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Up Topic Welding Industry / Technical Discussions / "Penetration" or "Fusion"?
- - By Stephan (***) Date 03-18-2007 13:41
Dear Colleagues,

at the danger you may lough on me when I am asking the following.

Can anyone of you kindly explain to me the difference between "Penetration" and "Fusion" ?

Due to the very interesting topic of Shane Feder just shortly ago and the excellent explanations of Gerald "CWI555" I guess that I have misunderstood and further made something wrong when I have discussed sometimes to fellows in the past, and have used the term "depth of penetration" for expressing the depth the weld metal has "fused" the base-material.

From the explanations of Gerald I mean to have understood that the "Depth of Penetration"(?) is not equal the "Depth of Fusion"(?) in the US-Standardization. Is that true or have I misunderstood something totally wrong.

Background of the question is - of course - the topic of Shane but also the fact that within the German/European Standardization (at least as far I know) is no difference to find between "fusion" or "penetration". In Germany we use the term "Einbrand" what approximately means how "deep" the arc has "penetrated" into the base metal and which is indirectly a "gauge" for where the fusion line can be located.

Thanks in advance to those one who will kindly show me the way!

Parent - By 803056 (*****) Date 03-18-2007 18:03
One way to explain the difference is to look in AWS A3.0 Terms and Definitions.

Penetration can be either "joint penetration" or "root penetration". The "joint penetration" is the size of the groove weld measured perpendicular to the surface of the base metal as in the case of a butt joint. How far into the base metal did the weld cause the metal melt and fuse? Root penetration is the distance into the root face, or beyond the bottom of the bevel, the weld melted or fused. 

Depth of fusion is measured perpendicular (or normal) to the bevel face (or fusion face after the weld is completed).

In the case of a fillet weld, the depth of fusion is the distance into the base metal melting occured. It is measured perpendicular to the flat surfaces on which the weld was deposited, i.e., the fusion faces of the joint.

I tried to include a sketch. I hope it helps.

Best regards - Al
Parent - - By CWI555 (*****) Date 03-18-2007 18:42

The question Shane had was in regards to ASME B31.3 Process piping. (ASME pressure piping B31.)
Some of the American standards contain different and or modified definitions as compared to there brethren.
Speaking in generalities There are two areas in American code for definitions unless otherwise specified in the specific code.

AWS 3.0 Standard Welding Terms and Definitions
ASME Section IX Qualification standard for welding and brazing procedures, welders, brazers, and welding and brazing operators
**Under ASME IX the relevant definitions are under QW 490 Definitions. Definitions beginning with QW/QB-492.
QB 491 states that there are terms listed specific to ASME code and are note defined by AWS 3.0, it further states that Several of the definitions have been modified slightly from A3.0 "so as to better define the context/intent as used in ASME Section IX. **
** area between asterisks important for definition later in post **
That difference between AWS and ASME has been the cause of much confusion for a lot of people in the past where the definitions vary from one to the other. Careful attention has to be paid to what code your welding or inspecting to for this reason. Even within the specific ASME code such as B31.3 specific variances can be found.

AWS defines the following:

depth of fusion. The distance that fusion extends into
the base metal or previous bead from the surface
melted during welding. See also joint

joint penetration. The distance the weld metal extends
from the weld face into a joint, exclusive of weld reinforcement.

By AWS definition you are correct for the most part.

ASME Section IX defines joint penetration the same as AWS.
However, for depth of fusion, there is no direct definition in ASME IX. IX breaks it down as follows:

Complete fusion - fusion which as occurred over the entire base material surfaces intended for welding, and between all layers and beads

fusion (fusion welding) - the melting together of filler metal and base metal, or of base metal only, to produce a weld.

Fusion face - a surface of the base metal that will be melted during welding

If you think your seeing a contradiction between this post and the response to Shanes original question you are, referred to **.

ASME intent is not always AWS intent and visa verse. Therefore the definitions vary depending on intent of the specific reference and code section.

My personal experience tells me to always pay attention to the code and standard definitions relevant to the current project for those reasons. 

I've been told there was a time when the standards varied sharply, but these days AWS and ASME are playing in the same sand box for the most part.

