• Content of total suspended solids (TSS).
• pH which should be between 5.5 and 8.5.
• Temperature equal to or less than 30°C (86°F).
• Maximum allowable content of hydrocarbons.
• BOD5 (Five-day biochemical oxygen demand) and COD (chemical oxygen demand) according to the daily flow: bacteria which degrade surface active agents, for instance, need a lot of oxygen.
• Etc.

Therefore, water-based magnetic inks must be treated before discharge; this is not a difficult task as the product, when used, is diluted in water at about 1 to 5% maximum.

Their volatile organic compounds (VOC) percentage is equal to 0% Weight/Weight.

- 2.4.2- Supplied in spray cans

A manufacturer markets new non-flammable spray cans of water-based magnetic inks with carbon dioxide propellent.

Three colours are available: black, fluorescent yellow-green under (UV-A) ultraviolet radiation and a product red under white light and orange-red fluorescent under (UV-A) ultraviolet radiation.

Their volatile organic compounds (VOC) percentage is equal to 0% Weight/Weight of the spray can content.

Spray can boxes are disposed of in suitable licensed facilities.

2.5- Magnetic particle for suspension in either water or oil. dry magnetic powders

Solid residues made of magnetic particles are inert and suitable for disposal in approved landfill sites.

Unused or expired materials and their containers are disposed of in suitable licensed facilities.

Containers are disposed of in suitable licensed facilities.

Their volatile organic compounds (VOC) percentage is equal to 0% Weight/Weight.

2.6- Oil-based carrier liquids

They are used to prepare magnetic inks either from magnetic particles or from oil-based magnetic ink concentrates.

Unused or expired materials and their containers are disposed of in suitable licensed facilities.

These hydrocarbon blends are no longer burned as in the past but now they are recovered to be reclaimed.

Their volatile organic compounds (VOC) percentage is equal to 100% Weight/Weight.

2.7- Conditioning agents

Conditioning agents are used together with magnetic particles to prepare water-based magnetic inks.

They are blends of surface active agents (surfactants) and corrosion inhibitors. They are supplied either in the liquid form (generally in tins of 5 L or 25 L containers) or as powders (generally in 1 or 5 kg jars).

Unused or expired materials and their containers are disposed of in suitable licensed facilities.

Their volatile organic compounds (VOC) percentage is equal to 0% Weight/Weight.

3- Trends for the future

Many companies in Europe want to be ISO 14001:2004 certified. ISO 14001/2004 standard is THE standard dealing with environment. Among many items, it requires that companies reduce their VOC emissions. Therefore the first step is to know which products contain VOC.

Water-based magnetic inks supplied as concentrates and spray cans are likely to be THE answer for the future.

This solution has already been in use in the automotive and railroad industries for many years.

Solvent-free white contrast aid paints available on the market, as seen above, have a too long drying time.
There is therefore a need to design such a material, easy to apply and quick to dry: on site, it is not that easy to carry out MT under ultraviolet radiation (UV-A). Unfortunately, the volatile, odourless, non-VOC ... just does not exist ... High flammability of such a solvent is the price to pay for a quick drying.

On critical parts with a machined surface, due to wettability and corrosion reasons, oil-based magnetic inks are preferred: aerospace industries use only these MT materials, and we do not see any change in the foreseeable future.

Reference

(*) Pierre CHEMIN : Traitement des effluents en ressuage et en magnétoscopie, produits à base pétrolière ou à base aqueuse (Editor’note : Effluent treatments in PT and MT, oil-based or water-based materials). ‘‘NDT and environment Conference’’ October 1998 - Metz (France) organized by the Eastern Regional Group of COFREND (French Confederation for Non-Destructive Testing).

(**) Pierre CHEMIN and Patrick DUBOSC, Oil-based and water-based magnetic inks, October 2010, on our Website:
http://www.ressuage-magnetoscopie-penetranttesting-magnetictesting-dpc.info/site/en/news/mt-texts/177-liqueurs-magnetiques-a-support-petrolier-et-a-support-aqueux

• ISO 14001:2004 Environmental management systems -- Requirements with guidance for use, International Organization for Standardization, Geneva, Switzerland, 2004.