Выражение встречается в следующем контексте:
Petrotherm electric HEATER LOGS provide efficient in-line pre-heating of fuel oils in steam generators. They are also used in auxiliary tank heating for smaller tanks or low production rates. The HEATER LOGS use threee to nine heating elements mounted on a flange-header assembly. The elements are individually replaceable in case of heater burn-out, cutting replacement costs by a factor of four.
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