How can I detect pipeline cracks using OpenCV and Python?
Try this:


Don't convert the image to grayscale, instead convert to HSV
Then, by changing the range of H,S and V, try to mask the crack (using a trackbar can be very helpful) 


For example:

lower_value_blue = np.array([80,106,5])    # creating a range of HSV colours
higher_value_blue = np.array([150,255,150])
mask1 = cv2.inRange(blur1,lower_value_blue,higher_value_blue)


This one mask blue colour, without using trackbar

Hope you will get the result