fish eyes in welding

[N VENKATESWARA PRASAD]

Dear All,

 

I have carried out Welding procedure qualificaiton 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 repsectively,.  But later we have 4 more speciments, 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 through out the welding and proper cleaning before welding.  The fisheyes occues 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 contracters did welding of same pipes.

 

Now any how the elongation is just in the border and less elongation only due to fish eyes, so cleint has accepted this results asked to goahead 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

 

 

 

[Prabhu Kumar L]

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.

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[N VENKATESWARA PRASAD]

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 competetors and they donot have any problem with fish eyes and infact they have done with out 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

[AGUSTIN JIMENEZ]

Hi PRASAD.

I know fish eye problem how burn through 9.3.7 in API 1104 - 2007, the welder too affect the weld, not only electrode, I worked with API 5L X65, I recomended that you do rediographic inspection and later destructive test, so your checks for the presence of discontinuities that may affect the test.

I hope tha information was utility for you.

 

Agustin

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De: N VENKATESWARA PRASAD <weldeng...@gmail.com>
Para: material...@googlegroups.com
Enviado: jue, junio 17, 2010 4:22:13 AM
Asunto: Re: [MW:5632] RE: 5625] fish eyes in welding