Base metal discontinuities

Date 01-27-2010 05:22 Edited 01-27-2010 05:40

OK, here's the scenario. B31.1 Boiler External Piping.
RT came in and performed a marathon shooter session. All the welds passed with flying colors...COOL! (98% RT so far)
However, the P22 valves (pipe side and welds are good) have multiple indications. Now, the level ll RT tech did not record reject the Welds and marked accepted on the report...WTF???
So...
1) Do forged and cast parts fall under the same acceptance criteria as the weld? It is still visible in the film (of course) as cracks (longitudinal, transverse...you name it!) which is a big No-No.
2) RT tech is saying that the "indications" are outside the HAZ and makes them (in his defense) acceptable!
I'm no level lll, just lowly CWI clipboard packer.
3) How can the HAZ be determined on RT?

I say the RT report should have rejected the X-Rays so we can make the repairs (ie. MAKE THEM BUY NEW VALVES PLUS INSTALLATION TIME!!!) with back-charge.

As always...stuck between the bean counters (lower case intentional) and Interpretation!

help

BTW. btchn gig
475 MW mine mouth coal burner

By G.S.Crisi (****)

Date 01-27-2010 12:39

Answer to question 2:
Radiographic test detects discontinuities (porosity, lack of fusion, cracks, poor penetration etc. etc.) but does not determine the HAZ. In the HAZ the grains size is different (larger) than in the parent metal and X rays don't recognize the grain size. For that you must run a metallographic test, which used to be a destructive one. I've heard somewhere that there exist a portable metallographic mycroscope that allows you to make a test "in situ", but I'm not sure whether it's true.
Giovanni S. Crisi
Sao Paulo - Brazil

By Superflux (****)

Date 01-29-2010 04:52

Giovanni,

Thank you for the verification on limitations of RT sensitivity. The RT tech told me that their company policy was to limit base metal interpretations (B31.1) of discontinuities that are beyond 1/4" of the Heat Affected Zone. Apparently they have a corporate policy that predict and predetermines the HAZ. I could not understand how X-ray would be the correct method to determine HAZ!
Fortunately, I have been able to get Engineering and Upper management involved. They are very supportive and seem to enjoy solving even the most mundane problems.
My RFI will be answered tomorrow.

By CWI555

Date 01-28-2010 21:52

I am a level III and no the cast parts do not fall under the same acceptance criteria.

Be careful what you call a crack. They may in fact be shrinkage which would likely be acceptable.

If there were no rejectable indication in the "area of interest" then the RT tech did the right thing.
I would also caution against hacking into any of these valves prematurely, you would not be the first one to do so and risk their job when the things meet the standard they were ordered to.

The right way to proceed is to issue a concern and RFI as to the complete history, spec, etc of the valves. Then if you have concerns, call your RT company and get them to bring out the appropriate reference radiographs, and compare the indications you witnessed to the manufactures report.

Then and only then, "if" they are bad can you put the hammer down.

Regards,
Gerald

By Superflux (****)

Date 01-29-2010 01:57 Edited 01-29-2010 04:56

Gerald,

Thanx for the advice and Corrective Action suggestions. There was 1 shot that had a transverse linear indication extending from 1/4" in the weld to 3/4" into the base metal. This was rejected on the report. I have just pushed the issue up the chain of command and let the const. mgmt. firm deal with it.

On an off note...The RT tech has immaculate penmanship, what an unexpected pleasure. Seems like most NDE reports would task a 7th grade English teacher!

By rodofgod (**)

Date 01-27-2010 23:04 Edited 01-29-2010 06:22

Hi All!

Superflux,

I know where you are! Been there, got the 'T' Shirt!

Valves and associated castings usually fall under B16.34, and don't as a rule fall under the same acceptance criteria as a welded pipe joint. It addresses defects such as 'shrinkage cavities', 'sand inclusions, 'hot tears' and 'inserts' also cracks! From what I saw of the accompanying sample X-Rays, very lenient!
The RT tech is paid to shoot and interpret according to a standard, B31.1 in your case! If the weld area is good then its a pass, however, I would have expected him/her to note defects outside the welded area. This can then be shot up the ladder to the P.E. or Client, for them to decide if the defects in the v/v body are acceptable. On the job where this occurred that I was on, we had every pipe to v/v graph re-examined for possible casting defects.

HAZ can not be determined by RT by usual methods, It may be 'guessed at' by experienced operators! However there are several ways of accurately determining the HAZ by non destructive means. Replication and Field Metallurgical Inspection techniques are used in most power station main steam pipework systems to 'FIND' old welds that have been blended into the parent pipe for stress reasons and need to be reassessed!

Regards

By G.S.Crisi (****)

Date 01-28-2010 16:40

rodofgod,
would you explain briefly what those ways of determining the HAZ "in situ" (i.e., non destructively) consist of?
Thank you
Giovanni S. Crisi

By rodofgod (**)

Date 01-28-2010 22:20 Edited 01-28-2010 22:32

Hi Giovanni!
I'm no expert, but 'replication' is a way of examining the micro structure of the surface of the material by highly polishing and light etch, then application of an acetate film to the polished surface. This is then subjected to a solvent which will partially dissolve the film, but also imprints it with a mirror image of the previously etched material. The film is neutralised and mounted on a glass slide which can then be viewed under a microscope either on site or in a lab,they can even take high resolution pictures on site now!

This link provides a far better explanation:

http://www.tcreng.com/services/in-situ-metallography-replica-india.shtml

This is a picture I took some time ago, you can see the highly polished area near the top of the weld, where replication took place to find the old weld and the HAZ, so the machinist knew where to start the excavation and how much metal to take out to include the HAZ.

Hope this helps!

Regards

By Superflux (****)

Date 01-29-2010 05:43

rodofgod,

I love this forum for the comraderie of those who can "feel your pain".
It is way too easy to over-step the boundaries of one's job description and pay grade (being lowly QC boiler rat). My RT tech was 100% correct (by you) in his report and only rejected the one shot with a transverse indication that extended into the weld.
I am (much to my chagrin) not involved with Main Steam (boiler external piping only) on this project, but maybe this weekend (while ice fishing) will try to find the time to do some research into B16.34 (which is not in my limited library).

Copying from your response..."to 'FIND' old welds that have been blended into the parent pipe for stress reasons and need to be reassessed!"
My experience with inservice and antiquated steam systems has been mind blowing to see the erosion effects on the internal walls of pipe and vessels. To see metal gouged from turbulence like a garden hose sprayed on a playground sandbox, baffles common wisdom.

Once again, to all that have responded, thanks for the advice, and directions.

By rodofgod (**)

Date 01-31-2010 20:33

Hi All!

Superflux, it does indeed take some believing when you see heavy wall steam lines worn away like "a garden hose sprayed on a playground sandbox" - good description! To see a 2" boiler tube flapping around like a loose hosepipe, with the water turned on full, after a tube failure is also a sight!

Regards