System – Steam

• Overview

Steam systems have been in existence the 1800’s and are still used in building properties to this day – especially at older buildings.  Central powerplants producing steam are the backbone of most larger college campuses where they provide power to both heat and cool.  Cities like New York City maintain an extensive network of high pressure steam lines under the street serving most larger high rise office buildings.  For smaller properties like schools, a smaller on-site steam boiler likely exists.

For one investigation, we identified a one pipe steam system from the late 1890s still approaching schedule 80 specifications and capable of providing another 100 plus years of reliable service.  This amazing result from before the time a 2nd pipe was used to carry condensate, and that single line supplied steam and returned condensate.  Of course, pipe quality was far superior at that time.

Our ultrasonic investigations typically identify very favorable results when testing steam pipe, and especially older and heavier steam pipe.  When properly maintained, steam systems have the ability to provide virtually unlimited reliable service.

• Common Problems

In general, steam itself has a low corrosive impact to carbon steel, and will produce low and extremely uniform corrosion rates typically below 0.3 MPY.  A visual inspection of 100 year old steam pipe can show just light surface rust uniformly around the inside wall.  External corrosion is typically not a problem unless the pipe runs underground.  The main problem to all steam piping systems is created by the condensate that can form.  Due to the weak carbonic acid it contains at lower pH, steam condensate can severely etch and selectively corrode or pit areas of the steam pipe causing failure.  Low pressure steam systems operating under 10 psi are most vulnerable to corrosion attack caused by the greater potential for condensate production; a problem always possible but less frequently found at high pressure systems.

• Major Threats

Unlike a leak which may occur to other piping systems such as domestic water or chill water, a leak at a steam system has the potential to cause a massive explosion and critical injury should anyone be near the point of failure, with that threat raised at larger diameter and higher pressure lines.  Common threats to all steam systems are:

• • • Inadequate incline or grade
    • A reverse grade collecting condensate
    • Installed location below chilled water or cold water pipe
    • Highly corrosive condensate
    • Inadequate insulation
    • Rust blocked or malfunctioning steam traps
    • Inadequate steam trap use
    • Improper fitting-up of welded pipe allowing an internal ridge
    • Pipe of different schedules or age fitted together
    • Improper on-site boiler water chemical treatment
    • Improper welding
    • Failed underground Rickwell or other external protection
    • The use of schedule 40 threaded pipe
    • The installation of standard cast fittings rather than forged
    • The use of brass valves

Aside from the failure of the pipe itself, multiple components to a steam supply system are also subject to the same forces.  Strainers and valves have been known to explode with a result destroying the entire surroundings.  Steam expansion bellows, although extremely reliable, can also fail explosively under certain conditions.  In short, every single component of a steam piping system has certain vulnerabilities which increase with age and pressure.  Unlike the pipe itself, most such components cannot be tested, and instead must be judged by the expected service interval and replaced when due.

• Testing Focus
  

Any UT investigation of a steam supply system should include:

• • • Largest mains
    • Areas of negative incline
    • Bottom areas near steam traps
    • Steam trap piping
    • Threaded pipe
    • Smallest diameter pipe
    • Pressure reducing stations
    • By-pass lines

Performing routine maintenance of the condensate traps or acoustical stream trap testing in order to ensure that all are properly functioning is critically important for all steam systems.  Reasonably assume that any higher corrosion activity acting against the steam pipe is also acting against all related steam components.  Verify that all smaller threaded steam pipe is installed using extra heavy schedule 80 seamless pipe.  Prohibit ERW seamed pipe for any steam pipe service.

Corrview maintains a large photo gallery specifically related to steam and steam condensate piping in addition to other corrosion related issues. To visit our gallery on steam and steam condensate piping, please click here

© Copyright 2023 – William P. Duncan, CorrView International, LLC