316L SS - Materials science: Pickle and Passivated versus bright annealing 3

[hondashadow1100vt]

I am a PE working on a construction project. Our specifications call for all 316L stainless steel piping to be pickled and passivated. Our contractor has proposed one manufacturer that can furnish all the piping for the project, however the manufacturer uses both the pickle and passivation process as well as the bright annealing process to prepare the piping. The manufacturer claims that they cannot furnish all of the piping with only the pickled and passivated treatment. I am trying to make a fact based determination of whether or nor the bright annealing process is technically equivalent to the pickle and passivation process. The purpose of this thread is to request information/insights/feedback on the subject of these two treatments.

I am specifically thinking that a technical substantiation would include the following:
1. What is the intent of the pickle and passivation process? Is the intent of the bright annealing process the same or somewhat different?
2. How is the pickle and passivation process’s effectiveness is measured? What test is available? What data can prove it?
3. How the bright annealing process’s effectiveness is measured. What test is available? What data can prove it?
4. Relative qualitative cost difference (if any)

Thank you in advance for any feedback that you may be able to provide!

 

[EdStainless]

1. P&P usually follows an oxide anneal (in air). The pickle removes the surface oxides and some base metal, the passivation assures a clean surface. It leaves a soft finish (not super smooth and bright) that is white looking.
This is the cleanest surface possible.
2. There are simple tests for free iron on the surface. On P&P product you have to have visible scale patches to fail them.
A better test is measuring the corrosion potential electrochemically, but there is no standard for this.
3. A BA finish is only as good as the dew point of the furnace and the handling after it is annealed.

If anyone touches these parts with a steel tool at any point during fabrication, transport, or erection then they should be passivated in place afterward, or you will get rust spots from the flakes of imbedded iron.

It can be difficult to P&P very small diameter tubes since it is hard to get solution down the ID uniformly.
We choose P&P vs BA based on the surface finish desired by the customer. They look very different.

One option that is often seen in architecture is to mechanically finish all tubes and then passivate. This way everything will have the same polish pattern. This does cost a bit more, but gives reliable uniform results.

I do hope that these pieces will not see any exposure to salt, either deicing or from being near the coast. 316 will not stand up to that long term unless it is regularly washed by rain.

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Plymouth Tube

 

[Duwe6]

If you find that the "P&P" is for corrosion and/or pitting resistance of the ID, plan on passivation AFTER the system is complete. All welds done, hydro test complete. ASSuming that previously passivated pipe is still perfect after months of mechanical work, rigging & hoisting, WELDING, and stray tool strikes is a very bad idea.

My personal preference when ID pickled pipe is necessary is to just buy 1st World materials [USA, EU, Scandinavia, Japan] to standard ASME spec & grade. Emphasize in-process cleanliness to the field craft, by actually hiring and using QC/Welding inspectors during 100% of the work, by rewarding and disciplining the welders, fitters, and foremen based on performance. A [small, even] reward for 'getting it right' goes a long way towards proving that you REALLY mean that something is important to the project.

As part of the hydro process, flush each section, pressure test it, and passivate it. Spend your money in the middle of the project [workman-like cleanliness during construction] and at the end. Not really possible for "P&P" pipe to survive construction w/welding 'intact'. The welds are unpassivated, especially the HAZ - heat affected zone. The pipe and fittings are going to get dirty, dinged, rubbed by carbon steel items, etc. Waste of money to spend it before the job is essentially complete.

 

[EdStainless]

Are these process (flow) lines or is this an architectural application?
In the first case you are worried about both OD & ID, in the second just the OD matters.

1. Any welds need to be pickled using paste.
2. The SS should be wrapped or covered with plastic or paper during handling and erection.
This also makes it more obvious how badly they have been mishandled.

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Plymouth Tube

 

[MagBen]

Manufactures normally donot do passivation, as pointed out, it is a kind of waste passivating at this stage.

Bright annealing is normally done for strip products, not for bars.

Purchasers could order oxidizing annealed as is, or finish turned without pickling even after non-bright annealing.

Tests are often performed to evaluate the surface of passivated parts. The question to be answered is, "Did passivation remove free iron and optimize the corrosion resistance of the free-machining grades?" It is important that the test method be matched to the grade under evaluation. A test that is too severe will fail perfectly good material, while one that is too lenient will allow unsatisfactory parts to pass.

A faster method is available using a solution from ASTM A380, "Standard Recommended Practice for Cleaning and Descaling Stainless Steel Parts, Equipment and Systems."

 

[MagBen]

for bright anneal, we check the color of the surface recording the Delta "L', "A" and "B" values. If failed, an acid cleaning operation will be done to clean the heat tint.

 

[EdStainless]

Ben, how about removing oxide films that degraded corrosion resistance but don't have a color?
How do you quantify the colors? electronic measurement or reference cards?

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Plymouth Tube

 

[EdStainless]

I'll go ahead and add that there is a very effective and easy test for residual free surface iron.
1. Find some WHITE Head & Shoulders shampoo
2. Brush a thin layer on the surface
3. Mist with DI water to keep it hydrated
Within 15-20 min you will start seeing blue spots if there is free Fe.

