REACH - Applications for authorisation AFA031-01 - Multiple Cr(VI)

Overview

Public consultation on alternatives

Reference: AFA031-01

Applicant: 

Brenntag UK Ltd (SD, PD)
Wesco Aircraft EMEA Ltd (CT, DtC)

Application type: Review

Substance name: 

Chromium trioxide (includes “Acids generated from chromium trioxide and their oligomers", when used in aqueous solutions) (CT)
EC 215-607-8    CAS 1333-82-0

Sodium dichromate (SD)
EC 234-190-3     CAS 10588-01-9

Potassium dichromate (PD)
EC 231-906-6     CAS 7778-50-9

Dichromium(tris) chromate (DtC)
EC 246-356-2     CAS 24613-89-6

Proposed use: Chemical conversion coating using chromium trioxide, sodium dichromate, potassium dichromate, and/or dichromium(tris) chromate in aerospace and defence industry and its supply chains.

Broad information on use applied for (conditions of use and function): 

Chemical conversion coating (CCC) is a chemical process applied to a substrate producing a superficial layer containing a compound of the substrate metal and elements from the processing solution. The term “chemical conversion coating” is used for both the process and the resulting coating layer. Conversion coating removes the native oxide and replaces it with an oxide that has predictable and stable properties, formed from the substrate metal and the processing solution. We define conversion coating as “a chemical process that introduces a chemical coating or changes the surface of the substrate to improve the substrate properties (e.g., corrosion resistance or to promote adhesion of subsequent coatings).”  Note that the conversion coating layer itself is not corrosion resistant, but it provides improved corrosion resistance to the substrate. In general, conversion coating forms an adherent, fixed, insoluble, inorganic crystalline or amorphous surface film of complexes from oxides and hydroxides and chromium trioxide as an integral part of the metal surface by means of a chemical reaction between the metal surface and the immersion solution.  Typical thickness of the coatings is 0.05-2.00 μm. The coatings are typically in the lower thickness range (below 0.5 μm). 

The key functions of the four chromates in CCC include: Corrosion resistance including active corrosion inhibition ("self-healing"), chemical resistance, adhesion promotion, temperature resistance, layer thickness, and electrical resistivity. These functions are relevant to all four chromates, and their use across all application methods, e.g., immersion versus brush/swab and touch-up.  Impact on fatigue life is also considered when assessing test candidates for Cr(VI) for conversion coating, as well as pre-treatment compatibility and the ability to visually determine that the conversion coating has been appropriately and uniformly applied (inspectability).
Brenntag UK Ltd are seeking authorisation for chemical conversion coating using sodium dichromate and potassium dichromate, whilst Wesco Aircraft EMEA Ltd are seeking an authorisation for chemical conversion coating using chromium trioxide and dichromium tris(chromate). 

The applicants have identified a shortlist of potentially suitable alternatives. Due to the complexity of design challenges, performance requirements, safety requirements and regulatory controls that must be tested for each listed alternative, and the need for industrial implementation in the whole supply chain, the applicant is seeking a review period of 12 years.  
This “applied for use” involves the continued use of Chromium trioxide, Sodium dichromate, Potassium dichromate and Dichromium tris(chromate) across approximately 80 sites across Great Britain (GB).

List of descriptors:

• Sector of end use (SU): Other: Aerospace and defence industry and its supply chains
• Environmental release category (ERC): 5
• Process category (PROC):0, 5, 8b, 9, 10, 13, 15, 21, 24, 28 
• Product category (PC): 14- Metal surface treatment products 
• Article Category related to subsequent service life (AC): N/A 
• Technical Function: Corrosion resistance including active corrosion inhibition ("self-healing"); Chemical resistance; Adhesion promotion; Temperature resistance; Layer thickness; Electrical resistivity

Annual tonnage used: 

• Up to 30 tonnes/year (chromium trioxide)
• Up to 7 tonnes/year (sodium dichromate)
• Up to 6 tonnes/year (potassium dichromate)
• Up to 1 tonne/year (Dichromium tris(chromate))

Review period requested: 12 years

How to submit comments

Provide some basic information on possible alternative(s) in the online survey below but more detailed information should be provided in document(s) prepared using the commenting templates in the related section below. A “public version” should always be completed and will be published after the consultation has closed. If you want to include confidential information in your submission, please additionally complete a “confidential version” and submit both versions as attachments.

The consultation lasts for 8 weeks (unless otherwise specified) and closes at 23:59 London time (BST).