Full penetration Weld and Weld symbol

Question from reader ----

"Whats a full penetration weld? And whats the welding symbol to use for a full penetration weldment?"Thanks.

Answer-----

This is a pretty common question and there is no way to answer it without some pictures.

Hopefully this page will shed some light on the subject.

A full or complete penetration weld can be a really thick weld that has been beveled and then penetrated by being filled with multiple weld passes, or it could be a sheet metal joint that is .020" thick and is penetrated without any need for a v groove bevel.

The weld symbols vary according to the type of joint.

Here is an example: lets use the example of a .120" butt joint. This could be a full penetration weld without any bevel.The weld symbol for a full penetration weld could look something like this.

It is full penetration because no depth of penetration is called for. That’s the rule. If no depth of penetration is called out, it is assumed that it is to be a full penetration weld.

Another example of a full penetration weld is this:

One last example is this partial penetration weld symbol

Notice that the 3/8 is not in parenthesis and the 1/2 is.

The 3/8 indicates depth of preparation or depth of the bevel. With the 1/2 being the depth of penetration requirement.

So there you have it… 2 examples of full penetration welds and 1 example of a partial penetration weld.

One thing to remember is Weld symbols are kind of complicated and take a while to grasp. And even then, if you don’t live in the weld symbol world and use them all the time, it is pretty easy to forget some things.

I have often seen that engineers leave off the dimensions when they really intend to spec out a partial penetration weld.

This can cause a lot of unnecessary time and money so if there is a doubt about a weld symbol and if you are working in a situation where you can question the engineers intent, it’s a good idea. Because once again, if the dimensions are left off, it’s automatically a full penetration weld.

One last picture that might help…here are some other groove weld symbols that are used to depict full penetration welds.