Standard Guide for Cleanliness Levels and Cleaning Methods for Materials and Equipment Used in Oxygen-Enriched Environments

Importancia y uso:

4.1 The rationale for cleaning materials, components, and systems for oxygen service is predominantly related to the risk of ignition and fire, but other performance aspects also benefit from cleaning. Thorough cleaning is considered a fundamental fire safety measure applied to oxygen systems. Contaminants may not only result in malfunction or process anomalies, but are also potential fuels. Materials become more flammable and more readily ignitable as oxygen concentration, pressure, and temperature increase. Contaminants, particularly in the form of hydrocarbon oil or grease surface films, have been shown to be more readily ignitable than the bulk materials of a component or system by ignition mechanisms such as compression heating (Guide G88). If present in sufficient quantity, ignition and subsequent combustion of contaminants has the potential to ignite other materials, possibly developing into a kindling chain involving the bulk materials of the component or system. Likewise, solid contaminants, particularly metal debris, may be ignitable either directly by ignition mechanisms such as particle impact (Guide G88), or become a secondary element in a kindling chain initiated by ignition of oil or grease contaminants. Therefore, avoiding contaminants is paramount in developing, operating, and maintaining a safe oxygen system.

4.2 Cleaning for oxygen service is recommended for any system or component that is exposed to oxygen-enrichment (oxygen or other oxidizers) or those that interface oxygen systems that could either inadvertently be oxygen-enriched or supply potential contaminants into the oxygen system. The definition of an oxygen-enriched atmosphere (OEA) can vary by industry, but is defined in Terminology G126 to be concentrations above 25 mol percent oxygen. Furthermore, high-pressure or high-temperature air systems, or both, (~21 percent oxygen) may also benefit from cleaning in accordance with the guidance of this document. Historical fires have been observed in high pressure air systems where contaminants were ignited.

4.3 This guide furnishes qualified technical personnel with guidance in the specification of oxygen system cleanliness needs. However, it does not specify cleanliness levels for industries or specific applications. While examples of cleanliness levels used by various industries or applications are provided for reference, specific applications may require more or less stringent cleanliness.

4.4 Another primary purpose of this guide is to furnish qualified technical personnel with information regarding selection of cleaning methods and associated practices for materials and equipment to be used in oxygen-enriched environments.

4.4.1 General methods, apparatus, and reagents for cleaning materials and equipment used in oxygen-enriched environments are described in this guide. Exact procedures are not given because they depend on the contaminant type and material to be cleaned, cleaning agent used, and degree of cleanliness required. Methods may be used individually, or may be combined or repeated to achieve the desired results. Examples of cleaning procedures that have been successfully used for specific materials, components, and equipment in selected applications are described in the appendices. An index of the specific materials, components, equipment, and applications covered in these examples is given in Table X1.1.

4.5 Methods to qualitatively or quantitatively evaluate the cleanliness of materials or components cleaned for oxygen service are provided. These techniques may be used to validate new or revised cleaning processes to demonstrate that target cleanliness levels are being achieved, routinely inspect cleaned parts as part of a quality control sampling, or to evaluate in-service cleanliness of components or systems.

4.6 The cleanliness achieved from the cleaning process should be preserved until the material or component is put into oxygen service. Principles and best practices regarding the cleaning environment, packaging and labeling of cleaned items, and assembly practices to maintain cleanliness are discussed.

Subcomité:

G04.02

Referida por:

G0122-20

Volúmen:

14.04

Número ICS:

71.040.20 (Laboratory ware and related apparatus)

Palabras clave:

cleaning; cleanliness verification; contamination control; NVR; oxygen; oxygen-enriched environments; oxygen service; oxygen systems; particulate; precision clean;