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Need To Design A Simple Phosphating System for Machine Shop

Q. Dear All,

My name is Joseph and I am a Quality Engineer in a Machine Shop.

I have a challenge to design a simple phosphating system for our machine shop that will be used to phosphate API thread connections and other finished products, but I do not know how to begin or what to do.

Should it be Zinc or Magnesium phosphate? Which is better, cheaper and easier? What are the names of phosphating chemicals? What is the list of equipment needed? The system should have a means or reading temperature of the bath. How do I do the titration (correct acid mixture)?. How do I measure the thickness of the phosphate? The system should meet API Spec 7-1 standard.

Does anyone have an idea? I will be grateful if I can have a detailed procedure and layout that meets API standard. Please I need help. Please I need every information.

Thanks everyone

Joseph Akparawa
Machine Shop Quality Engineer - Port Harcourt, Rivers State, Nigeria
May 12, 2010

"Phosphating of Metals"
by Werner Rausch

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"Phosphating & Metal Pretreatment"
by D.B. Freeman

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(affil links)

May 13, 2010

A. Joseph,
This literally takes a small book to answer.
Step 1 is to get a copy of the specification (with all reference specs) and see what they require.

Very probably, it will be a zinc phosphate, but there are several formulations for different grain sizes.

Step 2 would be to contact all of the vendors of the zinc phosphate solution that you need to use.

The possible vendors can provide you with all of the information that you need to run the line as well as most of them will have one or more equipment vendors that they like to recommend.

The secret to running a good phosphate line is to follow the instructions -- exactly -- and to always have a load in the tank as soon as it gets to operating temperature. This will allow it to keep the acid ratio exactly where you need it to be. I always made a water addition to the tank after the last load came out to drop the temperature rapidly. You will make several water additions throughout the day because of the evaporation resulting from the high temperature.

The vendor will train your people on how to do the titrations. If not, find a better vendor.

James Watts
- Navarre, Florida

Q. Is zinc phosphating mandatory in workshop business if a connection is recut?

What is the document reference for that?

Is it possible to receive a copy?



Osama Hijazi
- abu dhabi, UAE
September 26, 2012

A. Hi Osama.

Unfortunately we don't have enough information to understand your situation.

I don't really know what you mean by a connection being "recut". If this is painted steel and you have exposed bare steel, it probably should be pretreated before painting. To my knowledge there are no "universal" rules; so using a primer instead of phosphating may be sufficient. But depending on what business you are in, and what service you are providing, they may be specific rules or codes that affect you ... but we don't know your situation.

If your question is a follow-up on Joseph's question about API requirements for re-threading a threaded joint, I would assume that re-phosphating is necessary. But you would need to get a copy of the API specification as James suggests. I'm sure this is copyrighted and must be purchased; people would not be allowed to send you a copy of their copy. I am not from the petroleum industry, so I am not familiar with API codes; but from the title of the specs, I'd probably start with API 570 [affil link] "Piping Inspection Code: Inspection, Repair, Alteration, and Rerating of In-Service Piping Systems". Best of luck.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
September 26, 2012

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