How Failure Analysis Uses Data to Enhance PQI Test Plans for Electrical Relays
April 13, 2022
In all electronic and electromechanical applications including manufacturing systems, commercial equipment and retail products—relays play an important role in regulating current and signal flow throughout system circuitry. These components can fail for a number of reasons including manufacturer defect, impact during shipping, improper installation, etc.
There are specific types of relays that fail more often than others, which can cause costly workflow disruptions and downtime at a rate that is unsustainable. This is why Constellation PowerLabs’ PQI (Parts Quality Initiative) program is highly valuable to power generation and manufacturing facilities who want to stay ahead of the competitive curve. The proprietary PQI test templates are continually updated with component testing data gathered by the Failure Analysis Services department. When a new failure mode is identified in a PQI tested part, that failure mode critical characteristic is added to the PQI test template.
Constellation’s PQI program has been amassing electronic and mechanical instrument, component and equipment failure data since 2006. This information is stored in a proprietary database called OneLab, which can be accessed via subscription by industry professionals who need to know the performance profiles of frequently used critical components.
Recently, information in the PQI database concerning a frequently used electrical component was updated after Failure Analysis Services conducted a thorough inspection of a popular anti-pump relay. Through these findings, a more thorough PQI test plan for this specific piece of equipment was updated. Subsequently, this provided OneLabs subscribers with a deeper level of security against installing a faulty part and interrupting facility production.
A Connectivity Issue
A relay which was functioning as a component of a breaker had failed and was presented to PowerLabs for laboratory analysis. The failure analysis team began with an as-received inspection and photo documentation. Visual examination revealed one of the braided wire ferrules had become detached from the brass contact strip at the resistance spot weld. There were no indications of thermal or electrical damage.
Taking a Closer Look
Further examination of the detached weld was conducted by first removing and examining both brass contact strips. It was noted that the indentation (created by the welding electrode) on the brass contact strip with the detached weld was smaller in diameter and potentially shallower than the indentation on the brass contact strip with the intact weld. Additionally, it was observed that the indentation on the contact strip with the detached weld did not have concentric circles like the intact weld.
Comparison of Heat Signatures
It was further noted that the detached weld between the braided wire ferrule and the contact strip displayed little to no evidence of heat or fusion. Yet the relay was most likely still in operation due to mechanical friction provided by the indentation from the welding electrode. Over time, handling and operation most likely caused complete detachment of the connection. Meanwhile, the other connection clearly displayed signs of heat and fusion at the connection point of the braided wire ferrule and the brass contact strip, specifically evidenced by reconstituted brass material beneath the ferrule. A tug test concluded that this connection was still intact.
A Deeper Investigation
Lastly, a chemical analysis of the relay parts in question was conducted via Energy Dispersive Spectroscopy (EDS). It was discovered that no significant discrepancies in chemistry were present which would have caused an unsatisfactory weld. The contact strips, the ferrules, and the braided wires were consistent with brass, nickel plated brass, and tin-plated copper, respectively.
How Failure Analysis Uses Data
The Failure Analysis Services team concluded that this electrical relay component failed due to a manufacturing defect at one of the two resistance spot weld connections located between the braided wire ferrules and the brass contact strip. The failed side displayed little to no signs of heat or fusion, thus indicating a system flaw in the soldering (spot welding) stage of the product assembly process. This was further evidenced by the fact that the weld process on the failed connection side created only an indentation which resulted in a temporary, friction-based connection that was loosened and disabled by routine handling and operation.
From this data, PQI test plans for electrical relays was updated assure the weld/solder connections are inspected by performing a visual examination of the resistance weld connection and/or a light pull test.
Valuable Subscriber OneLab PQI Data
This information was then imparted to the client and uploaded into the OneLab PQI database. This update is of profound value to OneLab PQI subscribers who use this particular component, especially in large quantities.
Subscribers to this proprietary, PQI members only database, can view the failure rate data of this individual component. While test reports are only available to the facility that initiated the failure analysis, reports may be shared if your company makes a request to their customer care specialist. If the other party agrees to sharing of the test report, the customer care specialist can relay that information that contains crucial details of the failure.
With this captured data, it shows the critical importance of testing this piece of equipment before putting it into the component inventory. Specifically, the braided wire ferrule spot weld connections to the brass contact strips should be subjected to a simple tug test before approving the part for service. As a result of this failure, the updated PQI test plan can and will methodically ensure this test is performed and save untold amounts of lost mechanical hours due to downtime caused by failed connections in this specific part—a commonly used electrical relay.