welding of SS 304

[Hang Suin]

Since I have to weld SS 304 piping, I have been advised that it shall be welded using SS 308 filler rod. Could one tell me why I cannot use SS 304 filler rod for such a welding? Can I use SS 316 filler rod for performing the welding?

[Hollan Petersen]

Since there are a number of grades that have similar properties like SS 302, SS 303 and SS 304 the companies that produce welding consumables prefer to manufacture the SS 308 consumable in order to weld not only the above referred grades but also the SS 308. As far as your question is concerned, simply I could say that since the base material is picked for purpose then the filler metal should match the base material and moreover it shall not alter its chemical performance.

Given that the SS 308 is 19/10 (19%Cr, 10%Ni) and the SS 304 is 18/8, then we realize that there is a little more Cr and Ni in SS 308 and thus it helps keep the ferrite content under control in the molten puddle and help prevent hot cracking. Instead, using SS 316 (16%Cr, 10%Ni, 2%Mo) filler metal for welding SS 304 base metal it is made clear that a part of chrome is being lost since an amount of molybdenum is being induced. Moreover, I would like to add that you shall avoid the usage of SS 316 filler metal in certain corrosive environments that cause metal dusting (http://en.wikipedia.org/wiki/Metal_dusting) of SS 316 (eg, mixture of CO, H2, H2O, CO2 and CH4 in the temperatures higher than 400°C).

For more information with respect to this topic please have a look to the below link:
http://www.ssina.com/download_a_file/weldingbook.pdf

[Logosweld]

Stainless is easy to weld but very difficult to keep flat, the coefficient of linear expansion is 1.7 times that of mild steel
304 and 316 (as opposed to the L low carbon versions) suffer from weld decay. When heated to welding temperatures the Chromium combines with the Carbon leaving the steel short of Chromium and therefore unable to self repair itself.
This was virtually eliminated by introducing stabilised stainless steels 347 and 321 which contain Niobium or Titanium which sacrifices itself to save the Chromium, however, when lower carbon versions 304L and 316L were introduced the problem of weld decay was eliminated.

[Logosweld]

Since there are a number of grades that have similar properties like SS 302, SS 303 and SS 304 the companies that produce welding consumables prefer to manufacture the SS 308 consumable in order to weld not only the above referred grades but also the SS 308. As far as your question is concerned, simply I could say that since the base material is picked for purpose then the filler metal should match the base material and moreover it shall not alter its chemical performance.

Given that the SS 308 is 19/10 (19%Cr, 10%Ni) and the SS 304 is 18/8, then we realize that there is a little more Cr and Ni in SS 308 and thus it helps keep the ferrite content under control in the molten puddle and help prevent hot cracking. Instead, using SS 316 (16%Cr, 10%Ni, 2%Mo) filler metal for welding SS 304 base metal it is made clear that a part of chrome is being lost since an amount of molybdenum is being induced. Moreover, I would like to add that you shall avoid the usage of SS 316 filler metal in certain corrosive environments that cause metal dusting (http://en.wikipedia.org/wiki/Metal_dusting) of SS 316 (eg, mixture of CO, H2, H2O, CO2 and CH4 in the temperatures higher than 400°C).

For more information with respect to this topic please have a look to the below link:
http://www.ssina.com/download_a_file/weldingbook.pdf

nice that sounds good..