Unknown Indication

Date 06-21-2011 00:32 Edited 06-21-2011 00:34

16% of copper in SA 516 Gr 70 is unthinkable. Where did that copper come from? Deep mistery for Sherlock Holmes to investigate.
An idea: was the grinding wheel used to grind copper before it was used on your pressure vessel?
What I can say is that after a removal of 3,2 mm (1/8 inch) from the parent metal, chances are that you have gone beyond the corrosion allowance (i.e., the one that has been left to cater for corrosion) and penetrated the sound metal (i.e., the one that was calculated to wuthstand pressure).
I recommend you to check if this happened. If so, I'd say that the vessel is condamned, unless you boys put your heads together and search for an acceptable solution.
Giovanni S. Crisi
Sao Paulo - Brazil

By jon20013 (*****)

Date 06-21-2011 03:04 Edited 06-21-2011 04:36

Shane... good one! :0-

I would not expect copper to penetrate the base metal as deeply as you mention without some very obvious indications. Have you tried acid etching the areas?

I also have some doubts as to whether your steel would be hardenable from your observations but defer to others who are wiser in that field than myself.

Now, putting on my QA/QC hat.... you've likely voided any manufacturers warranty by excavating (along with any stamp the vessel may have had). Probably better to put an immediate hold on any further destructive works and contact your procurement group. I'm assuming the supplier has been contacted??

EDIT: Now just thinking stupid thoughts, you mention the area appears to have been previously ground; could be inadequate preheating might have lead to the spider web effect if its in an area where a temporary attachment might have been placed... Now the stupid part: wonder if it were a temporary attachment what the filler might have been.... maybe Cuni in error?

By DaveBoyer (*****)

Date 06-21-2011 03:12

Perhaps an inclusion in the material the vessel was made from?

I have heard of loose parts & junk getting rolled into plate steel, but havn't seen it first hand.

By 803056

Date 06-21-2011 03:25

Without a photograph or any other helpful clues, any suggestion offered is pure conjecture.

My vote would be a welded repair of a mislocated hole where copper was used as backing.

That's my guess of what the mystery indication is and while we're at it, my guess on the number of jelly beans in the jar is 2 222! :cool:

Best regards - Al

By jarcher (**)

Date 06-21-2011 03:29

I hate to disagree with either Jon or the Prof here, but it looks as if evidence to a cable arcing out during manufacture. I would think the casual arc strike would not penetrate 1/8". But the high copper content along with the high hardness of the area (516-70 might well be in that range as welded) makes the most likely cause to be the arc out of a welding cable that was draped across the shell. This might well have caused pit 1/8 or more deep. The pit might then have been excavated (insufficiently it would seem) and rewelded. Just a guess, but it seems the most likely scenario given the physical conditions you report.

By Shane Feder (****)

Date 06-21-2011 03:53

How do I post a picture guys ?

Attachment: Defect1.doc (421k)

By js55

Date 06-21-2011 11:57

The usual sources of copper are being offered but it seems unlikely that you would place your PMI gun at the exact point of the arc (backing bar more likely) contact and contamination. And even with that it shouldn't read 25%. However, PMI machines are not full proof. I get misreadings from them all the time (not that extreme usually). Depending upon your time frame, and if you have the budget and inclination I would take shavings and send them to a lab for wet chems. Also, take multiple readings in concentric circles out from the crack and pattern the chemistry. If its contamination from some hard source there should be some kind of pattern emerge. The other thing is, if it is contamination from a hard source it seems unlikely that after grinding the contamination would still register.

By 803056

Date 06-21-2011 19:12

Use a soft disk to clean up the area where the cracks are observed and etch the area to identify any heat affected zone that might be present if there was a welded repair. Even if the vessel was stress relieved after the welded repair was made, the temperature wouldn't be high enough to remove evidence of a HAZ. Copper inclusions will be evident when the area is etched.

