EN 1797-2001 pdf download.Cryogenic vessels – Gas / material compatibility.
The selection of a material for use with oxygen and/or in an oxygen enriched atmosphere is pnmanly a matter of understanding the circumstances that cause oxygen to react with the material. Most materials in contact witti oxygen will not ignite without a source of ignition energy. When an energy input rate, as converted to heat, is greater than the rate of heat dissipation, and the resulting heat increase is continued for sufficient time, ignition and combustion will occur. Thus, two things shall be considered
the materials minimum ignition temperature;
— the energy sources that will produce a sufficient increase in the temperature of the material.
These should be viewed in the context of the entire system design so that the specific factors listed below will assume the proper relative significance.
The specific factors are:
the properties of the materials, including the factors affecting ease of ignition and the conditions affecting potential resulting damage (heat of reactIon):
the operating conditions : pressure, temperature, gas velocity, oxygen concentrations and oxygen state (gaseous or liquid), surface contamination in accordance with EN 12300;
the potential sources of ignition (friction, heat of compression, heat from mass impact, heat from particle impact, static electricity, electrical arc, resonance, Internal flexing etc.);
the reaction effect (consequence on the surroundings etc.);
additional factors (performance requirements, prior experience, availability and cost).
CAUTION This European Standard specifies the minimum acceptance requirements for materials in oxygen and enriched air service. In the cases of severe conditions and when the operating pressure ls above 40 bar, additional tests to those specified should be considered.
The use of materials in cryogenic vessels which do not pass the tests outlined in 4.4.1 and/or 4.4.2 shall be supported by a favourable risk assessment andior documented evidence of previous long term satIsfactory service in use.
4.2 Evaluation of metallic materials
Metallic materials normally used for the construction of cryogenic vessels i.e. low alloy steels, nickel steels. stainless steels, copper and copper alloys, aluminium and aluminium alloys do not normally present any incompatibility when in contact with oxygen.
The cases in which some ignitions or violent reactions may occur are when very thin materials are used with high surface/volume ratio, and when high ignition energy is available e.g. pump failure. Thin materials e.g. thinner than 0,1 mm shall be tested In accordance with 4.4.2 in conditions as close as possible to the real operational conditions (e.g. for muIti layer insulations use similar number of layers and configuration). Materials to be used In applications where the ignition energy is potentially high should be subjected to special consideration.
For cryogenic vessels intended for oxygen service the test shall be performed with oxygen. For cryogenic vessels intended for nitrogen, hydrogen or helium service, when materials are located in an area where contact with condensed enriched air is a risk, the test described in 4.4.2 shall be performed with cryogenic 0JN2 mixtures
containing at least 50 % oxygen.
4.3 Evaluation of non metallic materials
Non metallic materials include, for example, plastics, elastomers, lubncants. ceramics, glasses and glues. Some of these materials present a high risk of ignition when in contact with oxygen and should be avoided or carefully selected and used in limited quantity.
Some fully oxidised materials such as ceramics and glass present no risk of ignition provided they are not contaminated.
Any non metallic materials, other than fully oxidised materials, in contact with liquid oxygen shall be tested in accordance with 4.4.1 and 4.4.2. Consideration shall be given to testing materials used in those parts of the system where liquid oxygen accumulation may incidentally occur (e.g. in the insulation).
For cryogenic vessels intended for oxygen service the test shall be performed with oxygen. For cryogenic vessels intended for nitrogen, hydrogen or helium service, when materials are located in an area where contact with condensed enriched air is a risk, the test described in 4.4.2 shall be performed wfth cryogenic OJN, mixtures
containing at least 50 % oxygen.
Any non metallic materials, other than fully oxidised materials, in contact with gaseous oxygen shall be tested in accordance with 4.4.1. Consideration shall be given to testing materials used in those parts of the system where gaseous oxygen accumulation may incidentally occur (e.g. in the insulation).EN 1797-2001 pdf download.