notch toughness failure
notch toughness failure
(OP)
In this moment I am working as welding engineer on Sakhalin pipeline project. In the last few weeks we are faced with constant notch toughness failures in welding qualification program. In spite of all my experience there is lack of time and possibility to explore the problem in details and pressure to continue with on site works.
The short description of the problem:
Base material: API 5L X65 pipe 48"x34.4 mm
(CE=0.34%, PCM=0.15%)
GTAW (root)+ SMAW (5G position, uphill)
ER70S-6 + E8018-G
Heat input:Q=15-18 KJ/cm (for root and 1&2 fill)
Q=22-38 KJ/cm (to complete)
Preheat: 125 deg. C (Used induction heaters to preheat whole coupon and to keep preheating temperature all the time)
Interpass: 250 deg. C
PWHT: At 580 +/- 20 deg C for 1.5 hour soaking
We have constantly repeated CVN failures but only in the root weld metal and in the root fusion line (10x10 CVN specimen taken 2 mm in depth from the root surface).
Testing temperature: -35 deg C (CVN permitted av.=45 J, min=34 J)
In the same time hardness values are good across the whole welding joint (260 HV) as a result of PWHT.
To investigate a problem we ordered microstructure photos of this part of the weld joint (as minimum waste of time) to make some decisions.
Waiting the respond of this test, I am afraid of what should I be able to decide and what to expect.
Can I expect a grain coarsening as the main reason, or some precipitates on the grain boundaries or perhaps some martensitic or bainitic structure?
Is the problem with to much time on a peak temperature of welding cycle or too small cooling rate between 800 and 500 deg C?
Is PWHT that one to deteriorate toughness, but only in the root region.
What should be the right step to improve toughness and solve this problem
Thank you very much in advance
The short description of the problem:
Base material: API 5L X65 pipe 48"x34.4 mm
(CE=0.34%, PCM=0.15%)
GTAW (root)+ SMAW (5G position, uphill)
ER70S-6 + E8018-G
Heat input:Q=15-18 KJ/cm (for root and 1&2 fill)
Q=22-38 KJ/cm (to complete)
Preheat: 125 deg. C (Used induction heaters to preheat whole coupon and to keep preheating temperature all the time)
Interpass: 250 deg. C
PWHT: At 580 +/- 20 deg C for 1.5 hour soaking
We have constantly repeated CVN failures but only in the root weld metal and in the root fusion line (10x10 CVN specimen taken 2 mm in depth from the root surface).
Testing temperature: -35 deg C (CVN permitted av.=45 J, min=34 J)
In the same time hardness values are good across the whole welding joint (260 HV) as a result of PWHT.
To investigate a problem we ordered microstructure photos of this part of the weld joint (as minimum waste of time) to make some decisions.
Waiting the respond of this test, I am afraid of what should I be able to decide and what to expect.
Can I expect a grain coarsening as the main reason, or some precipitates on the grain boundaries or perhaps some martensitic or bainitic structure?
Is the problem with to much time on a peak temperature of welding cycle or too small cooling rate between 800 and 500 deg C?
Is PWHT that one to deteriorate toughness, but only in the root region.
What should be the right step to improve toughness and solve this problem
Thank you very much in advance





RE: notch toughness failure
What is the actual chemical composition of the SFA 5.5 E8018-G weld rod? Why are you even using this weld rod, when no impacts are specified?
Also are you aware that for ER70S-6 electrode and wire supplied in accordance with SFA 5.18, minimum impact requirements as-welded is 27J at -30 deg C.
RE: notch toughness failure
E8018-G is BOHLER electrode FOX EV 65 with:
C=0.06
Si=0.3
Mn=1.2
Ni=0.8
Mo=0.35
with 80J at -60 deg. C from BOHLER catalog
ER70S-6 is ESAB rod OK Tigrod 12.64 with:
C=0.1
Si=1.0
Mn=1.7
with 47J at -40 deg. C or
with 70J at -30 deg. C per ESAB catalog
If I am concerned about consumable choice it is maybe OK Tigrod 12.64. I thought OK Tigrod 13.13 would be better choice. This is one of my ideas to try to solve this problem. But I think FOX EV 65 is good choice because the results of the rest of weld section were with very good notch toughness.
RE: notch toughness failure
The scene was of a TIG welder making what looked like a third pass, root + hot + 1 additional, using the "walking the cup technique". This in itself usually falls under it's OK but I have seen some problems on welding using this technique where the welder dwells too long. This is especially true on wide welds.