I do not discount the possibility of a welding lead or possibly the lead used for magnetic prod testing being dragged across the vessel. The difference is that the welding lead could be "hot" all the time if the fabricator was using SMAW. The lead for MT would carry higher current and would be "hot" only when the system was energized while magnetizing the prods. I had a similar incident on a cast iron paper roll. The paper company argued the copper inclusion on the face of the roll was a casting defect. I argued I could replicate the inclusion (and I did) by placing a copper bolt into the electrode holder and dragging it across the face of the dmaged paper roll. When all was said and done, the paper company admitted that the power cable to an electric heater was disconnected and swang down and struck the face of the paper roll. My demonstration of how to make a copper inclusion saved my client nearly 100K. They sold the paper company a new roll rather than giving the paper company a new replacement roll for free.

I have seen similar cracks where the fabricator attempted to repair a mislocated hole and used a copper backing bar. The only difference was that the outline of the original weld and the cracks were confined to the diameter of the mislocated hole.

Best regards - Al

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

Date 06-21-2011 19:02

Another idea.
The vessel has been heat treated by induction after welding. When using induction heating, insulated copper cables are wrapped onto the vessel (or piping, according to the case) to make a coil of which the vessel becomes the nucleous.
It's possible that the cable was old and used and had a 1 inch diameter hole in the insulation. Not noticing the hole, the PWSHT crew installed the cable and let high frequency current to pass within it. The naked portion of the cable touched the vessel wall and flashes were produced, causing the melting of some copper and steel. Then, the molten metal solidified as a copper - iron alloy.
Of course, it's just a guess.
Giovanni S. Crisi

PS. Induction PWHT is an old method that has been replaced by resistance heating, but there are still people who use it.

By nantong (**)

Date 06-21-2011 22:01

Overseas vessel Shane? Where was the steel made? Might be copper from a recycled washing machine if it is inside the material and not on the surface.

How's Pluto?

By Shane Feder (****)

Date 06-21-2011 23:18

Guys,
Thank you all for your responses.
Not sure of the original cause but starting to think that maybe the copper readings are coming from welding over some embedded copper (arc out) or copper that has been "smeared" into the parent metal by the grinder.
We had similar on a previous project where titanium was "smeared" into the parent metal by the grinder resulting in cracks once it was welded over.

Nantong,
The vessels were made by the same company that supplied the defective S/S tanks in New Caledonia.
Looks like we have got similar to the Fleater Vessels issue over again with major cracking being discovered in some vessels after receipt on site - nearly all of them look like they were caused by lack of or insufficient preheat.
When will companies learn that the perceived high cost of an inspector at the fabrication stage is miniscule compared to possible repair costs onsite - especially when re-PWHT and re-Hydrotesting are required,
Cheers,
Shane

By jon20013 (*****)

Date 06-22-2011 02:42

From my back to back, a French colleague who, although young is a very good mechanical engineer and degreed metallurgist:

"This is a typical fabrication mistake from the steel maker.

This arrive when a Copper or bronze bolt or anything else similar fall on the "Brame" or ingot before lamination or heating and lamination.

Such defect don't appear during the fabrication, but right after the cold forming of the plate for the fabrication.

In this case you friends, should get support of a metallurgist who is familiar with steel manufacturing processes and mistake and complain to the steel maker. This is very easy to demonstrate.

Please tell me if they need additional information on this."

By DaveBoyer (*****)

Date 06-22-2011 02:59

This is what I was describing, altho My gut feeling is that a poorly done repair from cable arcing, mislocated drilling, or some other defect/screwup is probably more likely to have happened.

Since the original post Shane has mentioned that the source of this part has shipped poor quality parts before. This being the case, they are not quality concious period, so manufacturing mistakes or material defects might be expected.

By Shane Feder (****)

Date 06-22-2011 05:00

Thanks guys,
Can anyone assist with my next problem.
Is there any chemical we can apply to the suspect area to confirm all the copper has been removed ?
If the copper has been smeared by a grinder as soon as we reweld the excavated area there is a strong possibility we will have recracking,
Regards,
Shane

By Superflux (****)

Date 06-22-2011 08:03

Sulfuric acid will turn copper green

By jon20013 (*****)

Date 06-22-2011 08:57

Shane, good old fashioned acid etch. Formula in back section of ASME IX but basically nitric acid and water. Of course make sure you put acid into water and not vice versa and use a glass or plastic container, lol!

