Mr. Prasad,
API-1104 clause 5.6.3.3 accepts fish eye defects to a certain degree. In a pipe line welding qualification test, broken surfaces of nick break specimens or macro would show the fish eyes damages. Fish eye damage is typically influenced by:-
· Degree of cleanliness and inclusion level in the steel
· Degree of diffusible hydrogen content in the weld. This would be definitely high as cellulosic electrodes are used all through. Typically diffused hydrogen in the weld metal would accumulate around any materials defect, pores, metallic/non metallic inclusions, causing fish eye damages.
· Higher degree of fish eye may eventually cause hydrogen blistering over a period of time.
I would feel the ways to get around your problem would be one or a combination of these:-
1. Baking or re-drying of cellulosic electrodes are not recommended, because moisture is required for arc stability. Hence one good way to reduce moisture content would be to avoid prolonged exposure to environment and consume electrodes as fast as possible once the cans are opened.
2. As suggested by Mr. Prabhukumar, maintain the relatively higher degree of preheat and interpass temperature control , might be beneficial.
3. If the above is not feasible, perform post weld hydrogen bake out 2000C, for 1hr/inch of thickness, this would help to diffuse the hydrogen out. You may try this on test coupon, with and without bake out and see the results.
4. As suggested by Mr. Prabhukumar, instead of performing complete welding by cellulosic electrode, switch to a combination of E7010-P1 (Cellulose root pass+1 ) rest E8045-P2 (Basic-Low H2, vertical down welding ).Contact the electrode manufacturer, and discus this issue, if fish eyes are totally out of control.
Some degrees of fish eye defects are acceptable by pipeline codes, but the excess of it would harm the steel.
I have attached some catalogues which explains why it happens, metallurgical features, and how to tackle the problem (the article from Bohler).
Thanks.
Pradip Goswami, P.Eng.
Welding & Metallurgical Engineer/Specialist
Ontario Power Generation Inc.
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net
Date: Thu, 17 Jun 2010 11:52:13 +0300
Subject: Re: [MW:5632] RE: 5625] fish eyes in welding
From: weldengr.velosi@gmail.com
To: materials-welding@googlegroups.com
Dear Mr. Prabhukumar,
Thank you very much for your reply.
As it is pipe line it is very difficult to carryout prehating and post heating for all weld joints and the same pipes and consumables were used by our competitors and they do not have any problem with fish eyes and infect they have done without preheat.
I have double about the hydrogen content in electrode. There is no limit on hydrogen content for cellulose electrodes. Is it possible some batch of electrodes contain more hydrogen content and some batch contain less hydrogen content.
We have not observed any fisheyes in marco and nick break specimen. The impact energy also has come more than 100 J at -10 C.
Regards
N.V. PRASAD
On Thu, Jun 17, 2010 at 8:10 AM, Prabhu Kumar L <l.prabhukumar@saipem-india.com> wrote:
Dear Mr. Prasad,
In case of fish eye defect due to hydrogen embitterment, this can also be visualized in nick break samples. Please check the nick break samples for confirmation. If it is not possible by 5 or 10X magnification, you can also verify with higher magnification which will identify the defect. This defect may be developed after 24 hours or later in the completed welds. The following precaution may help to prevent the fish eye defect.
- Use increased preheat of 100 Deg. C and interpass temperature of around 200-250 Deg. C in order to diffuse out the hydrogen present in the weld metal. The rate of hydrogen diffusion will increase if temperature increases.
- Use E6010 type electrode for root welding instead of E7010P1 type, in order to have better ductility to observe high thermal stresses during welding and subsequent passes can be used with matching electrodes such as E8010P1. E6010 is the best electrode for root application for pipe materials upto X80. See the attached catalogue from Bohler-Thyssen welding.
Alternatively you can try with low hydrogen downhill welding for high yield pipeline materials such as X65 and above. Recommend electrode is E8045-P2 (Brand name Bohler FOX BVD 85). Refer attached catalogue.
Regards,
L. Prabhu kumar,
Sr. Principal Engineer,
Equipments & Materials Dept.,
Saipem India Projects Limited,
Nungambakkam High Road, Chennai - 600 034, India.
Tel:+91 44 43906588, Ext.: 588, Fax:+91 44 66840345,
Mobile Ph. No.: +91 9003010978.
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of N VENKATESWARA PRASAD
Sent: Wednesday, June 16, 2010 11:27 PM
To: materials-welding@googlegroups.com
Subject: [MW:5625] fish eyes in welding
Dear All,
I have carried out Welding procedure qualification for pipe line as per the details given below
Code of fabrication : API 1104
BASE MATERIAL: 36" DIA API 5L X 65 PIPE to PIPE ( Thickness 16 mm)
FILLER WIRE : E 7010 P1 for Root pass and E 8010 P1 for hot and fill passes ( lincoln electordes pipe liner 7P+ and 8 P+)
Preheating : 65 C
Interpass temp : 95 C max.
We have conducted Transverse tensile test, longitudinal tensile test ( All weld tensile test), side bend test, nick break test, macro and harndess tests.
The specimens have passed all the above tests except longitudinal tensile test i.e all weld tensile test. In this test we got very good UTS and YS ie around 660 and 580 MPa respectively but elongation has come only 16.5 % against requirement of 19%. First we have done two tests and got 14.5 & 16.5 % elongation respectively,. But later we have 4 more specimens, in that 3 has shown 19% and one has shown 13% Elongation only. ( The elongation of base metal and electrodes is around 24%)
The reason for low elongation is fish eyes in welding.
WE have taken all precautions i.e. maintaining proper preheat throughout the welding and proper cleaning before welding. The fisheyes occurs due to hydrogen embrittlement. As the electrodes are cellulose electrodes so hydrogen content will be there in welding. This type of fisheyes are not observed in any other contractors did welding of same pipes.
Now any how the elongation is just in the border and less elongation only due to fish eyes, so client has accepted this results asked to go-ahead for CTOD test.
The CTOD test has to be done at -10 C, i have apprehension that this fisheyes may not give required results in CTOD.
May please give your views on fish eyes in welding and how to avoid the same during welding.
Regards
N.V. PRASAD
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THIS MESSAGE IS ONLY INTENDED FOR THE USE OF THE INTENDED RECIPIENT(S) AND MAY CONTAIN INFORMATION THAT IS PRIVILEGED, PROPRIETARY AND/OR CONFIDENTIAL. If you are not the intended recipient, you are hereby notified that any review, retransmission, dissemination, distribution, copying, conversion to hard copy or other use of this communication is strictly prohibited. If you are not the intended recipient and have received this message in error, please notify me by return e-mail and delete this message from your system. Ontario Power Generation Inc.
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