Gas pockets

Date 01-28-2008 23:18

I have been on a pipeline under 1104 and one day they had me stick around after tieing in untill inspections were done. Because I had nothing else going on I went in the dark room to look at the X-rays. The technition was showing me my welds when I saw a little spec in one of them. I asked him if it was slag or what it was. He just said it was a little gas pocket. I guess it was nothing really because he didn't seem to worry about and it passed the code no problem. I was just wondering what causes that little gas pocket and how I can prevent that from happening again? THANKS

By dbigkahunna (****)

Date 01-29-2008 00:19

SMAW will tend to have GP. That is why ther is a code allowable for size and number. Some rods like the old Fleetweld 85 and 85P just had porosity. You could grind until you wore out a 9 incher and there still would be porosity. THat is why there are few perfect welds. What you want is acceptable welds. Capping with 5P+ sometimes you get a gp in the weld and you dont see it until you brush it. If all you had was one GP on a tie in, good job!
BABRT's

By CK Welding (**)

Date 01-29-2008 02:07

Well thank you. I guess nobody ever taught me anything about that sort of stuff. I was just taught how to weld and make them perfect. As far as I knew they were all perfect because I never looked at the pictures before and I passed under every code I ever welded under. Codes never really mean anything to me, I just make every weld to the best of my abuilty and let the inspector take care of the rest. Where can I get an discription of what is and isn't exceptable for each code.

By CWI555

Date 01-29-2008 02:31 Edited 01-29-2008 02:34

The relevant codes each have their acceptance criteria. You can either buy them (which is expensive) or get one of those inspectors to give you a copy of the acceptance criteria for whatever code your concerned with. As for the porosity, It's gas pores are more the rule than the exception for your case. As Dbigkaunna stated, if your just showing a tiny pore, good job.

By CK Welding (**)

Date 01-29-2008 03:08

What causes gas pores? Long arc, To close, just happens knowbody knows? Just courious.

By nosetackle (**)

Date 01-29-2008 04:57

http://www.meg.co.uk/courses/gl.php

it is described as ;
Gas pore is a cavity generally under 1.6 mm in diameter, formed by entrapped gas during solidification of molten metal.

By CWI555

Date 01-29-2008 11:47

Yes it is entrapped gas. However; it ranges from microporosity up to large pores, single pores or clusters.