Failure on a fiberglass pipe

The goal of the investigation is to characterize the material and understand the causes of the damage occured on a fiberglass pipe.
Not damaged Area
Damaged Area
The pipe under investigation consists of three parts: inner liner, structural wall and external liner. The following photo shows the transversal section of the pipe sample.
FT-IR Spectrum
The FT-IR analysis was carried out on the material "as received". The resulting spectrum shows that the sample results to be made of a thermosetting resin-based phtalic.

TGA Analysis
The TGA analysis was carried out on the as received material for each area examined (damaged and not damaged).

DSC Analysis
From DSC analysis carried out on the two areas examined, the thermal behaviour of both is the same. In all the two areas analyzed (damaged and undamaged), there are no signs of lack of cross-linking of the thermosetting resin used.

Filler Analysis
A share of the two areas under investigation were subject to calcination in the oven at 700°C for about 60 minutes. The ash content obtained is shown in the photos below.

Moreover, the ashes of the sample under investigation were subject to further qualitative analysis through SEM/EDS microanalysis. The composition results to be made of oxygen (O), alluminium (Al), silicon (Si) and calcium (Ca).
The ash content: not damaged area - The ash content: damaged area
The following photos show the glassfiber examinated on the two areas through the SEM. The diameters of the glassfiber observed were measured.
SEM: not damaged area - SEM: damaged area
The residues found on the surface of the tested item were analyzed by electron microscopy SEM (see the spectrum below).The resulting composition is made of oxygen (O), alluminium (Al), silicon (Si), magnesium (Mg) and traces of calcium (Ca), sodium (Na) and chloride (Cl). From the composition found, the surface residues are made of fiberglass remnants and traces of salt from sea water (where the item under investigation was immersed).
EDS Spectrum
Failure Analysis

The photos below are relevant to the damage conditions of the item examined.

The first damage found on the surface of the item examinated is characterized primarily by a significant removal of the surface layer (see the photo No.1).

The observations made on the damaged surface shows craters of different sizes, which suggest the bubbles (see the photo No.2).

Regarding the trasversal section of the damaged area in question it shows significant empties in the material. These defects are not present in the trasversal section belonging to the undamaged area (see the photo No.3).

Furthermore, the inorganic residue obtained by calcining the damaged cross-section, consists in layers of glass fiber (arranged at random and not random).

The cross section of the damaged area shows significant defects of integrity of the material; these defects are not present in the cross section of the undamaged area (see the photo No.4).
Conclusion

From chemical investigations performed on the two areas examined (damaged and undamaged) there was no evidence of significant differences. But as regards the structural surveys of both areas examined, they show a significant difference. The damaged area is characterized by empties in the material, due to a lack of compactness of the structural layer.

This lack of structural compactness of the structural wall  is probably due to a lack of resin, as it is confirmed by the increased total content of fibers found on the damaged area.
In addition, the round shape found on empty planes of fiber analyzed, suggests that empties are caused by gas developments.

The development of gas is confirmed by the defects found on the surface of damaged areas (defects are attributable to gas bubbles).

For a fiberglass items, is a characteristic degenerative phenomenon known as "osmosis".
Osmosis is a physical-chemical phenomenon consisting in the passage of a solvent, in our case the water through a membrane separating two liquids of different salt concentration. In fact, the fiberglass tube immersed in water is the first condition to follow osmosis. The second condition is that within the laminated fiberglass are trapped air bubbles more or less close to the contact surface of the gel coat (external liner).

First, the water passes through the gel coat (external liner) and then goes to fill the bubbles found in the structural wall. Subsequently, the water inside the bubble starts to melt everything that finds soluble. Then, this concentrated solution draws water from outside through the gel coat, after which the pressure in the bubble increases until it forms the bladder.

The phenomenon of osmosis is a degenerative process. Cases may be:
  • Low quality gel-coat (external liner), for example a little waterproof resin
  • Working inaccurate for the presence of air bubbles in the stratified
  • Excess catalyst used during the stratification.
  • Stratification carried out in too cold or too wet ambient
  • Presence impurities or soluble in glass or resin.
Emma Martin Gonzales - specialist in testing polymers
Sigla.com - Internet Partner