It has been our policy to limit the "walking the cup" technique to the root and hot pass only on alloy steel piping.
RE: notch toughness failure
I do not know about this application of TIG as a third pass. What should be the purpose of it? Usualy TIG is used for the root and after from the hot to the cup passes SMAW is used.
But you gave me an idea with "walking the cup technique".
I suspect in grain coarsening present in the root weld metal and HAZ. Maybe is this technique with dwelling too long by sides of root pass that caused grain growth. I will see the microphotos of this region that I am expecting to get soon to check it. Your last sentence said that for X65 we should have be very careful with using TIG with such technique.
RE: notch toughness failure
RE: notch toughness failure
RE: notch toughness failure
I would also agree with Stanweld to check your dilution. The root pass composition could be quite different than the manufacturer's analysis. Make sure plenty of filler wire is added to the root pass to help with this potential issue.
RE: notch toughness failure
A good welder will want to use a "feather edge" weld prep, no gap, for the root. We haven't seen any problems with this approach and use it for all piping in polymer service. In fact this technique is used in 90% of piping on site, again only the root + hot with SMAW fill and cap.
Welders that are proficient with the process will want to completely weldout the joint if possible. The don't like to "stick" weld.
Some welders can and will carry a tremendous amount of weld metal with this process. They will double by twisting the stated wire size.
I agree the a quick macro etch might tell a lot about the microstructure. I would also get some micro samples.
RE: notch toughness failure
We have 3.5-4.2mm root gap which means less dilution in the root then with no gap. Do you prefer as much as possible less dilution and smaller amount of weld metal in the root.
Please can you explain me in more details your sentences and terms in quotations because it is some sort of sleng and my english is not native.
-"feather edge"
-"walking the cup"
-weldout the joint
-"stick" weld.
-double by twisting the stated wire size.
RE: notch toughness failure
I think I will follow your instruction to use ER80S-D2 or any other with properties after PWHT.
Your words 'Make sure plenty of filler wire is added to the root pass to help with this potential issue' mean that it is necessary to have such technique to diminish dilution with as much as possible shear of filler metal in the root pass and less melting of BM.
This is somahow in contradiction with 'unclesyd's opinion.
Why do you mention lower PWHT temperature and lower noch toughness results.Should I have to make PWHT on higher temp. than 580 deg. C to get some better results.
RE: notch toughness failure
It is true. We did had 4.65 - 6.22 cm/min speed for GTAW.
Regarding chem. content of X65 find it below and tell me your opinion:
C=0.077/Si=0.282/Mn=1.61/Mo=0.014/Ni=0.272/Cr=0.041/V=0.075/Cu=0.218/Nb=0.045/Ti=0.002/P=0.014/S=0.00008/N=0.0038 and small amounts of As,Sb,Ca,Bi
Speaking of dilution can you explain which process is taking place in your opinion during root pass, regarding diffusion and changing the chenical content of this region.
Who is the main to blame for dilution.
RE: notch toughness failure
You have been given some excellent suggestions that may or may not solve your problem. I would wait until you receive the results back from the lab to confirm one or more of the suggestions mentioned above.
RE: notch toughness failure
Anyway I will try to use other rod for GTAW (with PWHT garanteed values)and take a care about welders skill and technique.
Please, contribute once more with your opinion, after receiving all asked clearances from the others.
It is very good sentence of yours 'may or may not'.Just like Pitia the Greek prophet woman. (Ibis, redibis nunquam in bello peribis)
RE: notch toughness failure
"May or may not" is a very popular phrase around my house especially with my two daughters that attend college.
RE: notch toughness failure
Higher PWHT temperature in low alloy steel (at least up to 1100F minimum) in my experience seems to help CVN values. PWHT below 1100F can be challenging. As an example, with E12018M2, we get poor CVN values with 1075F PWHT, and great values with 1175F PWHT. Other alloys may not be as extreme, but seem to follow the same trend when we test CVN properties. The exception may be carbon steel FCAW, which starts to degrade above 1150F or more. I would temper as high as the base metal allows (i.e. 25F-50F below base metal tempering temperature). If pipe is as-rolled, you may need to conduct some experiments to see how it responds to different temperatures.
