My car is 99 Corolla, gas tank rusted from inside and not worth repairs, after getting one decent used tank in Siang Gong Soi I tried to get the fuel tank off( I've replaced tank in similar Corolla ), after years of aging and use, this Corolla's fuel line threads( similar to "FUEL LINES" pointed in the attached pic ) really doesn't want come off, wrench, vise grip, extension bar, everything failed to loosen them. I dare not heat up the fuel line, also these 8mm or 5/16" whatever piping are indeed very fragile. 

 

I cut off the fuel line to get the rusted leaking tank off, now I could use my 1/2 IR impact driver, even this tool couldn't bust them in half-setting, set to full torque and finally got the threading off, found there isn't any painting nor glue nor sealing as I suspected, just nasty oil residues.

 

Wonder if there's proper way to deal like this situation? 

 

Now have to make my new fuel line... I have pipe bender and taper presser for the work, wonder where could I buy some 2m length fuel pipe, Vorajak perhaps? 

 

 

 Fuel lines in the picture generally don't come off they are part of the fuel pump assembly

I mean this connection... due to failed attempts by vise grip and air wrench, loosen torque is well above 250 Nm, granted

 

Seems very common issue, I remember my last success with a different Corolla is by two vise grips and two steel tubing

It may looks a harmless 1/2" thread, but as firm as one 32mm castle nut of wheel bearing! 

You will have to heat the flare nut. Years of exposure to road dirt has packed the space between the inside of the flare nut and the steel tubing with fine sediment. Remove the in tank fuel pump assembly, blow dry it and Blow the fuel line clear of fuel first. No danger of explosion as it is not in a confined space, but keep a fire extinguisher close by. Heat flare nut, let cool, WD40 the threads while in a vertical position, allow to penetrate, flare nut wrench, open end wrench and a quick smack and you are done. When reassembled, pack the space with silicone to stop crud getting in, coat threads with NeverSeez and it will come off easy next time.

Thank you very much! 

As I feared, heat up is easier solution. And thanks for the reassemble suggestion! 

Bottle of nail polish remover from 7-Eleven. Mix 50/50 with ATF. Makes good penetration oil.

Works for decades with old rusty threads: break fluid. Pour some on and let it soak for a while. 

Easy really,just use 2 light hammers and hit the opposite sides of the female nut at the same time,this mishappens the nut enough to loosen it,spraying with wd 40 will help as well..

Fabricating new gas line

 

Following some careful prep I'm able to double flare stainless tubing painless with cheap tools.

 

Mesa very happi!  a lot of oiling really helped the tool to hold up against stainless steel( easy to work harden, difficult to anneal )

 

8mm OD x 6mm ID x 3m length tubing 1500 baht, @ klong thom ( shop name Bangkok Salamphan ), new line used 2.10m

 

Loctite Nickel Anti-Seize 1 pound 1400 baht @ klong thom ( shop name Siam Trade Machines ) expensive