Information Notice No. 85-34: Heat Tracing Contributes to Corrosion Failure of Stainless Steel Piping
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
April 30, 1985
Information Notice No. 85-34: HEAT TRACING CONTRIBUTES TO CORROSION
FAILURE OF STAINLESS STEEL PIPING
All nuclear power reactor facilities,holding an operating license (OL) or a
construction permit (CP).
This information notice is provided to alert recipients of a potentially
significant problem pertaining to the use of heat tracing, especially with
tubes containing traces of chemical contamination. It is expected that
recipients will review the information in this notice,for applicability to
their facilities and consider actions, if appropriate, to preclude a similar
problem occurring at their facilities. However, suggestions contained ill
this information notice do not constitute NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances:
On December 7, 1984, Pilgrim Nuclear Power Station reported seven through-
wall cracks in 50 feet of type 304 stainless steel piping that was installed
in a horizontal position. The 1 inch piping is part of the postaccident
sampling system (PASS) and the containment atmospheric continuous monitoring
system. The cracks were discovered during final testing, before initial
The piping was installed in August 1984 with heat tracing set for approxi-
mately 270F. During the installation and calibration of the heat
tracing equipment, temperatures were periodically higher in various portions
of the piping. Although the lines were intended to have a slope for draining
purposes, interface requirements led to a horizontal line.
The piping carries gas samples and heat tracing is used to keep it dry.
During installation it was filled with clean water several times for
hydrostatic testing and flushing of the system. The water was removed by
blowing air through the pipe and using the heat tracing for final drying.
During evaporation, the chlorides present in the water concentrated where
the pipe sagged. The combination of concentrating the chlorides, having
regions where the pipes sagged, and applying heat to these areas resulted in
chloride-induced stress corrosion cracking in those regions.
April 30, 1985
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The noteworthy aspect of this event is that the trace chemicals in the water
will concentrate as the water is being evaporated by the use of heat
tracing, The water may be introduced during hydrostatic testing or as
moisture in the gas samples. Repeated evaporation will lead to a buildup of
chemicals and may eventually cause corrosion of the piping that is kept hot
by the heat tracing.
No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this
Edward L. Jordan, Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: P. Cortland, IE
Attachment: List of Recently Issued IE Information Notices
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