Corrosion caused by trapped moisture under insulation in outdoor piping and
vessels may be a problem. Operating temperatures, intermittent service
conditions, system layout, weatherproofing, and system orientation are all factors
to be considered to avoid the problem. External coatings on the piping and
vessels should be considered to reduce the risk.
Aluminum and aluminum alloys to be embedded in concrete should be isolated
from the concrete material to reduce corrosion concerns. The isolation may be
accomplished by coatings or separating materials.
Limiting the use of polymeric and fiberglass materials should be considered if
there is possible exposure to organic compounds, such as solvents and aromatic
hydrocarbons. Polymeric materials and certain resins in fiberglass materials may
be susceptible to degradation by the organic compounds. Organic compounds
in the parts per million range may cause degradation, so careful analysis of the
process conditions should be performed. In addition, polymeric materials may be
susceptible to environmental stress cracking when exposed to organic
compounds and strong bases.
Limitations on the use of polymeric materials exposed to ionizing radiation should
be considered due to possible degradation. Radiation degradation includes
and discoloration. Most polymeric materials are suitable for cumulative radiation
exposures of less than 1 X10 4 rads in air. Most thermoplastics (with the
exception of TeflonTM polytetrafluoroethylene (PTFE) and a few others) are
suitable up to 1 X 10 6 rads and may be usable up to 1X10 7 rads. Thermosetting
polymers, such as epoxies and phenolics, and aromatic thermoplastics, such as
polystyrene, polyketones, and polyimides, exhibit resistance to levels up to
109 rads in air. Numerous reference materials provide data on threshold
radiation damage of polymeric materials.
Figures 3, 4, 5, and 6 in Section 2.10.6 of Part I provide information regarding
the effects of gamma radiation on polymeric materials.