3.2,
It is a perfectly legitimate concern of Jons and I think it is strange myself.
The whole idea of a WPS is to ensure a sound weld, both mechanically and metallurgically. Can you honestly say the weld in the photograph supplied with no purge is a sound weld ? Based on ASME IX you can delete the purge on a s/s weld and it is considered acceptable.

Here is something that I find even more "interesting".
A PQR can be qualified on a 300 series s/s with purge.
A WPS could hypothetically be written based on that PQR for s/s without purge.
If a welder qualifies on P1 without purge he is qualified for various P numbers incuding P8.
The addition of purge is a non essential variable for welder quals so if he welds s/s then purge can be added.
However, based on ASME IX he can weld s/s without purge.
The deletion of purge is an essential variable for welder qualification but if he didn't use purge on the c/s qualification then he is not deleting it in production welding.
Any thoughts,
Cheers,
Shane

Well gents; even though I included my thoughts as fuel for further discussion, strangely enough after discussions with Mr. Sperko on the topic I have to say I agree with the ASME position, although I may still question it in my own mind.

Sugaring of the root may not be cause on it's own for failure of mechanical testing of the weld, it would likely be cause for failure due to a variety of inspection methods.  The WPS is intended to prove only the mechanical properties, if it doesn't fail, it doesn't fail.  On the other hand, the welder has the obligation of proving his ability to deposit "sound" weld metal and may be qualified through RT alone for many alloys (which is not allowed for the PQR).

Further, the use of P1 to qualify P1-P11, P4x etc., all have "similar" weldability even though some have peculiarities, that's where the shop or field engineer is supposed to handle these situations individually based on their application.  One example, was a recentl discussion I had with my Quality Department and they agreed to permit a welder qualified on P1 to weld P8 but they drew the line at P30 and P40 series saying they felt weldability was too different.  I had to agree, the puddle flow and manipulation require more attention to detail than those of the P1 - P11 series.

I am going to utilize section VIII for an example. similar logic can be found in the B pressure piping series, however; Section I utilizes a different take on it. For it, your interpretation is what I've used.

Visual criteria is fairly vague, however; if it is to be volumetrically tested it becomes clear. If it can be seen on the radiograph, it does in fact have an acceptance criteria.

Section VIII 07
uw 51
"(b) Indications shown on the radiographs of welds and
characterized as imperfections are unacceptable under the
following conditions and shall be repaired as provided in
UW-38, and the repair radiographed to UW-51"

"(1) any indication characterized as a crack or zone
of incomplete fusion or penetration;

(2) any other elongated indication on the radiograph
which has length greater than:"

"t = the thickness of the weld excluding any allowable
reinforcement. For a butt weld joining two members
having different thicknesses at the weld, t
is the thinner of these two thicknesses. If a full
penetration weld includes a fillet weld, the thickness
of the throat of the fillet shall be included in t."

If root oxidation is considered an 'imperfection' which I believe everyone is in agreement on, then it will fall to either criteria 1 or 2.
Without the ability to judge depth, criteria one is out. For a full penetration weld, it has to be filled to the full cross section with sound weld. However; while the image may be seen, there is no way to determine the depth of the affected area. Therefore lack of penetration cannot usually be used. If it creates a zone of lack of fusion, it's a no brainer.

Therein is the problem with the code being vague on the visual criteria. When it goes to volumetric, it is in effect addressed. So do you pass it off visually knowing it's going to reject on volumetric, or do you go ahead and repair it before burning up your NDE budget?

In my opinion, you've struck upon one of the largest vagaries in the ASME code. There are things that can be construed as being visually acceptable but reject on RT, and this is one of them.

Gerald,

most interesting discussion, to say the least.

Unfortunately I am having a lack of knowledge upon all the different steel grades P1... making it difficult to follow the arguments.

However, by having read what you and the others have posted, I mean to understand.

Honestly it surprises me that one of the most critical issues in welding 'stainless steels' even corrosion susceptibility after welding without purging is not addressed neither by AWS nor ASME.

That was the reason for me to ask again as e.g. in Germany nobody - at least in the industrial sector - would weld a stainless steel pipe without the appropriate precautions ensuring that the material may be used accordingly after welding.

I mean, there's a reason for using high alloyed or 'stainless' steels for particular applications, isn't it?

So when just having a look upon the 'mechanical' properties after welding without considering corrosion issues - with stainless steel welds - is a waste of time, money and nerves.

Hardly to understand...

Even that was also the reason for me to ask if that what's to be seen upon the photo is called 'sugaring'.

In Germany we are talking about a small but - from my point of view - important differentiation. Namely 'oxide layers' (Anlauffarben) - this what you've named '...yellow, gold, blue, grey, black...' and a kind of root 'combustion' (Verbrennung).

While the former might be acceptable as the oxide layer is not too thick (dark) and always depending upon the medium to be transmitted trough the pipe, the latter is rejectable by being irreparable and a mandatory reason for a 'cutout'.

So am I right by thinking - following Al - that for qualifying a particular stainless steel weld in the United States of America you have to meet both, either AWS or ASME codes for the 'mechanical' issues and NACE codes for 'corrosion' issues? Or am I missing something?

Hmmm... what's however almost harder for me to understand is, which silly a** has rated Jon's post a '1'?

Cheers and regards,
Stephan