Stainless steel tank welding

Date 07-21-2011 19:34

Really not enough info, Bootleg.

If tank is carbon steel you should be using carbon filler metal.

What process? SMAW, GMAW, GTAW?

By BooTLeG (*)

Date 07-21-2011 20:14

GTAW the tank is carbon steel...the plate is carbon steel...i thought by using a stainless rod it would be a much stronger weld then simply a carbon rod...basically i have welded a coupler on a tank 3 times and it is still getting a crack in it after they put fuel in it.

By qcrobert (***)

Date 07-21-2011 20:44 Edited 07-21-2011 22:00

When necessary to join stainless to carbon the recommended rod is ER309 because it has a higher carbon content (0.12) than other stainless rods. This enables the resulting joint to be more diluted and not have an abrupt boundary of ss to carbon.

Anyway, it would have been best to use ER70S-X to make the repair. Because there is ss in the repair I do not believe it can be removed at this time.

Btw, I am no expert by no means when is comes to repairs of this nature, heck gas tanks are the worst because they are difficult to clean for the repair.

IMHO I would try to clean the area up, make sure there is no porosity, oil, gas for sure, etc and then reweld with ER70S-X. In a bind I have used a metal coat hanger for the filler wire but who has any thing but plastic ones now.

After repair and before filling back up with gasoline, seal off the tank, fill with water, and pressure up to 5 psig. You will need to fab a Tee fitting with gauge and relief vent. Remember household water pressure is 60-80 psig and don't wish to go near that high. Get a spray bottle filled with water and a little dab of dish detergent to spray on the area in question, bubbles will appear if leaks are present.

Wish I could help more,
QCRobert

By BooTLeG (*)

Date 07-21-2011 22:34

Well that is definantly more information then I knew...the only problem its a double wall 40000 gallon tank and it is leaking into the interstitial space so pressuring it up is not possible due to the chance of imploding or damaging the inner tank I pulled 7 inches of mercury by a vacuum and left it for an hour and there was no change so I told them to put fuel in it and it leaks within a week

By DaveBoyer (*****)

Date 07-22-2011 01:18

Does this mean that You are welding the coupler to both the inner and outer tank walls?

Does the the inner tank wall flex while the tank is in use?

7" Hg creats a pressure diferential of nearly 4 PSIG. I am curious, are You pulling the 7" on the space between the tank walls? How much do the walls distort when You do that?

By BooTLeG (*)

Date 07-22-2011 02:15

I am welding on the inside tank to try and keep it from leaking to the outer tank...the ends of the outside tank are bowing in due to engineering inadequacy when it was built but pop back out when air gets back into it but no visible change to the inner tank...Charlie this is the fourth time it's been welded on first time was two 7018 passes over the crack and still welded so me and my boss came up with a carbon plate over the crack and stainless steel weld over for more support

By dbigkahunna (****)

Date 07-23-2011 01:20

First, Is this a UL 142 tank?
The proper way to fix this, and I am guessing it is a bottom connection, is to remove the nozzle completely and install a new nozzle. This will involve removing a portion of the outer shell where you can get access to the back side of the nozzle.
This will need to be roughly 12 inches square. The smaller the better and if the nozzle is close to the "knuckle" you will need to be aware of weld spacing. However if this is a UL 142 tank, maintaining weld spacing is irrelevant as the tank is no longer a UL142 Standard Tank. More on this later.
Cut out the entire nipple and replace with new Sch 80 pipe.Weld the inside, SMAW with E6010 two pass minimum. Let it cool.
Spray diesel on the outside and let it sit for a minimum of 8 hours, overnight would be better.
Visually inspect the weld and if there is no indication(s) clean the diesel off and weld the outside.
If this is a horizontal tank pressure up the tank to 3 PSI minimum to 5 PSI maximum. Have a 10 PSI gauge with quarter pound increments. If it is a hot day, watch the pressure closely. Have a 5.5 PSI pressure relief on the tank. If this is a vertical tank, rather uncommon for double wall but, have the pressure 1.5 minimum PSI with 3 PSI max and pressure relief at 3 PSI max.
When the tank is at pressure, apply a soap solution to the weld. If there are no indications release the pressure.
Weld a lap patch over the area you cut out for access to the nozzle . If the toe of the patch is within 3 inches of the tank "knuckle" you will have to replace the "knuckle". After welding the lap patch, vacuum test at 7-10 inches vacuum and hold for 24 hours with loss of no more than 2" in 24 hours allowed.
The deformation you see when you pull a vacuum is normal and necessary. Or stuff breaks!
Now the bad news for the owner. While this repair will make the tank capable of holding liquid, it can no longer be considered a UL 142 tank. This means the owner cannot legally sell the tank as a UL 142 tank because of the repairs.
This is no skin off you, as you are only doing what the customer wants. But when the required inspection of the tank is done and the inspector sees the repairs, the owner has no documentation for proper welding procedures or qualification of the welder.
STI has SP 031 Standard for Repair of Shop Fabricated Aboveground Tanks for the Storage of Flammable and Combustible Liquids spells out the extent, requirements and limitations of repairing these tanks and R912 Installation Instructions for Shop Fabricated Stationary Aboveground Storage Tanks for Flammable, Combustible Liquids gives the testing and pressure limits for pneumatically testing these types of tanks.

By BooTLeG (*)

Date 07-26-2011 21:48

Thank you kahuna you seem to know exactly what I am talking about...what is the advantage of making an arc weld vs. Using a tig weld minus the cost and time is there any difference in strength, or is there a reason not to use the tig setup

By dbigkahunna (****)

Date 07-28-2011 03:47

You are gaining nothing using GTAW instead of SMAW. 5P is all it needs. And because of the thin material, stay away from 7018.
These tanks are made from A36 material so a 60,000 rod is more than sufficient.
Is there a manway where you can get inside the tank to weld the backside of the new nozzle?

By BooTLeG (*)

Date 08-01-2011 14:44

yes there is a manway to get into the inner part of the tank that is where we have been welding it and it keeps cracking so i am probably going with cutting it out and using a schedule 80 part like you were saying

By dbigkahunna (****)

Date 08-02-2011 01:00

Need any thing let me know.

By BooTLeG (*)

Date 08-12-2011 19:27

When you say "knuckle" does that mean the weld seams or the end cap welds? Also after I cut out the outside portion of the tank your saying weld the outside part of the inner tank then spray diesel fuel from the outside? If this is so what is reason for the diesel fuel? Thank you again for the help you have given me.

By dbigkahunna (****)

Date 08-13-2011 00:31

The "knuckle" is the rounded area on the end cap.
You want to be sure the weld is seal welded with no leaks.. Do not spray the diesel on the inside where you may have to fix a pinhole if there is a indication. Spray it on the outside and look on the inside. If there is not leaking in the inside, complete the weld on the outside against the shell

By elisagrace Date 09-28-2016 11:07

I am replying this today as I am in similar situation today. I have used all the techniques mentioned by you but none of the formula was fitted . Later on I took the advice of one of my friend who is working as supervisor in industrial tank manufacturing unit here http://www.greatbasinindustrial.com/industrial-tanks-and-storage told me that, the best way to repair this tank is by removing rust part and to fix new piece there by way of welding, I followed this and my problem was solved.