Corrosion at steam lines varies widely; its rate and aggressiveness being dependent upon many factors.  In fact, it is the steam condensate itself which produces most of the damage – leaving the original design of the system and its maintenance as the factors most responsible for long service.  High pressure steam usually suffers less impact due to steam condensate give its higher temperatures less favoring condensate creation.  Critically important steam traps, if not maintained and allowed to fail, will either blow steam and waste money, or more importantly – allow steam condensate to collect and potentially destroy the bottom of the pipe.

Service life is significantly dependent upon the quality and corrosion resistance of the pipe, piping schedule, system design, and steam quality.  At the same time we have documented steam pipe from the late 1800s still at or above its original thickness specification, we have documented new 10 year old steam pipe with only 5 more years of service life left.  Given that corrosion activity is always greater for the steam condensate lines due to the presence of weak carbonic acid in the condensate, corrosion rates are typically 3 times higher – 1.5 MPY for the condensate side as opposed to under 0.5 MPY for the steam supply.

Whereas most steam systems were constructed of extra heavy pipe many decades ago, the use of schedule 40 pipe has now become the standard even for high pressure service.  Most steam condensate systems still remain heavier schedule 80 pipe due to the recognized higher corrosion they endure.  Thinner schedule 40 pipe, however, is occasionally identified.  Given the inherent dangers of high pressure steam service, all threaded pipe should be schedule 80.  Yet the discovery of random examples of thinner schedule 40 pipe during an ultrasonic piping investigation is not unheard of – the result of carelessness or a lack of concern.

The addition of filming amines to any boiler water chemical treatment program is always advised given that it carries over with the steam to provide a protective coating to the steam lines, as well as raise condensate pH, thereby reducing its corrosiveness.

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