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Rubber liner failure diagnosis and probable causes. Part 1

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Figuring out just what went wrong after the fact is difficult but some of the circumstances of the failure can indicate the modes of failure.

Below I will list the problem and then identify what can go wrong in the lining procedure, manufacturing of rubber, improper match of material to process and mechanical failure that may have created this situation.

 

Delamination at the edge and or seam only: This occurrence can happen for a few different reasons.

Sharp Internal Edges :The most common reason is improper steel prep, meaning the welded flange had a sharp internal corner. Due to the rubber elasticity it’s difficult to properly adhere to an inside sharp corner.  During the cure the rubber may pull itself out of the corner depending on the rubber type. This results in a potential air pocket which can cause failures in the cure and is susceptible to erosion or edge separation depending on the compound.

Chlorobutyls and Bromobutyls and slurry chemicals: An interesting fact about rubber sheet with butyls is that on often rubber sheet manufacturers will us what is called a tie gum rubber to promote adhesion as a small layer. Depending on the application the tie gum which is a pure natural rubber may not be able to handle the high heat or the chemicals butyls are renown for. Separation at the seam is common if closed skives aren’t used or if the temperature exceeds the natural rubber threshold

 

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Edge delamination due to tie gum backing.

 

Sheet or sections fall off or are peeling off with little effort:

Improper Sandblast or dirty surfaceA blast profile of Nace standard SSPC SP5 is required with a profile of 2-3 1/2mils for raw rubber and a profile of 4 mils for pre-cured rubber . The reality is that the adhesive systems used in rubber lining are very aggressive and the blast profile can range and still be successful. None the less if you do not use proper girt to blast. Accidentally blasted with glass bead you can have failures.

Problematic adhesive: If you don’t stir the adhesive well, you will be applying more solvent than adhesive. If you  get dust on the adhesive you will prevent proper adhesion between coats or sheet. This will likely cause failures in the cure but if it makes out is prone to delamination in the field.

 

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Example of improper adhesive causing the sheet to delaminate.

 

Rubber edges growing like mushrooms, or failures near the edges:

UV and Ozone: UV and ground level ozone are rubbers enemy. Liners exposed for a period of time to the sun are prone to failure. Most rubber loose their elasticity and ability to combat erosion and corrosion. The outer edge is susceptible as it  most likely to be exposed to the sun. Although flange connections exposure have no performance effect as the inside of the rubber is not being exposed. Spools stored on the ground are likely to have exposure problems. Most rubber likes dark spaces and generally wont be affected by light in the short term like a few weeks. As a rule of thumb keep all rubber capped or cover.

 

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UV exposed rubber.

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Edge failure de to exposed rubber to UV.

 

Bubbles and dark spots in the rubber: 

Bubbles can form for various reasons. They will be discovered during the curing process. If not inspected and repaired before going into service will be a cause for concern long term. The rubber will be susceptible to tear and will wear as it will create turbulence.

Rubber calenderer with bubbles: This is very common as the rubber is layered up, air can be trapped between layers. The result is unsightly bubbles in the sub-straight. If the bubble are not very pronounced it will not affect performance. A visual inspection and a spark test can determine the severity of the bubbles.

Bad stitching and trapped gasses: If the rubber is improperly stitched or there is problem with the off gassing of the adhesive you will find out in the cure. Bubbles will be the result.

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An example of bubbles calendared into a sheet.

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An example of bad stitching, diluted adhesive or poorly applied adhesive, trapped gasses or dirt on the sub straight or liner.

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This is an example of rubber that has impurities in the compound which reacted to the cure.

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Example of sheet that has been calendared with trapped air. This is a bad liner and can cause turbulence, this would not pass a spark test and would perform poorly. This liner cannot be used!

 

Pre-Mature Erosion of the liner:

The factors which cause a liner to wear quickly  are vast. More often than not the velocities and particle sizes have exceeded the limits of rubber sheet. Chemicals not conducive to the rubber liner may be present and may have affected the liner such as pine oil a hydrocarbon which is not friendly to rubber.

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This piece eroded in less than a week. Velocities were extremely high and the particle size was 3/4″ minus. Very large. A better application would have been ceramics or chromium carbide.

 To be continued….

 

 

Dan Chamberland

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