I've worked to EN standards, they vary slightly from the US version as well.

"CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom."

In this list is Germany and therefore the EN standards, would be what your used to. When I work to those standards I look up the specific definitions as a matter of course for the specific project for the same reasons as I do the ASME version.

Given all that, If your definitions came from the EN group then they are probably right. As I recall, AWS is pretty close in definitions to EN standards.

If anyone else has a different take on this please chime in.

Parent - - By aevald (*****) Date 03-18-2007 20:59 Edited 03-18-2007 21:39
Hello Stephan and Gerald and Al, as all of you have discussed these terms and their relative meanings, I believe the discrepancies come from more of a laymen's interpretation and misinterpretation of their meanings. Fusion, as I believe all of you stated, includes the boundary where the base metal has been affected by the welding that has occured and includes the weld metal that has been deposited or in the case of a fusion weld, the portion that has been melted by the process, this can also be verified by cutting, polishing, and etching in a cross section to better illustrate. Penetration COULD be perceived as the depth that a weld bead extends into a welded joint(similarly to the fusion statement), in the case of an open-root weld joint, SOME might term the weld reinforcement that extends past the surfaces of the inside or backside of this type of joint as penetration. Although I believe the correct term is actually root reinforcement. Hence, this is my thought, even though I might say that I have the proper amount of penetration(really root reinforcement) I might not have complete fusion. To further expand on my last sentence, if I didn't properly place the root pass on this open root joint I could have fused one side of the joint and not evenly fused both sides together and even though I might have the proper amount of root reinforcement this would not be an acceptable root weld due to incomplete fusion of the profile of the weld at all of it's points of contact to the base materials. Just my take on this, Regards, Allan
Parent - - By chuck meadows (***) Date 03-18-2007 23:49 Edited 03-18-2007 23:56
  I agree with you 100%, for what that's worth. A "cold" heat input can cause even excess penetration, but that does not necessarily mean that proper fusion was achieved. This is especially prominent in welding of high nickel alloys. Allan, your illustration was very precise and easy to understand, and in my opinion, 100% correct. Gerald and Al's comments were also very informative, but I don't think that penetration necessarily means that proper fusion was achieved. On the thousands of radiographs I've had the opportunity to grade, I've seen many open butt welds that graded as excess penetration, yet that "black line" on each of the walls of the base metal was present. To wit...excess penetration and lack of fusion. Both rejectable in most codes.  
Parent - - By DaveBoyer (*****) Date 03-19-2007 04:13
Chuck, This defect You mentioned in the last post- Am I corect in asuming that molten weld metal has "run into" the joint and cooled forming what looks like proper root reinforcement, but it is not fused due to lack of heat, meaning the parent metal never really melted in the bottom of the joint?
Parent - By chuck meadows (***) Date 03-19-2007 12:04
Dave, yes, that's what I was trying to say. That was not intended to say that there woule be a total lack of fusion all around thd joint configuration, though. Due to certain circumstances, the root bead can solidify before making proper fusion on the walls of the root pass.   
Parent - - By CWI555 (*****) Date 03-19-2007 07:38

My intent was not to say that all penetration is equal to proper fusion. Allan, Chuck, I happen to agree with you both on the matter as to what it actually is. However, based on the nature of Stephens question, I felt it necessary to point out that ASME and AWS codes have a different intended use of the definitions. I.E. The difference between lack of fusion and penetration. Lack of penetration as defined by the relevant ASME codes, in particular B31.3. On table 341.3.2 Girth, Miter Groove & Branch Connections a small measure of lack of penetration is allowed. It's not much, but it is still allowed. In the same table its zero tolerance for lack of fusion. Lack of penetration by default is lack of fusion as some part of the fusion face has not been fused, otherwise it would be a concave root Inversely as you've pointed out, penetration does not necessarily mean proper fusion either.

The intent of the code is clear. They mean to differentiate lack of fusion from lack of penetration even though it's one and the same. It's my interpretation that the allowable discontinuities are based on previously determined engineering and historical data analysis.

Which brings me back to the original intent of my post. The intent is what matters when grading a specific indication/discontinuity. Lack of pen? yep it's lack of fusion, but is it judged for being lack of fusion or lack of pen? therein is where the intent comes in and the differences in definitions given.

