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zanba
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Join Date: May 2012
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Material Selection for the Gas (NH3+H2O+Co2)

06/24/2012 7:15 AM

Hi guys

We want to select a sufficient material for exchanger which the gas (NH3+H2O+Co2) with pH=13.7 and 900c is passed.

We have 2 selection: 1. SS316, 2. Carbon steel with PVDF coating

Which one is better?

Please help me with strong reason.

Thank you so much
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Crabtree
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#1

Re: material selection for the gas (NH3+H2O+Co2)

06/24/2012 9:14 AM

It depends on what is the other fluid as well, Boss. It's no good going for carbon steel if the other fluid is nitric acid, is it?

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energyconversion
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#2

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/24/2012 5:54 PM

All too vague to give an informed answer.
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Tornado
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#3

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/24/2012 9:02 PM

Is the other fluid the 30% brine mentioned in another thread?

What are the percentages of NH3, H2O, and CO2?

What is the purpose or process behind this unusual combination?

PVDF is probably not very high in thermal conductivity, thus doubtful for HX service.

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zanba
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#5
In reply to #3

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/25/2012 12:21 AM

Percentages of NH3, H2O, and CO2 is 41, 38, 21 respectively.

There isn't any other fluid in this part!

We want to use PVDF for the shell of exchanger, not the tubes. So, the low thermal conductivity is a useful property.

I know the reason of corrosion resistance of SS316 is formation of Cr2O3 and Cr2O3 layer formes in oxidizing media. But our media isn't oxidizing. Does Cr2O3 layer forme in this situation?

Thank you
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PWSlack
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#6
In reply to #5

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/25/2012 3:14 AM

<...There isn't any other fluid in this part!...>

How is an exchanger supposed to work with only one fluid?

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zanba
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#7
In reply to #6

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/25/2012 4:22 AM

Excuse me, I didn't understand his opinion.

Other fluid is a carbonated lisuid.
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PWSlack
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#8
In reply to #7

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/25/2012 4:37 AM

There is unlikely to be any corrosion issues with either material.

BTW: the measurement pH applies only to aqueous solutions and is meaningless in the context of gases.

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PWSlack
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#9
In reply to #7

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/25/2012 5:08 AM

Correction: it depends upon the carbonated liquid. If this is a misprint for "hydrocarbon liquid", then the above #8↑ stands. If the carbonated liquid has a low pH as a result of its being aqueous CO2 then more information about it is needed to resolve the materials selection issue.

A bunch of facts would go down a bundle on this thread.

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Jacob Klepatch
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#4

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/25/2012 12:03 AM

Any coating on steel needs preparation !! (especially PVDF)

As so the Stainless Steel will be cost beneficient -think about coating repairs later....

Suggested to do passivation on the stainless steel too.
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georgeh
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#10

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/25/2012 9:17 AM

Definitively SSS316L (better with "L" - Low Carbon, if the joints will be welded) over any further alternatives involving CS. Have special attention on the butt weldfng of the pipes (you don´t mention the pressure so I guess you have to joint them with a butt-welded procedure). They must made with a N2 purge to avoid the forming of chormiung carbides that eventually will form focus of corrosion. A little more expansive as an investment but dramatically better in a cost-benefit scheme.
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Whitephone
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#11
In reply to #10

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/26/2012 10:45 AM

What about DUPLEX (With N2 purge)?
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georgeh
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#12

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/26/2012 11:11 AM

What is DUPLEX?

This SS316L piping buttwelding process by TIG with Argon but the inert media inside the pipes (a couple of plugs in the ends and so on) with N2.

Regarding to Argon or Nitrogen for purging, this one is often used for purging stainless steel pipe and tubing systems. It is much less expensive than argon and it keeps the oxygen away from the root of the weld. Besides N2 is a diatomic molecule under "normal" conditions, and as this N2 molecule it is basically inert. But if someone want to use for the TIG process, N2 breaks down to single atoms in the welding arc and becomes very reactive with molten and hot steel, so Nitrogen cannot be used as an arc shielding gas. N2 can be used as a purge gas since it is not exposed to the welding arc.

Don´t think twice if you want a long life span!
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zanba
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#13
In reply to #12

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/26/2012 11:58 PM

Yes you'r right!

I'll think about it.

Thank you
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Anonymous Poster #1
#14
In reply to #13

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/27/2012 9:07 AM

Yes you'r right!

Yes, you're right!
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Whitephone
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#15
In reply to #12

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/27/2012 11:49 AM

Abstract

Duplex stainless steels have an extensive,

successful, track record in a

multitude of corrosive and erosive

environments up to 315°C (600°F),

while providing high immunity to

stress corrosion cracking (SCC).

Althoughduplex stainless steels are,

in many cases, superior in corrosion

resistance and strength compared to

304 and 316 austentic stainless

steels, many fabricators continue to

have difficulties creating welding

procedures that yield repeatable

weldments with optimum properties.

This paper offers practical welding

guidelines to new fabricators

who want to archieve high quality,

robust stainless steel weldments

supplementing API 938-C,. "Use of

Duplex Steels in Oil Refining

Industry". Discussion

includes the importance

of balancing ferrite

to austenite, reducing formation

of deleterious intermetallic and

nonmetallic phases, measuring ferrite

contents, and suggested welding

parameters.
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georgeh
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#16

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/27/2012 4:47 PM

OK, DUPLEX is better, more %Cr, they have a two-phase microstructure consisting of grains of ferritic and austenitic stainless steel in almost the same quantity. It makes a very high corrosion resistent. No doubt, is a superior choosing, but I think 316L for this aplication is enough. This is in the designer hands.
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Whitephone
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#17
In reply to #16

Re: Material Selection for the Gas (NH3+H2O+Co2)

06/28/2012 2:07 AM

Yes, and more expensive.
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Users who posted comments:

Anonymous Poster (1); Crabtree (1); energyconversion (1); georgeh (3); Jacob Klepatch (1); PWSlack (3); Tornado (1); Whitephone (3); zanba (3)

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