How to fix oil burner pipe ?

first lets start with why your pipe cracks very easily ? do you heat it properly?

the quality of the glass pipe, many glass pipe are made from cheap materials, the glass tub wall are very thin  and for the bowls are much thinner then the tube, because when you blow the glass, it get bigger thinner bowl. 

second the heat you apply to the glass pipe, most people use it just turn the lighter or torch  up all the way max burns, sometime the glass will break instantly,  so the correct way is apply the heat slowly, so the glass gradually warm up. 

so basically just try lowering the flame, the object is to heat the product not burn it, don't touch the glass with the flame. And don't heat any other part of the bubble except for the bottom. That is the thickest part of the pipe.

Turn the pipe evenly. Let the pipe do the work, not the lighter. Try to get the product to re-crystallize on the bottom of the bowl, not stick to the sides, that way you only heat the very bottom.

If it breaks during a cleaning...try this: I put my utensil in a plastic cup of hot water with bleach and dawn soap, making sure the stem is completely submerged. Heat it in the microwave for 3-5 minutes, cool it, let air dry and then it should be good as new.

I like to rinse my pipe in plain hot tap water 1st before I do the microwave cleaning. do not put a hot pipe into a cold water, it will break instantly. 

Clean pipe before each load and Do not torch or bic lighter clean it. That wears down the glass too fast and it stinks too. Soaking it is better

Try loading smaller bowls. Larger bowls require more heat to melt, potentially causing the pipe to crack. It's better to start small and work your way up, I've found. Give it a good minute or two between hits.

Clean the outside gently after each hit with a soft cloth. I like shop rags myself, and you don't need to wipe it hard. Also, do not put your fingerprints on the glass, our prints are oily. It will ruin the bowl’s integrity.

so overall, if you get cheap glass pipe, may as well get it from different vendor next time, and when you buying it check the glass wall thickness. the thicker the better. 

Smoking Harms, stop smoking if you can.