By nantong (**)

Date 06-22-2011 12:44

Shane, I was not joking about "a washing machine". In steel making a quantity of scrap steel is used. I know from my experience with British Steel. If the steel manufacturer does not seperate the ferrous and non-ferrous material adequately then you run the risk of "a washing machine" with the copper windings of the electric motor in the steel. This is a well known problem. If you are finding this problem in foreign pressure vessel plate then there is only one course of action, scrap and remake with material from a reputable company. I do not know how it stands in Australia but certainly in Europe you will be found negligent if a vessel fails in service and you just repair the isolated areas you have found but have not determined the possible extent of the problem.

Due diligence Shane.

By Shane Feder (****)

Date 06-23-2011 01:46

You forget Nantong,
I am just the eyes and the ears for the Welding Engineer.
If a vessel fails in service due to negligence then it is the guy who earns a gold bar a week who will be sitting in court - not the guy on a bag of rice a week. LOL !
Cheers,
Shane

By 99205

Date 06-23-2011 02:12

So true but if they can prove the Ears didn't tell all they heard or the Eyes didn't tell all they saw then the sword of justice will point in your direction.

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

Date 06-22-2011 13:32

Gentlemen,
Let a chemical engineer speak. What Shane wants is to check in a second whether the copper has been completely removed.
Copper sulfate is blue, but if you drop sulfuric acid into the hole it'll be somewhat difficult to observe the blue color, even if the chemical reaction between the acid and copper has taken place.
Moreover, by adding acid, either sulfuric or nitric, you'll attack and dissolve also the sound metal, which you don't want.
What Shane has to do is to put a few drops of liquid ammonia into the hole, and if there's copper the chemical reaction is instantaneous: ammonia reacts with copper to produce cupric diamine which is deep blue in color and leaves the steel unattacked.

Now I'd like to say another thing. One of us, frequentors of this Forum (I don't remember who), has the following motto written under his postings: You don't get what you pay for, you get what you inspected. A good lesson to learn.

Giovanni S. Crisi

By Shane Feder (****)

Date 07-28-2011 05:31 Edited 07-28-2011 05:41

Hello Giovanni,
I just went back to this post to print your response out and discovered I never thanked you for your informative response.
Much appreciated.
We have to check one other plate from the same batch to ensure there are no inclusions in it.
1 What strength (percentage) ammonia do we require ?
2 If it is diluted we may be able to spray over the whole plate - will it still work if diluted ?
3 Are the fumes from cupric diamine hazardous ?

Regards,
Shane

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

Date 07-28-2011 14:50

Shane,
It's a pleasure to be of service to you.

Ammonia (chemical formula NH3) is a gas, so it's commonly used as an aqueous solution, usually called "liquid ammonia". It's not difficult to find liquid ammonia, any chemical lab has a bottle of it. Here in Brazil (I don't know in other countries) you can buy it at pharmacies, or drugstores, as Americans say.
Liquid ammonia is prepared as a saturated solution of gaseous ammonia in water. But ammonia is highly volatile, so the saturated solution doesn't last very long. This is why the actual solution concentration isn't warranted by the vendors. You can have your bottle very well sealed with a rubber plug (ammonia doesn't corrode rubber) but when you open it some gaseous ammonia will come off leaving a strong and penetrant odor, which chemists know very well. Ammonia isn't harmful to the skin but it is to the lungs, so when it's used in industries a breathing mask should be used. In chemical laboratories it's not necessary to use the mask: chemists are quite used in handling ammonia.

Having said that, the answers to your questions are:
1. Use the liquid ammonia contained in the bottle that you people bought from a supplier. As I said, it was first prepared as a saturated solution but after a couple of weeks it's not saturated any more.
2. Spraying will sparge the ammonia odor all over your plant and someone will complain. Just wet the plate surface with liquid ammonia.
3. Ammonia fumes are hazardous. People handling it should wear breathing mask. It doesn't attack skin, but use gloves anyway.

Giovanni S. Crisi