Dear All,
Why we observe cracking when carbon / low alloy steel electordes is accidently welded on stainless steel butt joints? If
any body has any backup or literature related to this,I humbly request you to post
it.
Thanks and Regards,
Inconel
Cracking of S.S by welding CS or LAS Consumable
Cracking of S.S by welding CS or LAS Consumable
Regards,
Inconel
Inconel
Re: Cracking of S.S by welding CS or LAS Consumable
Welding of stainless steel with carbon steel electrodes results in formation of martensite structure which is prone to cracking under stress or it may crack immediately during welding depending upon the welding conditions, thickness of the part being welded, deposition of consumable etc. But in actual practice, cracks do not come up always. Many a times, welders weld the stainless steel piping with carbon steel in order to avoid the need of purging and they successfully make the weld without any defects that can be picked up in radiography. They weld the root pass with carbon steel consumables and the rest of the welding is made in SS consumable.
However, welding of stainless steel with low alloy steel electrodes would definitely come up with cracking as it is more susceptible to cracking than carbon steel consumables. Same martensite structure formation would occur and LAS consumable being used without any preheating protocol would crack itself during welding mainly due to uncontrolled cooling.
Both of the situations can be seen visually during inspection and one can say that carbon steel or LAS consumable has been used but if gone un-inspected then one may not get it picked with radiography especially in the case of carbon steel consumable, however, LAS consumable has pretty higher chances of getting cracked and picked up.
However, welding of stainless steel with low alloy steel electrodes would definitely come up with cracking as it is more susceptible to cracking than carbon steel consumables. Same martensite structure formation would occur and LAS consumable being used without any preheating protocol would crack itself during welding mainly due to uncontrolled cooling.
Both of the situations can be seen visually during inspection and one can say that carbon steel or LAS consumable has been used but if gone un-inspected then one may not get it picked with radiography especially in the case of carbon steel consumable, however, LAS consumable has pretty higher chances of getting cracked and picked up.
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ashfaqanwer
- Site Moderator
- Posts: 434
- Joined: 16 Mar 2010, 03:36
Re: Cracking of S.S by welding CS or LAS Consumable
Welding metallurgy resulting in using CS consumables on SS is martensite and ferrite in nature which can come up with cracks but with low alloy steel consumables crack would start developing while welding. Now, why with CS cracks doesn't always come up is because of presence of ferrite content which would reduce the chances of cracking. Another reason is that the piping may not be under any load, stress, hinged which may cause martensite structure to give up. Normally, when after the root pass if such joint (CS filler wire on SS) is lifted, it would show up cracking.
What I have experienced at our plant is that on Urea Grade Piping (material SS 316L), contractor used CS filler wire for root pass just to avoid purging during the time of construction. There must be some reduced protocols of inspection / Quality Control at that time which then resulted in extreme corrosion and erosion issues causing heavy thickness loss of weld joints; eventually to be re-welded.
The point is that cracks can come up with CS wire welding on SS but it can go unattended also. Welders do it sometimes and give you a 100% OK radiographed weld joint. Low alloy steels consumables require complete protocol of preheating, interpass temperature and controlled cooling and that's why give cracks when used on SS.
What I have experienced at our plant is that on Urea Grade Piping (material SS 316L), contractor used CS filler wire for root pass just to avoid purging during the time of construction. There must be some reduced protocols of inspection / Quality Control at that time which then resulted in extreme corrosion and erosion issues causing heavy thickness loss of weld joints; eventually to be re-welded.
The point is that cracks can come up with CS wire welding on SS but it can go unattended also. Welders do it sometimes and give you a 100% OK radiographed weld joint. Low alloy steels consumables require complete protocol of preheating, interpass temperature and controlled cooling and that's why give cracks when used on SS.
Ashfaq Anwer
-thepetrostreet.com
-thepetrostreet.com
Re: Cracking of S.S by welding CS or LAS Consumable
During welding of SS with CS welding material, the cracks which are developed are hot ones and can be categorized as solidification cracks as come up during solidification. The main reason of crack development lies in three following factors:
1. Carbon content > 0.1%
2. High sulfur and phosphorus content
3. Low manganese content in the welding region
Presence of sulfur and phosphorus in a weldment which is austenite can produce cracking as sulfur is less soluble in austenite structure (as of SS) as compared to ferrite structure. And when carbon content is also > 0.1% (due to CS welding consumable), sulfur will move towards the grain boundaries of austenite grains promoting weakness and solidification cracking. Manganese tend to reduce the effect of insoluble sulfur but the ratio of Mn/S governs the whole scenario.
However, cracks developed during welding of SS with low alloy steel consumables are hot cracks which come up after solidification during cooling. The main reason is the chemical composition of low alloy steel consumable which when not properly used with all pre-heating, post-heating and controlled cooling procedures comes up with cracking. Silicon and sulfur content in low alloy steels also produce cracking after solidification.
1. Carbon content > 0.1%
2. High sulfur and phosphorus content
3. Low manganese content in the welding region
Presence of sulfur and phosphorus in a weldment which is austenite can produce cracking as sulfur is less soluble in austenite structure (as of SS) as compared to ferrite structure. And when carbon content is also > 0.1% (due to CS welding consumable), sulfur will move towards the grain boundaries of austenite grains promoting weakness and solidification cracking. Manganese tend to reduce the effect of insoluble sulfur but the ratio of Mn/S governs the whole scenario.
However, cracks developed during welding of SS with low alloy steel consumables are hot cracks which come up after solidification during cooling. The main reason is the chemical composition of low alloy steel consumable which when not properly used with all pre-heating, post-heating and controlled cooling procedures comes up with cracking. Silicon and sulfur content in low alloy steels also produce cracking after solidification.