Information Notice No. 81-07: Potential Problem with Water-Soluble Purge Dam Materials Used During Inert Gas Welding

                                                            SSINS No.: 6835 
                                                            Accession No.: 
                                                            IN 81-07       

                                UNITED STATES
                           WASHINGTON, D.C. 20555
                               March 16, 1981

                                   PURGE DAM MATERIALS USED DURING INERT GAS 

Description of Circumstances: 

Recent experiences with water-soluble purge dam materials at several nuclear
construction sites have shown the need to develop welding procedures that 
address the potential for thermally decomposing the purge dam material 
during inert gas welding or post-weld heat treatment operations. 
Specifically, polyvinyl alcohol film manufactured by Chris-Craft Industries 
was the purge dam material used at these construction sites. The 
decomposition of this purge dam material at elevated temperatures causes the 
material to lose its solubility in water. As a result, the purge dam 
material cannot be completely dissolved during subsequent piping system 
flushing and cleaning operations. The failure of this material to completely 
dissolve could cause significant problems during reactor plant operation. 

Specimens of polyvinyl alcohol film were recently obtained from the Mono-Sol
Division of Chris-Craft Industries and tested at Franklin Research Center 
(FRC) to determine, among other things, the threshold temperature at which 
the material becomes insoluble in water. The results of this test program 
indicate that (1) the solubility of the purge dam material in water rapidly 
approaches zero if the material is heated and held at temperatures in excess
of 300F; (2) the purge dam material hardens and becomes difficult to 
break if subject to temperatures in the range of 300F to 400F, and
becomes brittle if heated to 450F; and (3) purge dam material heated 
above its threshold temperature is not soluble in commonly used laboratory 
solvents. The independent testing laboratory (FRC) therefore concludes that 
the Mono-Sol polyvinyl alcohol film will not dissolve during aqueous 
flushing of the system if the material has been heated to temperatures in 
excess of 300F. 

Recommended Actions for Holders of Operating Licenses and Construction 

It is recommended that all welding operations involving polyvinyl alcohol 
purge dam materials be governed by procedures that require the material to 
be located in areas that are sufficiently removed from heat so that the 
temperature of the material does not reach 300F. 

No written response to this information notice is required. If you require 
additional information with regard to this subject, please contact the 
appropriate NRC Regional Office. 

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