Exposure to chemical risks in non-destructive testing and corrosion assessment activities in welding: issues and prevention strategies

Non-destructive testing (NDT) and corrosion assessment processes play a key role in maintaining the integrity of welded metal structures, particularly in demanding sectors such as aeronautics, nuclear power, and marine engineering. These techniques, while essential for ensuring the reliability of structures, expose professionals to a variety of chemical risks whose impact on health should not be underestimated.

The recurring use of organic solvents, developer agents, developing products, and corrosive substances results in potentially harmful exposures for operators. In response to these challenges, the European regulatory framework, particularly the REACH Regulation (EC No. 1907/2006) and Directive 2004/37/EC on carcinogens and mutagens, imposes strict obligations regarding chemical risk management. At the national level, the French Labor Code (Articles R. 4412-1 et seq.) complements this system by specifically regulating the assessment and prevention of these occupational risks.

1. Non-destructive testing techniques and corrosion assessment methods: principles and industrial applications

Non-destructive testing methodologies

NDT techniques are a set of sophisticated approaches for detecting material discontinuities without altering the part being tested. Their classification is based on distinct physical principles:

• Industrial radiography (IR) : This method relies on the use of ionizing radiation, whether X-rays generated by electrical devices or gamma rays emitted by radioactive sources (iridium-192, cobalt-60). Directive 2013/59/Euratom sets a strict framework for protection against the dangers of ionizing radiation, requiring in particular the delimitation of controlled areas and the implementation of individual dosimetry for exposed personnel.

• Ultrasonic testing (UT) : Based on the propagation and reflection of high-frequency acoustic waves, this technique requires the use of couplants, generally glycerin-based gels or special oils, which may contain additives that are potentially irritating to the skin.

• Magnetic particle testing (MT) : This method uses a magnetic field coupled with ferromagnetic particles, often suspended in petroleum solvents. The risks of inhalation of fine dust are governed by the EN ISO 10882 standard on exposure to particles in the workplace.

  
  

• Penetrant testing (PT) : A three-phase process involving successively cleaning the surface, applying a penetrating liquid (colored or fluorescent), and revealing it. The solvents used, frequently based on toluene or xylene (CMR substances), as well as formulations based on trichloroethylene, raise significant health issues.

Corrosion assessment methods and destructive testing

Corrosion tests aim to reproduce and quantify the phenomena of material degradation under controlled conditions:

• Salt spray testing (ISO 9227) : This standard-based approach simulates the extreme conditions of marine environments using sprayed saline solutions. Although primarily using 5% sodium chloride, these tests present risks of equipment corrosion and skin irritation for operators.

• Electrochemical techniques : Polarization methods and corrosion resistance measurements involve the use of electrolytes that are frequently acidic (H₂SO₄, HCl) or basic (NaOH), requiring special handling precautions.

  
  

• Metallographic examinations : The preparation of samples for microstructural analysis involves polishing procedures using abrasive pastes (alumina, diamond) and particularly corrosive microstructural revealing reagents (nital, picral).

  
  

2. Hazardous chemical substances: identification and risk assessment

Non-destructive testing (NDT) techniques involve the use of various chemicals that present specific hazards depending on the methods used. This analysis proposes a classification of the main health risks based on the processes and exposure routes.

1. Industrial radiography: This method uses radioactive sources (iridium 192, cobalt 60) generating a risk of external exposure to ionizing radiation, requiring strict radiation protection measures in accordance with Directive 2013/59/Euratom.

   
   

2. Penetrant testing: This three-functional technique uses:

   - Penetrants based on aromatic solvents (toluene, xylene) classified as toxic for reproduction (category 1B)

   - Cleaners containing chlorinated compounds (trichloroethylene, a proven carcinogen)

   - Powder developers containing amorphous silicas

Occupational exposures can lead to:

• By inhalation: neurological disorders and irritation of the respiratory tract

• By skin contact: allergic dermatitis and defatting of the epidermis

• By ocular projection: severe corneal lesions

  
  

  3. Magnetic particle inspection: This method involves:

• Ferromagnetic particles (iron oxide Fe3O4)

• Hydrocarbon (kerosene) or aqueous vectors

The main dangers lie in:

• Chronic inhalation of fine dust (risk of pneumoconiosis)

• Skin irritations due to polymer additives

  
  

  4. Ultrasound examination: Although less dangerous, this process uses:

• Glycerin-based coupling agents sometimes with added preservatives (formaldehyde)

• Alkaline or solvent pre-cleaning solutions

  
  

Inventory of the main chemical agents in NDT

The following table presents a summary of the most commonly encountered substances:

Substance	Nature of the risk	Classification (CLP)	VLEP (France)
Toluene	Neurotoxicity, reproductive toxicity	H361d, H372	50 ppm (8h)
Xylene	Irritation, narcotic effects	H226, H312, H332	50 ppm (8h)
Trichloroethylene	Carcinogenicity (cat. 1B)	H350	10 ppm (8h)
Perchloroethylene	Hepatotoxicity	H351	20 ppm (8h)

Analysis of exposure pathways

Route of contamination	Products concerned	Immediate effects	Long-term consequences
Inhalation	Organic solvents, dust	Irritations of the mucous membranes	Neurological damage, pulmonary fibrosis
Skin contact	Acids, solvents	Chemical burns, dermatitis	Chronic eczema, sensitization
Accidental ingestion	All products	Gastrointestinal disorders	Liver and kidney damage
Eye projection	Corrosive liquids	Acute conjunctivitis	Vision problems

Corrosive products in welding tests

Corrosion inhibitors containing chromates, while effective, pose major health concerns. Their use is strictly regulated by the REACH Regulation (Annex XVII) and the RoHS Directive (2011/65/EU), with increasingly stringent restrictions on their use.

Mineral acids (HCl, HNO₃, H₂SO₄), essential for certain tests, require special storage conditions in accordance with the decree of March 1, 2024 relating to the storage of hazardous chemical products.

3. Prevention strategies: integrated approach

Engineering measures

Ventilation is the first line of defense against chemical pollutants. Source capture systems, compliant with standard NF EN 1093, should be preferred. For dust, filtration systems complying with standard EN 149 are required.

Substituting the most hazardous substances represents a sustainable solution. This is demonstrated by the replacement of trichloroethylene with less toxic alternatives (d-limonene) or the adoption of less volatile aqueous penetrants.

Personal protective equipment

The selection of PPE must be based on a rigorous risk analysis:

• Respiratory protection : FFP3 masks (EN 149) for dust and cartridge devices (EN 140) for organic vapors are suitable solutions.

• Skin protection : Nitrile gloves (EN 374-3) and type 4 coveralls (EN 14605) provide an effective barrier against chemicals.

  
  

4. Medical monitoring and exposure management

Medical monitoring program

Biological monitoring should include the measurement of heavy metals in urine and hematological parameters for benzene exposure. Respiratory function tests are required for personnel exposed to dust.

Emergency management

Facilities must have eyewash stations and safety showers that comply with ANSI/ISEA Z358.1. Accidental exposure response procedures must be regularly tested.

Conclusion

Managing chemical risks in NDT and corrosion assessment activities requires a systemic approach that integrates technical, organizational, and medical dimensions. Regulatory developments, particularly under the REACH regulation, require constant vigilance regarding the use of chemical substances.

Research prospects should focus on developing less dangerous alternative methods and improving collective protection systems. Continuous training of operators remains a key element for effective prevention of occupational risks in this sector.