Google dictionary defines tensile strength as "the resistance of a material to breaking under tension."

Part of the formula for reading a welding rod symbol has to do with tensile strength. The first two digits on the rods number represent it tensile strength. "For example the number '70' in an E7018 electrode (rod) indicates that the electrode will produce a weld bead with a minimum tensile strength of 70,00 psi." -miller welding

In order to become a Certified Welder, you must past a number of tests. This is common practice for a number of professional fields. The test that a welder must perform is measured by strength. Bend tests, pull tests, x-ray tests, pressure tests. Will the test stand up to or withstand the pressure? The key to a successful test is a good root pass. That is the first weld in a joint that joins two metals together. If this is not solid, has impurities, or gaps, no matter what type of welds you put on top of that it will fail the test.  How do you know your test failed? It breaks. If you can get that root in good, a good foundation, your test has an above average shot of passing. After you put the root pass, you proceed to fill the joint with multiple welds until the joint is filled. There are different processes to achieving success. Some weave, some run stringer beads, and both have passed.

Think about life as believers in Jesus Christ, we too continually have to take tests. Some are bend tests, pull tests, pressure tests. 2 Corinthians 4:8-12 says "we are hard-pressed on every side, yet not crushed; we are perplexed, but not in despair; persecuted, but not forsaken; struck down, but not destroyed- always carrying about in the body the dying of the Lord Jesus, that the life of Jesus also may be manifested in our body. For we who live are always delivered to death for Jesus' sake, that the life of Jesus also may be manifested in our mortal flesh. So then death is working in us, but life in you." What types of tests have you faced recently? We daily face tests. From the person cutting us off in traffic, the unfriendly person at the office, or the blazing hot summer sun that you may have to work in. All of these are tests each day. Over time you will increase your tensile strength to support any test you go through. But the key is the root, your foundation. If you lay a clean solid foundation on the Word of God, stand on the Spiritual Principles spoken of, we too can pass the test when it comes. 

For most structural builds the use of E7018 is common. For pipeline welding the E80xx is common. For the non critical welding E60xx is the rod of choice. 

So the most important question is, What are you building? Better yet, what does God want to build in and through you? If you are just starting out like the guy just learning to weld you probably won't need more than an E60xx rod. Get acquainted with that then He can build something that requires more strength and experience. We move from faith to faith, glory to glory. Build your tensile strength in the Word of God!