notch toughness failure

[saipemsmspetti]

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

 

[saipemsmspetti]

Thanks gramph1

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.

 

[saipemsmspetti]

Thanks stanweld.
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 .

 

[stanweld]

saipemsmspetti,
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.

 

[unclesyd]

saipemsmspetti,

It looks like your welding problem is the least of your worries.

http://www.iht.com/articles/2006/09/19/business/sakhalin.php

 

[saipemsmspetti]

I am afraid I did not understand you unclesyd. Why you said so?
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.

 

[unclesyd]

It was on the news here that the Russian Government had revoked your environmental permit.

 

[unclesyd]

salpemsmspetti,

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

 

[saipemsmspetti]

unclesyd

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.

 

[unclesyd]

Great news on both subjects.

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.