i decided to do some research and it was the combination of the uv rays, and me scraping my edges on it.
heres what i found
The exposure of PVC to the UV component of sunlight causes PVC molecules in the first .001" to .002" of exposed surface to become permanently converted to a complex structure typified by polyene formations. The result is a brownish discoloration, often called "UV discoloration", "UV degradation", or more commonly "sunburned". UV discoloration does not occur where PVC is not exposed to sunlight, and ceases when exposure ends.
The discoloration process is time-dependent, and can be slowed with the addition of UV absorbers in the PVC compound. The most common additive used for this purpose is titanium dioxide, which also functions as a pigment.
Research has been done to determine the effects of long-term (two year) sunlight exposure on PVC pipe (see "UNITR-5: The Effects of Ultraviolet Aging on PVC Pipe", by the Uni-Bell PVC Pipe Association.) Other than visible discoloration, the following summarizes the results on pipe physical properties:
Physical Property Performance Characterstic Effect of Sunlight Exposure
Impact Strength Impact Resistance Decrease
Tensile Strength Pressure Capacity No Effect
Modulus of Elasticity Pipe Stiffness No Effect