Welding Joint Made at Site in Hot-dipped Galvanized Line (Vent Air Line)

It depends on how clean and dry the vent air is.

What alternatives, if any, were available to the subcontractor for making this branch?

We are not having any alternative and we were unavailable while branching but now condition says to take approval from client with valuable feedback. so i'm with experts

This forum isn't your client. Did you talk to your client, and what did he/she say, Mildred?

Forum is not a client but importance of forum & given references is more than client,

Iron is a fairly active metal and corrodes readily in the presence of water (moisture) and corrosion rate is enhanced by an electrochemical process in which water becomes an electrolyte, it is electrochemistry concepts.

In our case, vent air of ABS product (acrylonitrile butadiene styrene) which is in dry powder state,So we can say there is no electrolyte to transfer electrons and ions, no need to worry about corrosion

That may be true, and desirable to convince the client. But then, why was the vent line designed as galvanized in the first place? External corrosion only, perhaps?

Correct, i was also surprised but i'm not from engineering to design. Thanks a lot for your references about dryness as you hint previously

As this project is presented to us, the need for galvanizing is the least of your worries. "Vent air of ABS product (acrylonitrile butadiene styrene) which is in dry powder state" is a much greater concern than you have stated in the above. Unless there is an appropriate filter to capture those particles such as a scrubber, bag house collector or some other type of entrapment for the particles and vapors this is going to be a very large source of pollution to personnel and the atmosphere. Although it had very low health hazards, according to SARA Title III, Section 311/312, Health Hazards, it is an immediate health risk and a delayed health hazard.

Unless something is done to capture the particles and the vapors the company operating this site could be in for some fines or other problems. In the USA this certainly would not be tolerated and would probably generate summonses with large fines until fixed.

Good Luck, Old Salt

Chop out the section, weld on some flanges, weld on the branch, then galvanise the lot before reassembly, with bolts.

Your client needs lots of help.

He has obviously hire an incompetent company to fabricate his equipment.

To suggest that this client would take the recommendations of total, unqualified strangers from an anonymous forum speaks volumes about their lack of technical sophistication, and yours.

You own it to your client to commission a QUALIFIED engineer to evaluate the problem and direct the remediation, or justification, for this poor planning and execution of the piping and process design.

What is the name of your company?

If this seems harsh..........................................

That is too harsh. Glitches happen on project installations. Lawyers, bureaucrats, financial people, and safety nazis are seldom helpful in ameliorating matters.

At one extreme, Crabtree has given a valid, but perhaps overkill, solution. Galvanized design can be quite tricky, and modifications even more so, as seen here.

For outsiders like us to evaluate this fully, we would need the contract documents, especially as related to variances, repairs, etc.

Perhaps, but the evidence says otherwise.

OP says, "The issue is for damages made while branch welding and there is no option to repair the coating from inside"

If this was not a planned penetration, with proper forethought, then it is an unauthorized deviation from the documentation, if there ever was any.

Adeel Ahmad has been caught, unaware apparently, that this problem has now come to light.

The question posed here is "how to justify the "damages" (OP's words, not mine) not how to fix the problem.

I admit that not being there we have no way of knowing what is really in the air inside the 12" pipe. All the more reason to commission local experts, not an anonymous forum.

OP, in post #4 provides the ONLY possible justification for doing nothing. Can he justify it?

Otherwise the thread is devoid of any useful information.

Glitches happen, of course, but making excuses for them based on anonymous stranger's uninformed opinions is not professional.

I stand firmly behind my initial response.

I think the reference to "damages" is literal, damage to the vent, not the type that involves lawyers.

The people who specified that it be galvanized should be asked why they specified it, if it is absolutely necessary or just a precaution.

When the option of Wrong Answer or Bad Answer is offered, then no one will be obliged to use Off Topic as a substitute. In the meantime, live with it.

I don't feel that my answer was either wrong, bad or off topic, but I support your right to vote as you see fit.

Harsh? Of course it was. It was meant to be.

Who's minding the store here?

As I have said many times before, if I were a client with millions of $ invested in a project and my contractor came to me and said, "We have discovered a problem with our fabrication methods, but after consultation with numerous anonymous, on line experts, (who have absolutely no information to use), we have decided that it is OK to continue with the non-complying plumbing system."

Trust me!

If the customer has specified Galvanized duct - he would not accept in first place a discoloured welded patch on same.

Your reason to find out opinion indicates that Client is not accepting welded patch which is not galvanized.

Possible solutions are:

1. If the piece of duct between bolted joints is not very large that it can not be handled in molten bath of galvanizing plant, get it galvanized again.

2. If the duct is relatively larger in size then the possibility is that in stead of Hot Dipped galvanizing, previously also sprayed with Molten Zinc. This is common practice on large sized which can not be accommodated in Zinc Bath or thin sections such as ducts which will distort if dipped in a bath.

Hot galvanized spray is a portable equipment consists of coil of zinc, a oxy-acetylene torch which continuously melts and sprays molten zinc on surface it is directed. Most probably the duct you had supplied also was sprayed by supplier with similar equipment.

Hot Zinc or Aluminium spray is common practice in chemical plants, depending on operating temperature. For example hot flue gas duct of Engines are sprayed with hot Aluminum.

Pl find contractor doing similar job, he will do abrasive cleaning of effected area and spray with zinc spray restoring it to original.

Zinc Colloidal paints are also available, these are fine around drilled holes or very small tag weld, one or two of 1cm but not for your case and again customer may not accept same.

By digging seriously I've found some more details and these are..........

According to material specification It has to be fabricated with galvanized sheet, welded at site and it has to be coated with zinc rich primer externally, no need inside coating because these lines are no process lines and it is vent only, Operating pressure for these lines are varies from -0,03 bar to 0,02 bar. The required structural thickness for these ducts is 3 mm, note that my company has purchased CS pipe with thickness between 5 to 8mm and calculated the span life in the worst possible scenario noting that the fluid is: non-compressed air containing corrosive dust and considering a CORROSION RATE of: CR = 0,0927 mm I year

Now come according to NACE publication,

Therefore my company is supplying a minimum corrosion allowance of 21.5 years considering a corrosion allowance of 2 mm in the worst conservative scenario and a total life of more than 50 years. So we are supplying a corrosion thickness that are Improving the final span life of the vent ducts.

It's my understanding that my company is proposing a more reliable solution, as I've not seen yet companies in the world looses their money like this.

Thanks a lot for experts opinion, more or less above sentences are enough to convince client's quality team

Please see your first post. "HOT DIPPED galvanized" AND NOW IT IS "CARBON STEEL PIPE OF 5mm THICKNESS AGAINST 3mm SPECIFIED". Why do not you do your full home work than wasting our time in asking suggestions.

Mr. Adeel Ahmad, do not of others' impression, but I shall be last to reply to your posts in future.

Yes I have seen my post and fully aware that we are supplying the CS materials to other party for hot-dip galvanization.

Read again the thickness shown to calculate span life. Sorry to say that your solution is against of your name Mr.Powersolution.

that last sentence makes no sense to me.