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Up Topic Welding Industry / General Welding Discussion / Welding Stainless To "Regular" Steel
- - By poolownerinnyc Date 03-24-2004 14:56
I manage two commerical steel pools in NYC. The main drain boxes are allways a pain in the neck when we start the pools. There are 2 inch taps in the boxes that are plugged during the summer and have hydrostats in the winter. These taps allways rust causing a headache. I would like to have the boxes replaced preferably with stainless steel. The question is can you weld "regular" steel to new stainless drain boxes ?
Parent - - By Bill A (**) Date 03-24-2004 15:28
Welding stainless to mild steel is common. The most commonly used filler metals are Type 309 or Type 312 stainless.

There is the possibility for accelerated corrosion on the steel side of the steel+stainless weld joint caused by the connection between the dissimilar metals. If a cathodic protection system is installed (assuming this component is buried) it will prevent that corrosion. If there is no CP then the best way to minimize the possibility of galvanic corrosion is to coat the stainless steel (i.e., minimize the cathode area in the anode/cathode pair).
Parent - - By poolownerinnyc Date 03-24-2004 15:37
Thank you for your response, next question, what is and how would a cathodic protection system be installed. The top side of the drain box stainless" would be painted with an epoxy pool coating, the bottom or underside of the box would be in direct contact with the earth as so with the plate "mild steel" on the bottom of the pool.

TYIA
Parent - By Bill A (**) Date 03-24-2004 20:22
you might want to consider posting the question about C.P. on the following site frequented by corrosion engineers, some of whom are more knowledgeable about CP: http://www.eng-tips.com/threadminder.cfm?spid=338
In general, CP consists of connecting the structure to be protected to either a "sacrificial anode" (such as a hunk of magnesium or zinc that freely corrodes) or to an impressed current anode that is connected to a rectifier. In either case, the anode supplies a very small amount of current to the structure (the pool in this case) which alters the voltage or potential between the structure and the soil, with the result that corrosion is prevented. However, the selection of the anode material and the details of the CP design depend on a bunch of factors such as the surface area to be protected, the soil resistivity, the distance from the anode to the structure, etc. Designs are best left to an experienced corrosion engineer. Be aware that generally it is not good practice to depend only upon a corrosion resistant paint or coating to prevent corrosion of buried steel. There will always be some break or flaw in the coating and the C.P. is designed to protect those flawed areas from corroding. C.P. is used in potoable water tanks, too, but I don't know if it is practical for the inside surfaces of a pool.

A good example of C.P. is the use of anodes in domestic water heaters. Eventually the anodes get consumed by corrosion, as they are intended to do, and need to be replaced to maintain effectiveness, but a properly designed CP system can last a long time with minimal maintenance.
Parent - By ssbn727 (*****) Date 03-25-2004 08:04
Hi Poolownerinnyc!
Small world! I'm originally from NYC (born in Manhattan but, lived most of the time in Queens) also and currently reside in Pittsburgh, PA because I needed a liver transplant over six years ago and have been living here since...
Anywho, you're getting some good advice here from Bill A about the corrosion problems you're experiencing... As Bill A mentioned, Cathodic protection is definitely the way to go with your application if you're main concern is to minimize the amount of maintenance required for your pools. I would also agree with Bill A's recommendation to use a 309 or a 312 stainless filler for the welds... The complexity of the variables involved with your situation, does'nt enable you to come up with a simple fix to your problem and I can only guess that you're looking for a one time permanent solution to this yearly maintenance problem...

After re-reading your situation I've got a few questions but I'll ask this one first; Is the rest of the underside (also making contact with the ground?) mild steel surface of the pool uncoated completely (I hope not!) or is it uncoated just within the immediate area where the drain is located? Is there a moisture barrier of some sort that you are aware of underneath the pool also? I only ask this because, I want to make sure that you do'nt have a bigger problem on the horizon and eliminate that possibility in my head...
Also, may I ask where in NYC are these pools located?
I'm going to visit the "Big Apple" soon so if you'd like, I could take a closer look at your situation when I'm in town... You can find my e-mail by clicking my blue colored forum name: "ssbn727" and then I could give you more info on how to contact me by phone. I look foward to hearing from you soon.

"REMEMBER 9-11-01 MOST OF ALL - NEVER FORGET!!!"

Respectfully,
SSBN727 Run Silent... Run Deep!!!
Up Topic Welding Industry / General Welding Discussion / Welding Stainless To "Regular" Steel

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