Welding Defect 1

[baski67]

Dear all
Large number of minor Cracks of 5 to 10mm (Not visible in Co 60 Radiograhy)while Gauging few locations in carbon steel casting (WCB) of large section thickness 150 to 170mm. Number of cracks increases while gouging

Can anyone throw light on this behaviour?
How to handle / salvage ?

 

[GRoberts]

It sounds like a problem we encounter occasionally when we get microshrink underneath a riser. The microshrink will keep the casting cracking until it is completely removed. It provides initiation sites for these small cracks you are experiencing. The times I have seen this, it has been under a very large riser, so the hole that ends up being gouged out can be very large. We normally keep excavating until we can get a clear hole with LPE or MPE, then decide if the casting is worth saving or not.

 

[baski67]

Thank you for your response.

The subject casting is Taper Plug Valve Body.
Though there is a belly riser, the defects are spreading all thro the thickness much away from the riser also.
When we weld , we notice crack at the joining layer with the parent metal also. We have seen crack on the opposite side to rise also. We feel it is not related to the riser leffect. Pl advise.Regards

 

[GRoberts]

All I can say, is that most of the time, especially with mild steel castings, cracking is related to some sort of defect such as microshrink, hot tears, gas, etc. If you don't get out all of the defects, cracks usually propogate through the weld later. Keep arcing until you can get a hole that is MT &/or UT clear before repair welding.

 

[huzoor]

any one tell me what is abbreviation of wcb means for astm a-216 grade wcb.

huzoor bux leghari
mechanical engineer

 

[metengr]

See thread330-139571

 

[arunmrao]

Have you checked the carbon?If the carbon is above 0.25% and also check S & P levels. Grinding cracks gas cutting cracks begin to appear. They are not related to risering. Anneal the casting and then do your cleaning .These cracks are so fine that they go undetected in radiography. .

 

[arunmrao]

In heavy section thickness segregation can be a problem. Homogenizing the casting before gas cutting and grinding will eliminate the defect.

Pl let us know if it helps.

 

[ibf]

Besides all of the above good recommendations, make sure you pre-heat the casting , or at least the excavated zones prior to welding. Control interpass temperature and also PWHT in accordance with the W.P.S & P.Q.R (if any).

 

[HgTX]

Y'all do notice, do you not, that the original question is from 2002 and the thread was only re-awakened by someone asking about an abbreviation in the initial post?

Hg

Eng-Tips policies: faq731-376

 

[lewtam]

All hail...the dead post is risen.

LewTam Inc.
Petrophysicist, Leading Hand, Natural Horseman, Prickle Farmer, Crack Shot, Venerable Yogi.

 

[arunmrao]

another example of post submittal blues. I failed to notice the original date and then continued with the thread.It is only now HgTX pointed out the error. A dead horse brought alive!

 

[HgTX]

Not that this isn't plenty educational 'n' all. I personally don't mind undead threads. Just as long as y'all know that the target of your advice is more likely to be a future someone searching Eng-Tips, rather than the original poster.

Hg

Eng-Tips policies: faq731-376