1.4301 welding crack

By yusuf polat Date 02-14-2011 15:50

Dear all,
We are manufacturing cryogenic tanks in our company. At last 4 tanks while cold stretching process welds are cracked at the end of shell longititunal welds. Material is 1.4301 (EN 10028-7) equvalent of 304 stainless steel. We made chemical test on material. At result we saw that sulphur amount in material 0.06%. This is 4 times more than max. amount that standard allows. We sulphur amount couses this problem but we are not sure. Could you please make comments about our problems. Are there anything else we have to check?
Thanks.

By G.S.Crisi (****)

Date 02-14-2011 18:49

I don't understand what you mean by "cold stretching" of a cryogenic equipment.
Let's talk of piping, that's easier to envision. When a piping subject to high temperature service is fabricated at room temperature, a previously calculated gap is left in one or two, rarely three, points. The welding ends where the gap is located must be pulled until the weld can be executed. In this manner, one or two straight runs of piping are shorter than they should be. When the pipe is heated up by the fluid it carries, it expands, and so its length, when in service, is exactly (more or less) its correct length.

Cryogenic service works the opposite way. The piping should be left a little longer than its final length, so when it shrinks due to the cold fluid, its length in service will be exactly (more or less) the correct one.

What I've said of piping applies also to vessels. So, I don't understand why your tanks must be stretched before welding. Their diameter should be a little longer than the design one. Contraction at cryogenic temperature will reduce them to their final value.
Giovanni S. Crisi
Sao Paulo - Brazil

By yusuf polat Date 02-15-2011 06:20

thanks for reply.
Cold stretching is a process that we do on the creyogenic vessels inner tanks. After all weldings done on inner tank we pressurised the inner tanks and make it expand like a baloon. This process have two results. First one is while expanding tanks volume is increases and we have bigger tank with less material. second one is while expanding tanks material passes the yield strengh point and material strength increases. All this process are aplicated before cooling the tank for cryogenic service. Tanks temperature is ~20°C.
All WPS and PQRs are checked and no mistake on them. We checked the welders while they are welding there is no problem. We done this process and tanks many times before but this is the first time we had this kind of problem. Everything is good on tank just the end of the longititunal welds of shell cracks.

By ravi theCobra (**)

Date 02-15-2011 18:01

Way back when in the 1960's the company I worked for made stretched tanks. We used a modified 301 alloy and then pumped in liquid nitrogen. With about 15 % elongation we got between 275,ooo and 290,000 tensile strength at room
temperature due to the retained martensite at room temperature. The stainless was a "tweaked" version of 301.

Are you folks using a T 304 deritive ?

By yusuf polat Date 02-18-2011 06:32

we are using 1.4301 stainless steel according to european norms. It is equvalent of 304 stainless steel. 621MPa UTS, 290MPa 0,2%Yield at room temperature.Chemical compositions are nearly same.