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September 13, 2016
Composite Repairs Part 1 | What are the effects of installation pressure on composite repairs?

Posted by: Casey Whalen

Composite repairs installed at operating pressure will do two things:

1. Protect the pipe from future external damage (corrosion or mechanical).

2. Reinforce hoop stress in the event of pressure spikes or continued wall loss (internal).

Composite repairs installed below operating pressure will, in addition to the above:

3. Immediately begin reducing the hoop stress experienced by the pipe wall, which could be crucial in lines that see heavy cycling.

To explain this effectively, there are a few key points in composite repair theory that need to be spelled out first. Some are relatively basic, but nonetheless vital in setting the stage. Keep in mind the following formula, solving for “Hoop Stress”:

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Where ‘P’ is the internal pressure, ‘D’ is the pipe diameter and ‘t’ is the pipe wall thickness.

KEY POINT #1: Pressure in a pipe is converted into hoop stress, which is distributed throughout the thickness of the pipe.

KEY POINT #2: As the thickness of the pipe wall decreases due to external defects, the hoop stress in the remaining thickness increases.

KEY POINT #3: A composite repair works (for hoop stress problems) by alleviating the hoop stress seen in the pipe wall. It does this by absorbing hoop stress within the composite fibers.

Follow our latest blog series as we address how hoop stress can be absorbed and how composite repairs can alleviate issues. Contact our engineering team for more information.

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Category: Pipe Wrap

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