Parent - - By aevald (*****) Date 03-19-2007 13:11
Hello Gerald, I don't dissagree with what you said either, I guess I just had to throw it out there that some people might interpret this issue differently. When in reality they are one in the same or could be said to go hand in hand. I too appreciate the responses on all of the topics of the forum as they help me to realize different points of view and see the different perspectives relating to an issue. Thanks and regards, Allan
Parent - - By Stephan (***) Date 03-19-2007 14:55 Edited 03-19-2007 16:23
Dear Allan,
Dear Sirs,

although I had replied to the terrific information coming from you all - thanks for that - I have deleted this mentioned first response again (fortunately it was possible!). Reason was, that I thought to have understood when I had read what has came first from Al and Gerald. But afterwards I was - forgive me - a bit uncertain if I had really understood...

Therefore please correct me when I am wrong:

- There are different Standards or Codes, respectively,  being used in the United States of America i.e. ASME and AWS.

- Both dealing with the terminology "Penetration" and "Fusion" but having slight variations in regard to their interpretation.

- Whereas "lack of fusion" is strictly prohibited in all* (?) cases (relating to the excellent sketch coming from Al), "lack of penetration" is allowed under specific circumstances. This by all means is comparable to the German/European Standards.

- However, in some "real world" cases also a personal interpretation of "penetration" and "fusion" can take place, since actually both, "penetration" and "fusion", do mean the same, in an extended sense.

I hope that I have not complicated the topic too much.

Believe me or not!

I have received just a minute ago the February's AWS Welding Journal. It was the first time I haven't received it punctually since I am a AWS-member. Thanks to the great Rhenda Mayo from AWS, they have immediately sent another copy of the journal which I have received now, just a little too late, but nevertheless it is here! And what should I say...

By reading the Research Supplement (I love it) article "A Methodology for Prediction of Fusion Zone Shape" I could see what we are currently discussing about. It is... crazy!

Well and what could I recognize? Likewise there the terminology is a bit confusing (at least for me). Please see also:

Whereas within the articles "Introduction" the term "Fusion Zone" is being used by the authors, within the Figure 1, the term "Penetration" is used in coherence with "Fusion".

I hope I am right when I assume that this would cover the last stated point of "real-world" cases where the interpretation of "Fusion" and "Penetration" is lying in the personality of the viewer, isn't it?

Thanks and regards,

* In regard to Shane's topic. Is there a differentiation of "lack of fusion" between e.g. single "weaved" layers of a weld-cross-section and the "lack of fusion" on the e.g bevels of a weld-joint? Is the first allowed - since it might be interpreted as a "lack of penetration" - and the latter not - since it should be interpreted as a »pure« "lack of fusion"?
Parent - - By CWI555 (*****) Date 03-20-2007 19:12
again from section ASME section IX

Complete fusion - fusion which as occurred over the entire base material surfaces intended for welding, and between all layers and beads.

That definition defines complete fusion, anything that falls outside of that is lack of fusion. So in regards to the below quote:

* In regard to Shane's topic. Is there a differentiation of "lack of fusion" between e.g. single "weaved" layers of a weld-cross-section and the "lack of fusion" on the e.g bevels of a weld-joint? Is the first allowed - since it might be interpreted as a "lack of penetration" - and the latter not - since it should be interpreted as a »pure« "lack of fusion

In regards to interbead lack of fusion, B31.3 says zero tolorance. Assuming fusion face exclusive of the root area, zero lack of fusion allowed.
It's only in the root area that it gets a little grey.
Parent - By Stephan (***) Date 03-20-2007 22:09

Once more thank you, personally - and likewise all the others - hearty for taking your precious time and answer so precisely!

No more questions remained..!

My best wishes,
Parent - By andrew hamrick Date 03-20-2007 22:06
penetration is like welding a butt joint, flipping it over and have a good fill in on the back of the plate. And fusion is like welding a v groove and not pausing at the toe of the weld enough. Andy
Up Topic Welding Industry / Technical Discussions / "Penetration" or "Fusion"?

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