Preservation of Weld Fractures for Evidence Evaluation

TASA ID: 1850

1. Initial Discovery of Fracture

Sometimes when a weld fractures, it may result in personal injury, property damage or even a fatality. If litigation is the result of a weld fracture, it is important to retain and preserve the weld and the fractured weld surfaces for evaluation by the experts.

Preserving the weld fracture in pristine condition for the expert’s review is important and efforts should be made to not damage the weld fracture surfaces. The weld fracture surface and surrounding area will be indicative of the type of fracture and will also show if there are internal defects or voids that may have been a contributing factor to the weld failure.

2. Improper Handling of Weld Fracture

Evaluation of the weld failure is first acquired optically with microscopy; therefore, it is important that the failure be preserved as much as possible.

Many welds have similar types of common defects typically caused by operator error; however some welding processes yield different types of distinctive defects. Isolating those defects may be the key to uncovering the possible root causes and/or contributing factors of the weld failure.

The initial reaction by some, is to try and reassemble the opposing halves of the fractured weld. This should be prevented, as trying to reassemble the weld fracture will sometimes deform those surfaces and remove important information that is needed in determining the cause of the weld failure.

One should deter any efforts to clean by removing particles; probe or insert other metallic or non-metallic objects, such as screw drivers, knives, pens, pliers, etc. in an effort to open the weld fracture wider to obtain a better view of the fractured surface. This sometimes results in key surface features being removed that are critical in evaluating the evidence.

In some materials, such as stainless steel, it is important that the weld fractures be handled with the use of rubber gloves to prevent oils and acids from the skin contaminating the surfaces.

3. Proper Handling of a Weld Fracture

The following is a condensed version of a weld failure analysis that represents the importance of preserving the fracture surface for evidentiary evaluation. It involved a stainless steel rotating shaft that was welded. The specifications involved an explicit welding process to join two mating parts. Under a cyclic load the shaft fractured after being in service for 18 months.

Figure 1 is the surface of a fractured stainless steel shaft. The owner’s specification mandated that this rotating shaft was to be welded using a specific welding process known as Gas Metal Arc Welding (GMAW).

The location of the yellow arrow shown below is the fractured surface and the red arrow in Figure 1 corresponds to the red arrow in Figure 2.

Figure 1
Fractured Stainless Steel Shaft (100X)

Upon further evaluation at a higher magnification, Figure 2 shows particles that were bonded to the fractured surface within the fracture interface.

Figure 2
Particles Found on Surface (100X)

Using an analytical method of testing known as Energy Dispersive Analysis by X-ray (EDAX), revealed the presence of Tungsten (W), as shown below in Figure 3.

These Tungsten particles were present within the weld as the result of using the non-approved welding process known as Gas Tungsten Arc Welding (GTAW). This non-approved welding process was used to “tack” the shaft in position prior to the commencement of the final weld.

Figure 3
Energy Dispersive Analysis by X-ray

As a result of these high density Tungsten particles being introduced into the weld, they initiated cracking in and around the fracture nucleation site as shown in Figure 4. It was determined that the Tungsten inclusions were the ultimate cause of the failure.

Figure 4
Cracking within Weld Area (400X)

This is a good example of obtaining and preserving a weld fracture in pristine condition.

If the weld fracture was improperly handled, the possibility of the particles being removed from the surface increases, and it may not have been revealed that the incorrect welding process was used.

4. Conclusions:

1.    Preserve the weld fractured surfaces in pristine condition, if possible.

2.    Isolate opposing fracture surfaces and prevent them from coming into contact with each other or other materials.

3.    Keep in a low humidity, constant temperature and controlled environment, if possible to prevent surface oxidation.

4.    Contact an expert to perform an evaluation as quickly as possible after the weld fracture occurs.

This article discusses issues of general interest and does not give any specific legal or business advice pertaining to any specific circumstances.  Before acting upon any of its information, you should obtain appropriate advice from a lawyer or other qualified professional.

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