I do only web development works on my desktop ubuntu 16.04. I have a Cheap Nvidia external graphics card with it. It works fine but sometime computer gets hang on long run. So I wonder if i remove Nvidia external graphics card and use motherboards Intel built-in graphics then this can be solution? Is ubuntu more stable with Intel built-in graphics? Since Nvidia doesn't provides any driver for ubuntu?
Some important informations to give when asking this are the processor's model and the video card's model. If the processor is too old, it may suffer alone when using Ubuntu's Unity.
My friend had issues when using Ubuntu with a Nvidia GTX 550 Ti. The computer would freeze after some time. Lower time when using Ubuntu, higher time using Lubuntu, then we installed psensor and we checked that the problem was a overheat.
There are possible ways to keep using the Nvidia card: you can configure nouveau's (the open-source driver) to set to a fixed fan speed. Configuring nouveau is not very simple, but it is doable. If the video card is noisy, this may be annoying, but the hangs will stop.
Nvidia provides drivers to Ubuntu, however those aren't open-source. If you mind with using only open-source programs, this may be not acceptable. If you don't mind using closed source programs, you can install it. They are called nvidia-3XX, with the "XX" being a number version, which depends on which model your video card is to choose correctly. The Nvidia driver comes with a interface that can easily change fan speed and can (this is a possibility only) automatically control the fan.
Now, if you want to use Intel on-board video card: on my experiences, it's the most stable one of all graphic implementation I have ever seen. Ever. Linux graphics is a big project, which is heavily supported. Intel Graphics's support for Linux is even better than the support for Windows. I have a 2003 notebook, a 2011 desktop and a 2016 notebook, the three with Intel Graphics on Linux, and the three work really well. The 2003 notebook don't work with Windows 7, as a comparison.
So yes: Intel graphics are more stable. If you need the performance, then I would recommend to install the correct Nvidia driver for your specific video card.