RE: notch toughness failure
"Feather edge" This is weld prep where the their is no land on the weld prep, it is one single angle. The edges are touching and there is no gap. The welder likes the surface of the weld prep to be very smooth.
"Weldout the joint" This is a term used to convey the process of completing or finishing the weld joint after the root and hot pass are completed.
"Stick weld" This welding with a covered electrode, SMAW.
"Double by twisting" This is process where one takes two of the same size wires and twist them together to effectively make a large electrode to carry more metal. A lot welders have a little jig that will make a very tight twist of say two 1/16" wires to make a 1/8" equivalent.
Though my experience with low alloy pipe is some what limited we tended to minimize the dilution in root pass of these alloys. Fortunately we never had any requirements for low temperature high impact values other than Ammonia Piping.
I forgot to mention that you have one heck of a project underway. I know why you you need the low temperature impact values as I was stationed across the Sakhalin straight on Northern Hokkaido for several months during the middle of winter while in the military.
RE: notch toughness failure
RE: notch toughness failure
Look for LBZ's Local Brittle Zones along the Fusion Line which would show up as harder areas vs the majority of the HAZ. You have low Pcm but are still getting 260HV with very reasonable arc energy. I would have guessed hardness below 250. The high Nb+V could be responsible through secondary hardening.
Are you sure that preheat is being applied and that interpass is maintained above the required preheat until completion?
Were weld metal consumables batch tested for impacts in the PWHT condition you specified, before purchase? Were consumable brand and designation required supplementary essential variables?
Sometimes it takes a stronger root consumable to match the higher impacts for the higher strength base metal. The typical undermatch in the root I think concentrates strain in the weld metal and makes it less tough than base metal.
RE: notch toughness failure
I have used ER80S-Ni1 to weld the root in similar pipe subject to PWHT to provide required absorbed energy.
RE: notch toughness failure
Sorry for neglecting forum for a last week, but today I found some interesting contributions.
First, hardness values in WM and HAZ after PWHT were much lower than 250 HV with only two peaks in pipe side (with chemical content stated in one of my previous messages). May be it has some conection with Nb and V carbides.
The content of Nb,V and Al in this pipe were:
Al=0.0031; V=0.075; Nb=0.045
Is it considerably higher in your experiance?
Regarding preheating and interpass everyting was controled but consumables none was with tested CVN values after PWHT.
We are now on the way to change ER 80S-Ni1 for the root.
RE: notch toughness failure
I have the same question for you as I asked grampi1.
The content of Nb,V and Al in the pipe were:
Al=0.0031; V=0.075; Nb=0.045
Is it considerably higher in your experiance to contribute to diminish CVN particularly after PWHT?
We are now on the way to change ER 80S-Ni1 (Elgatig 162) for the root.I hope it will solve the problem .
RE: notch toughness failure
Fine grain melting for your pipe did not use Aluminum. By 1976 we mandated controls on V & Nb (V + NB < .10) and stipulated fine grain melting through Al additions. I guess we get to reinvent the wheel every generation. Whereas I have not specified steel making requirments for low temp X65/X70 pipe since 1993, I am not fully aware of today's practices. Through my experience, your pipe's chemistry would provide excellent properties in the as-welded condition.
RE: notch toughness failure
It looks like your welding problem is the least of your worries.
http://www
RE: notch toughness failure
Anyway, today we shall have the sample welded after all useful suggestions applied. In a few days will be the test reports and I shall let you know here about them.
RE: notch toughness failure
RE: notch toughness failure
If you are still checking Eng-Tips please let us know how you and your project fared in the big quake yesterday (10/15/06).
unclesyd
RE: notch toughness failure
I am still checking this page but not from Sakhalin.I left Sakhalin project a month ago because of some other tasks in Europe. I was learned by my colleagues that nothing special has been happened on the project after earthquake. They even didn't feel it.
Concerning the problem we were discussing through this thread I can inform you with pleasure that we succeeded to get good results of notch toughness in repeated qualification. The main changes to succeed was to change GTAW or SMAW consumable for root with 1% Ni, with technique (speed above 6.5 cm/min) and only 3.2 mm dia. electrode for filling passes (forget dia 4 if you have to test CVN at -45 deg. C). Once again thanks to everybody that participate in discussion.
RE: notch toughness failure
Thanks for the update on your original post that the problem has been resolved. I'm sure that other members will file this bit information for the resolution of any future problems concerning notch toughness.
Looking forward to your participation in future discussions.