FLEXIBLE GAS CONNECTOR, SOLDER JOINT FAILURES
Charles C. Roberts, Jr.
Periodically, an explosion loss occurs that is related to the flexible gas connector
used to transport fuel gas to various appliances (Claims, September 1988). A unique
failure of the brass flexible connector has been observed involving the solder joint near
the flare/threaded nut end. Figure 1 is a cross-sectional view of an old flexible connector
design where the corrugated flexible brass tubing is soldered to the end flare. The end
flare is the mating surface with the appliance fitting and is secured by the threaded nut.
Apparently, over time, the solder joint fails and a crack forms at the solder/brass
interface. Newer connectors do not have this reliability problem.
Figure 2 is a cross-section of the more modern connector with a flare that is formed as an
integral part of the connector. The absence of the solder joint enhances flexible connector reliability.
Figures 3 and 4 show two different solder joint connectors that failed
causing an accumulation of natural gas in a home and an explosion. The
characteristic solder fracture surface is apparent in each of the connectors. The
flexible connectors showed little sign of excessive bending or strain. In each case
the connectors were over 30 years old.
Figure 5 is a photograph of a modern flexible connector with a protective
coating. Figure 6 is an end view of the integral flare. Figure 7 is a view of the
manufacturer identification band.
The apparent cause of the failures is an aging effect, characteristic of
solders. Solders are multi-phase lead/tin alloys, which tend to precipitate over
time, causing a reduction in fatigue strength. As a result of cyclic loading brought
on by periodic forces such as thermal expansion and contraction of the solder
joint, metal fatigue initiates a crack that eventually propagates through the solder
joint causing the gas leak and possible fire or explosion.
When analyzing an explosion or fire, which is a result of a gas leak in a
flexible connector, determine if the manufacturing method involves a solder joint.
If a fractured solder joint is found, then metallurgical analyses (Claims Magazine,
April 1989) may be required to verify the failure mode. The age related failure of
the old solder joint technology is tantamount to a "time bomb" in that it can occur
without warning and at virtually any time.
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