Plastic Failure Analysis: Fusion Welded HDPE

Poor Welding of a Carrier
Pipe Joint There was no
 Melting on a part of the joint

Read Consulting, a California failure analysis lab, has performed numerous plastic failure analysis on various types of plastic pipe. This includes PVC, CPVC, Delrin and Polypropylene. In this case a plastic failure analysis was performed on a failed containment waste transition line made with fusion welded high density polyethylene pipe. The line was several miles long. The interior transmission pipe had an OD of 8 3/8" and a 1/2" wall thickness.  The containment pipe had  12 3/8" OD with a wall thickness of 1". There were numerous leaks in the line,  and all were found to result from poor fusion welding procedures. The upper right photograph shows a weld on the interior carrier pipe that leaked. In this case the ends of the pipe had not been properly welded before the pipes were fused. This resulted because the pipe end never contacted the heater plate. Obviously, the fusion weld procedures were not properly followed.  It is important to follow exactly the manufacturer's recommended procedures when fusion welding high density polyethylene pipe. In addition, all joints should be leak checked before being buried in the ground. Poor fusion welding creates leaks that are hard to find and are very expensive to remedy. 

Glass Expert Performs Failure Analy on Low E Windows

California failure analysis lab was asked to determine why windows in an expensive hilltop home failed. The windows in question were Lo- E windows that were tinted to absorb infra-red light. At this location two south facing, side-by-side windows cracked. The window expert at Read Consulting was asked to perform a glass failure analysis to determine the root cause of the failure. For this failure analysis the site of the origin was cut from the window and  the failure origin was examined using a low power optical microscope. Both windows failed in an identical manner. Thermal expansion of the center of the Low-E window put the ground glass window edges in tension.A damage site from either the window sizing or window seaming processes was activated by the thermally generated stresses and cracked these windows. Please refer to the photographs above.    

Tempered Glass Expert Performs Failure Analysis

California Failure Analysis Lab routinely performs tempered glass failure analysis. In this case the glass expert determined that the tempered glass failed as a result of a pointed object that created crush damage that penetrated the compressive layer of the tempered glass. The glass was a large piece  10 mm thick. Thus, the compressive layer is approximately 2 mm thick on each face. It is interesting to see how the failure initiates on the surface and progresses inward. Later the residual tensile stress causes the entire glass panel to break into small "cubes". On the face of the panel there is a glass crush point.

Porcelain Failure Analysis

California failure analysis lab is able to show similarities between glass failure analysis and porcelain failure analysis. The predominant tool for tracking a crack in glass is to look at "Wallner lines" These can tell the direction of travel of a crack in glass. This allows the glass failure expert to trace the crack back to the origin. He can then analyze the origin microscopically to determine the root cause of the failure. Glass is a smooth material, and the Wallner lines are readily visible. Porcelain is also a brittle material, and it also fails in a brittle manner. The difference is that the porcelain fracture surface is grainy and artifacts on the porcelain fracture surface (such as Wallner lines) are very difficult to see. Above are photographs of the fracture surfaces of two bending failures, one glass and one porcelain. The Wallner lines on the glass fracture surface are obvious and readily visible. The Wallner lines on the porcelain surface are very difficult to see and are best seen in oblique light. A sample of each is given above for the reader to see the differences/

Glass Expert Discusses Bend Test Fracture Surface

 California Failure Analysis lab performed a compound bend test to determine if the failure surface can be at an angle to the surface. One curious result was a curved fracture surface. This occurs when the clamp on the topside (i.e. tensile side) was behind the support underneath. If the two clamped sides are aligned, the crack is perpendicular to the sample face This information is useful when analyzing failures of other brittle materials such as ceramics (i.e. ceramic failure analysis).

Rubber Failure Analysis: Inner Tube Failure

 California failure analysis lab performs rubber failure analysis on a failed bicycle inner tube. The rider was braking while descending a long steep hill. Toward the bottom of the hill his inner tube failed, and he heard a loud pop. The wheel rim was too hot to touch. A failure analysis was performed and the failure originated at a point on the tube that would have been in contact with a spoke "nut". It is believed that the tube was heated to the highest temperature at this location, and it softened to the point of failure. In addition, the tire pressure was elevated due to the heating of the rim from the friction of the brake pads. Upper right is a 40X photo-micro graph of the failure origin.

California Failure Anal

California Failure Analysis lab performed an electronic failure analysis on Pogo pin spring loaded contacts (Pogo connector pins) to determine the cause of intermittent open circuits. Electronic testing had detected that there were times when the spring loaded pin was depressed, the circuit would open and there would be an interruption of the signal. The cross section of a single Pogo (upper left) showed that the  the structure was entirely made of gold plated parts (pin, spring and outer
 case).  However, there was some concern that the inner wall of the case
was defective. For additional failure analysis, a sample case was split open (photo-micrograph on the right) and the inner surface was found to have horizontal machining marks,  not be plated, to be corroded and contaminated with plating salts. These plating defects indicate that the intermittent contact problem will worsen with time. These results are not surprising since the case is really a deep blind hole, and this makes it impossible to properly clean and plate  the interior. The vendor being analyzed is an overseas vendor that was to replace a reliable US supplier. These parts are unusable.

Rubber Failure Analysis: Rubber Seal Failure Analysis

A California failure expert witness was asked to determine the root cause of a rubber gasket leak. 

The molded rubber gasket seal was integrated into a hydraulic lift operating at 650 psi. Over time it had developed a very small hole and approximately 60 gallons of hydraulic oil escaped through this small leak. Read Consulting Failure Analysis Lab was asked to perform a detailed failure analysis to determine the cause of the leak.  The subject rubber seal failed as a result of a rubber molding defect. During the molding operation there was a region where the flowing rubber failed to re-bond properly. Over time the high pressure (650 psi) hydraulic oil created a hole in the weakened rubber and this resulted into a rubber failure and a hydraulic leak. Upper left is a 30X  photo-micrograph of the pinhole leak. The leak "protrudes" outward showing that the failure was created as a result of the hydraulic pressure. 

Device Patent Dispute: Automobile Rear View Mirrors

Read Consulting, a California failure analysis laboratory, often becomes involved with device patent disputes. In this case a patent dispute focused on external automobile rear view mirrors that had integral flashers showing through openings in the mirror. The assembly consisted of an array of LED lights that were behind the mirror, and these flashed through holes etched in the thin film chromium front surface mirror. Read Consulting had the electronic device expertise and thin film expertise to understand the various elements of the patent and to render an opinion in the patent dispute. Curiously, the same equipment that is used to perform failure analysis is also useful for examining elements in a patent dispute.

Construction Defect Analysis, Window Damage

California Failure Analysis Expert Witness performs a glass failure analysis on defective tempered glass windows installed in a public building. One of the construction defects was window scratching. Representative windows were removed and sent to the Read Consulting California failure analysis lab. This allowed a detailed investigation of the window defects. The failure analysis determined that the scratches were caused by post construction cleaning. Upper left is a macrophotograph of a typical set of scratches. Their parallel nature shows them to have been caused by a metal scraper. Upper right is a 40X photomicrograph of a scratched region. These scratches were in the glass. There was no coating on the scratched surface.