A large number of unexpected and sometimes rapid failures in potable water systems result from poor or faulty design, substandard materials and poor workmanship. This paper discusses typical failures and presents case histories due to substandard wall thickness, use of corrosive fluxes, erosion- corrosion, corrosion fatigue, improper reaming, excessive flux, overheating, cold bending, contact of pipe with structural members, missing, loose or improperly installed riser clamps, microbiological influenced corrosion due to inadequate cleaning and flushing, and faulty inspections.
Many copper potable water pipe failures in recirculating hot water systems result from localized corrosion pitting in areas where the water is soil and acidic, such as Vancouver, British Columbia. There are also many unexpected and sometimes rapid failures of copper water piping that result from design errors, materials and poor workmanship.
This paper discusses a number of case histories that relate to design errors, materials and poor workmanship. Examples include failures due to: corrosion fatigue, use of corrosive fluxes; excessive flux and solder; overheating; improper reaming, cleaning and fluxing; inflexible piping; cold bending; contact with building studs, etc.; substandard wall thickness; and microbiologically influenced corrosion (MIC) due to inadequate flushing and cleaning.
REFERENCE STANDARDS
There are a number of reference standards for the manufacture and assembly of copper potable water systems. They include:
- ASTM B 88 "Standard Specification for Seamless Copper Water Tube". This specification covers copper alloy USN No. C12200 Seamless Copper Water Tube, which is suitable for general plumbing requirements. The piping is supplied in nominal or standard sizes from 1A inch to 12 inch and in three wall thicknesses: K, L and M (Table 1).
- ASME B 16.22-1995 "Wrought Copper and Copper Alloys soldered Joint Pressure Fitting" and ASME B 16.18 "Cast Copper Alloy Solder Joint Pressure Fittings ". Fittings are manufactured to both of these specifications depending on whether they are wrought or cast. It is interesting to note that the minimum wall thickness requirement of wrought fittings is less than the minimum thickness of Type L or K piping (Table 2). Thus, the use of Type L or K piping is a false security since fittings and especially elbows are a weak link in the piping system.
- ASTM B 813 "Standard Specification for Liquid and Paste Fluxes for Soldering Applications of Copper and Copper Alloy Tube ". Fluxes covered under this specification are designed to be cold water-flushable and non-corrosive if properly flushed.
- ASTM B 732 "Standard Test Method for Evaluating the Corrosivity of Solder Fluxes for Copper Tubing Systems ". Corrosivity of fluxes can be evaluated using this specification.
- ASTM B 828 "Standard Practice for Making Capillary Joints by Soldering of Copper and Copper Alloy Tube and Fittings" and in "The Copper Tube Handbool(' published by the Copper Development Association. The procedures for making capillary solder joints on copper tube are described in these publications
PLUMBING CODES
The requirements for copper potable water piping are normally covered by Plumbing Codes. The British Columbia Plumbing Code requires Type L pipe as a minimum wall thickness and also requires larger nominal sizes for a given water flow rate than the Canadian Plumbing Code. These changes were brought about due to the more corrosive water encountered in British Columbia. The specification of Type L piping as a minimum is a false security in British Columbia since the fittings and especially elbows a