This is why some H&S is dyed blue, because it is made in plants with some CS piping.
The active ingredient will complex with Fe and turn blue.
So in those locations they color it so that it look consistent.

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Plymouth Tube

 

[hondashadow1100vt]

EdStainless:
Thank you for the explanation of the pickle and passivation process (Ref. 6 Dec 14 1:24 post). I have a couple of follow-up questions:
A. Is it fair to say that the visible scale can be “spot” pickle and passivated in the field after installation? It sounds like this is possible based on your follow-up comment regarding “…passivated in place afterward…”.
B. Based on your note that the “BA is only as good as the dew point of the furnace and the handling after it is annealed”, is it fair to say that the bright annealing process produces a finish that is somewhat inferior to a pickle and passivated finish? Can a bright annealed process be field repaired on the construction site after installation? Can the factory bright annealed finished piping be repaired with the field pickle and passivation process?
I suspect that the installed piping will be handled with various metallic tools, etc. throughout the installation process therefore field repairs will be necessary.
(This project is not concerned with the appearance of the piping, only the performance of the piping.)
These pipes will be exposed to salt due to the fact that the piping will be conveying a product that is basically a refined waste glycerol (derived from the biodiesel production process). The product includes a salt that helps to prevent microbes from eating the fluid (which has a high caloric value) and forming a slime layer within the piping system. I will noted that the experience in my industry is that 304 SS experiences pitting corrosion but that 316 SS tends to stand up reasonably well to this service. The piping will be installed in a marine environment but it is not a highly saline environment.

 

[hondashadow1100vt]

Duwe6:
The “P&P” is intended for corrosion and/or pitting resistance of the ID of the pipe. That is the side of the pipe that would not normally be subject to mechanical tools, etc. Note: The piping is almost entirely comprised of grooved joints and press fit joint systems therefore the piping will undergo almost no welding.
How can passivation be performed following the installation of the piping?
Normally a hydro test is performed immediately prior to charging the system with the final working fluid/product. I am not sure that I have heard of a project where a final “P&P” is done just prior to adding the intended fluid product. I admittedly don’t know if the “P&P” fluids are chemically reactive with the “P&P” chemicals.
The piping will be 100% comprised of piping manufactured in the United States.
I will emphasize to the project’s construction management inspectors that the mid-project cleanliness of install and mid-project “P&P” is important. Is there a recognized standard that can be adhered to that describes installation quality standards that can be adhered to in order to make this enforceable?
I thank you kindly for your thoughtful insights.

 

[hondashadow1100vt]

EdStainless:
Thank you again for your input. I really appreciate it. The following is in regards to your 8 Dec 14, 1:05 pm post.
These pipes are process (flow) pipes, not architectural.
1. It sounds like pickling paste is the type of product to apply after installation in order to correct defects that result from the install process. This is helpful.
2. Is there a nationally recognized installation standard that you are aware of that calls for wrapping or covering piping in plastic or paper during the installation process?
Thank you again!

 

[hondashadow1100vt]

MagBen:
The product is piping. I don’t know that I understand what is meant by “strip products” versus “bars”.
The grade of stainless steel under evaluation is 316 SS and 316L SS.
Thank you for referring me to the ASTM standard. I will make some time to look up and read through that standard.
Thank you for your interest and expertise.

 

[hondashadow1100vt]

MagBen:
Regarding your 8 Dec 14 18:05 post: Are the Delta “L”, “A” and “B” values parameters that are described within the ASTM A380 Standard Recommended Practice for Cleaning and Descaling Stainless Steel Parts, Equipment and Systems”?
If so, I gather that I will understand better once I pull and read the standard. If not, then what are these parameters?
Thank you again.

 

[EdStainless]

Honda,
1. The best pickling paste that I know of is called RedOne.
Since it contains Fl it must be rinsed very thoroughly, but it works.
2. I don't know of any standard for covering SS piping during handling and erection. We have a customer that has his own requirements for this. He uses paper if the job is under roof, and plastic if it is out doors.

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Plymouth Tube

 

[Duwe6]

To passivate after construction of a pipe system, a warm 'pickling' solution is circulated in the system for a couple of hours. This is typically handled by a contractor that specializes in this work. And make sure that when/if you hire them that their scope-of-work includes disposal of the spent solution.

 

[MagBen]

We use a spectrophotometer to measure color: L* defines lightness, A* denotes the red/green value and B* the yellow/blue value. LAB values are only our internal limits, only to check the appearance, or qualify the bright anneal to some degree (dew point, furnace condition).

Grinding off the heat tint could degrade the corosion resistance which is not taken into consideration.

Strip, bar, billet etc. are product forms.

 

[EdStainless]

Ben, We often split tubes and pickle one end. The BA and pickled surfaces should look the same.
We tested a couple of color measurement devices, never found one that would handle such bright surfaces reliably.

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Plymouth Tube