United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-34: Heat Tracing Contributes to Corrosion Failure of Stainless Steel Piping

                                                          SSINS No.:  6835
                                                            IN 85-34 

                               UNITED STATES 
                       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 
Addressees: 

All nuclear power reactor facilities,holding an operating license (OL) or a 
construction permit (CP). 

Purpose: 

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 
service. 

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. 



8504250452 
.

                                                            IN 85-34 
                                                            April 30, 1985 
                                                            Page 2 of 2 

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 
office. 



                                   Edward L. Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:   P. Cortland, IE 
                     (301) 492-4175 

Attachment:  List of Recently Issued IE Information Notices 
Page Last Reviewed/Updated Tuesday, November 12, 2013