REACH - Applications for authorisation AFA046-01 Chromium trioxide

Closed 22 Sep 2023

Opened 28 Jul 2023


Public consultation on alternatives

Reference: AFA046-01

Applicant: APPH Ltd.

Application type: Initial

Substance name: Chromium Trioxide

EC Number: 215-607-8 

CAS Number: 1333-82-0 

Annex 14 Entry Number: 16 

Proposed use: Use of chromium trioxide for functional chrome plating of aircraft components for civil & military sectors that meet the airworthiness requirements and hydraulic components for military vehicles.

Broad information on use applied for (conditions of use and function): APPH Ltd. (also known as Héroux-Devtek UK) uses chromium trioxide for functional chrome plating in the production and maintenance, repair and overhaul (MRO) of aircraft components for military and civilian sectors at its production site in Runcorn, England. The chrome plated components include structural parts of landing gear systems as well as items such as hydraulic units (e.g. actuators, valves, accumulators) and flight controls. In addition, HD UK chrome plates hydraulic components for military vehicles.

Functional chrome plating is an electrolytic process in which a layer of metallic chrome (Cr0) is deposited on the substrate from a hexavalent chromium (CrVI) plating solution based on chromium trioxide. A sulphuric acid based or chromium trioxide based activation step known as etching is performed (in a separate activation bath or directly in the plating bath) to make the component surface more receptive to chrome plating, improving the adhesion of the coating. The finished chrome plated components are completely free of CrVI.

The function of the chrome plating is to protect the aircraft and vehicle components against wear and corrosion, thus increasing the component durability and service life. The unique properties of the chrome coating include:

  • Wear resistance
  • Hardness
  • Corrosion resistance
  • Low coefficient of friction
  • Surface finish
  • Strong adhesion to base material
  • Layer thickness

These properties are key for ensuring the successful operation of the aircraft and military vehicle components in very harsh, challenging and safety critical environments. Thanks to these properties and the inherent crack pattern which provides lubricant retention, functional chrome plating is particularly suited for coating of gas/oil sealing surfaces. In addition, the key process related functionalities of CrVI based functional chrome plating include low process temperature which does not cause any distortion or dimensional changes to the base material, compatibility with different substrate geometries and the possibility to rebuild/repair worn or damaged components.

List of descriptors:

  • Sector of end Use (SU): 17 (General manufacturing, e.g. machinery, equipment, vehicles, other transport equipment).
  • Product category (PU): 14 (Metal surface treatment products).
  • Process category (PROC): 1, 8b, 13, 28, 0.
  • Environmental release category (ERC): ERC6b.
  • Technical function (TF): Plating agent.

Annual tonnage used: 0.5 – 1.5 tonnes per annum

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).


  • Applications for authorisation


  • Registration, Evaluation, Authorisation & restriction of CHemicals (REACH)