[MW:5625] fish eyes in welding

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

 

 

 

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