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Cleaning Equipment for Oxygen Service

Keywords: Cleaning, Medical, Oxygen, Piping, System, and Prevention.

1. Introduction:

Oxygen is not flammable in itself but supports combustion Oxygen can react with most materials. The higher the oxygen content and/or pressure in a system:

  • The more vigorous the combustion up to explosive levels.
  • The lower the ignition temperature, up to ignition of materials that normally do not burn in atmospheric air.
  • The higher the flame temperature and combustion velocity.

Care must be taken in the selection of equipment and materials, which need to be oxygen compatible and free from contaminants. The main contaminants to be avoided and/or eliminated are hydrocarbon oils and greases, which are easily combustible and particulate matter, which can easy ignite or cause ignition.

Recognition of oxygen's reactivity led to stringent requirements regarding cleanliness of equipment in oxygen service.

The first edition of this document issued 1986 recommended procedures and agents to clean and maintain the cleanliness of surfaces in contact with oxygen, inspection methods and acceptance criteria as well as practical examples.

Cleaning with solvents (as a main procedure at that time in the oxygen industry) was recommended in most examples.

The increasingly stringent environment regulations of the last years, regulations including the phasing out of most chlorofluorocarbons (CFC), restrictions in the use and the banning of some volatile organic compounds (VOC) led to the necessity to develop alternatives.

2. Scope and Purpose:

This document deals with the cleaning of equipment or parts to be used in contact with gaseous or liquid oxygen and nitrous oxide or oxidizing gases/mixtures with and oxygen index > 25%.

Particularly, this document describes cleaning methods, lists cleaning agents, presents inspection methods and ways for conservation of cleanliness.

3. Cleaning Methods

3.1 Procedure and Agent Qualification
3.1.1 General

This provides information to be considered when selecting a cleaning procedure/agent for an oxygen system.

Before a decision is made about which cleaning method has to be used, the need for cleaning must be considered and established.

3.1.2 Selection Criteria

The procedure/cleaning agent should ideally meet the following criteria:

  • Technical:
  • Good degreasing properties
  • Easily removable
  • Non-Corrosive
  • Compatible with commonly used metallic and non-metallic materials
  • Cleaning agent and its residue to be compatible with oxygen
  • Non-Flammable or low flammability
  • Environmental / Safety:
  • Non-Toxic
  • Non-Ozone depleting
  • Environmentally safe
  • Disposable
3.1.3 Additional Technical Criteria

Other technical aspects to be considered are:

  • Size of Parts:
  • Small parts (e.g. up to 500mm).
  • Big parts as compressor casings, heat exchangers, vaporizers.
  • Form of Parts:
  • Simple.
  • Complicated/dead ends, crevices.
  • Elongated (pipes).
  • Surface to be cleaned:
  • Inner.
  • Outer.
  • Roughness.
  • State of the equipment to be cleaned:
  • Assembled.
  • Disassembled.
3.1.4 Health, Safety and Environmental Aspects

The ideal agent is non-toxic or at least has a low toxicity. The main factors to take into consideration are: Inhalation effects, Skin effects, Eye effects.

3.1.5 Typical Methods

Typical methods for cleaning of components, vessels and pipe work systems used in oxygen service, Chemical cleaning, or Detergent cleaning.

3.1.6 Chemical Cleaning

Chemical cleaning is a process involving acid or solutions and is used to remove the following alkaline type of contaminants: Heavy or tenacious surface adherents, Rust, scale and oxide films, Brazing fluxes, small amounts of paint, grease, oil film and drawing compounds.

Acid cleaning is not generally used for the removal of oils and grease; these contaminants, if present, should be removed by a solvent or by an alkaline solution prior to acid pickling.

Chemical cleaning relates to the cleaning of components by the following alternatives: Immersion in a tank containing the cleaning material. Addition of some kind of mechanical energy is normally required. Spraying the equipment with the cleaning liquid. Complete filling of the components with the cleaning material. This may be applied to large pieces of equipment.

The cleaning materials are used as aqueous solutions of either acids or alkaline products. The solutions prepared will be in concentrations appropriate to the materials used in the construction of components and the surface condition required. Multiple cleaning operations are sometimes necessary to treat some metal surfaces, e.g. passivation to retard corrosion.

After the completion of the chemical cleaning operation, by either acid or alkaline solution, all residual cleaning fluid must be completely drained from the component by flushing with clean oil-free water and purged.

3.1.7 Acid Cleaning

This is normally carried out with an aqueous solution of acids at ambient temperature. Phosphoric acid cleaning solution can be used for metals, for the removal of oxides, light rust, light soils, fluxes and certain protective coatings.

Hydrochloric acid solutions can be used for carbon and low alloy steels only. This solution will remove rust, scale, oxide coatings and will strip chromium, zinc and cadmium plating.

Chromic and nitric acid solutions can be used for cleaning aluminum, copper and their respective alloys. These solutions in themselves are not adequate cleaning agents, but are regarded as de-oxidizers for brightening metals dulled by alkaline solution cleaning. Nitric acid solution in combination with copper and copper alloys produces toxic fumes, and therefore good ventilation is essential.

After cleaning, all components shall be thoroughly rinsed, using flowing oil-free water, preferably hot to acid drying, unless otherwise specified by the supplier of the chemical materials. Special care should be given to carbon and low alloy steel components.

3.1.8 Solvent Cleaning

This cleaning or degreasing method has to a great extent been replaced by other methods because of safety and environmental reasons. In certain situations where other cleaning methods cannot be applied, solvent cleaning may be considered.

Before starting a cleaning operation a reference sample of fresh clean solvent shall be retained. This sample will be used as a base reference. At intervals throughout the procedure, samples of used solvent shall be taken. These can be compared with the reference sample to determine the level of contamination and the cleaning procedure continued until the acceptance standard of cleanliness is reached.

4. Inspection Records:

Records are made of inspections and acceptances for the cleaned equipment or assembly. The record will include: Identification of the item covered, Cleaning method employed, Method of inspection, Results of inspection, Inspector's signature and date.

5. Labeling for Oxygen Service:

All equipment components and spare parts delivered single or bulk packed in accordance with this specification shall bear a label stating that the items have been "CLEANED FOR OXYGEN SERVICE".

Additional information may be included as follows: Showing date of operator number and run letter.

6. Conservation of Cleanliness:

Once a piece of equipment has been cleaned for oxygen service and certified as conforming to the cleanliness specifications shall be protected to prevent contamination.

The protection provided will depend on a number of items such as the size and type of equipment, method of shipping, duration, and conditions of storage. The packaging material used shall be clean, strong, to be sealed, waterproofed and suitable for the purpose.

7. Protection Methods:

7.1.1 Small Equipment

Accessories or parts such as valves, gaskets, etc. shall be packaged individually, after cleaning in a clean polyethylene tube or bag and sealed.

7.1.2 Large Equipment

Openings on equipment shall preferably be sealed with degreased caps, plugs, or suitable blind flanges.

7.2 Notes

The packing must be carried out in the area(s) temporarily or permanently allocated to equipment for oxygen service. All equipment shall be labeled.

8. Design and Manufacturing Considerations for Cleanliness:

The ability to clean, and the methods(s) used in the design of equipment, room and components for oxygen service.