Piping material for H2SO4 at negative temperatures 4

[PedroAssis]

Dear all,

I'm looking for a suitable pipe material for this application in a waste treatment plant but I couldn't find a solution so far.

Fluid: H2SO4 96%
Ambient temperature: -20 to 30 ºC
Fluid temperature: -20 to 30 ºC
Operating pressure: up to 3 barg

Do you know of a pipe material that has the required chemical resistance and is suitable for there operating temperatures?

Thank you very much
Pedro

 

[EdStainless]

Will it always and only be 96% acid?
You do know that the freezing point is -14C.
Why not just use 304L or 316L?
If you really want something better look at 825, AL-6XN, or 904L.

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P.E. Metallurgy, consulting work welcomed

 

[mk3223]

Typical material for sulfuric acid reference:

http://www.inyoprocess.com/concentr...t=The best piping material is,of about 350°F.

 

[EdStainless]

If you want an authoritative source.

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P.E. Metallurgy, consulting work welcomed

 

[Ramzee09]

Hello pedro,

in my opinion you should have a pipe lining for that application.
I have many experiences of waste water or utilities application with normal environment instead of cold plant as you are. PTFE Lining on carbon steel (coated) would be economize for you, the ptfe will protect the pipe while transferring the H2SO4 media from the inside. or if you are having a very bad environment attack environment from the outside you can have ss 304 with PTFE lined pipe.

regards,
Pram

 

[shvet]

Note that during cold weather concentration of H2SO4 shall be higher 96%.

https://files.engineering.com/getfi...e=Willoughby_Plastic_Piping_Handbook_2002.png

Section 2: Specific Materials
2.1 Carbon Steel
2.1.1 Carbon steel is satisfactorily resistant to concentrated sulfuric acid at ambient temperatures under static or low-velocity conditions (less than 0.9 m/s [3 ft/s]); ...
2.2 Cast Iron
2.2.1 Gray cast iron and ductile cast iron are both more resistant to corrosion by concentrated sulfuric acid than is carbon steel. ...
2.2.2 Gray cast iron has lost favor in recent years because of its brittle nature. Catastrophic ruptures have occurred in piping as well as pressure vessels. Ductile cast iron has been used successfully for thickwall piping and is recommended over gray iron. Gaskets used with ductile iron piping should match the pipe bore to minimize acid turbulence.
2.2.3 High-silicon cast irons (UNS(2) F47003 with 14.5% Si) are resistant but are seldom used for simple handling and storage because of their inherent brittleness.
2.3 Stainless Steel
2.3.1 The conventional austenitic stainless steels of the Cr-Ni and Cr-Ni-Mo type are generally resistant to ambient-temperature, concentrated acid because they have a naturally formed passive film. ...
2.3.2 The molybdenum-bearing grades (e.g., UNS S31600/S31603 or UNS J92900/J92800) are recommended for improved resistance to velocity enhanced corrosion or impingement in valves in the entire concentration range.
2.3.3 Duplex stainless steels have found successful applications in ambient-temperature concentrated acid, in the form of valves and pumps cast from copperbearing UNS J93370 and fabricated components from wrought UNS S31803 material. ...
...
2.3.5 Four to six percent silicon-containing stainless steels (UNS S30600, UNS S30601, and UNS S32615) perform very well in ambient-temperature, concentrated sulfuric acid, but are more typically used for hightemperature, turbulent applications found in sulfuric acid production plants.
2.4 High-Nickel Stainless Steels and Nickel Alloys
2.4.1 Nickel chromium-iron-copper-molybdenum alloys or their cast versions (see Appendix A) perform better and are more resistant to concentrated acid than 18Cr-10Ni-Mo stainless steel under the increased velocity conditions found in pumps and valves.
2.4.2 Alloys of the nickel-chromium-molybdenum type, such as UNS N10276, UNS N06625, UNS N06022, UNS N06455, UNS N06985, UNS N06059, UNS N06200, and UNS N06686 or their cast versions, offer excellent resistance to concentrated acid and are especially useful for applications in which high temperatures and significant acid strength variations are possible.
2.5 Other Alloys and Metals
2.5.1 Nonferrous metals such as zinc, tin, copper, and nickel are not resistant to sulfuric acid and therefore have no useful applications in its handling and storage. Aluminum grades UNS A91100, UNS A93003, and
UNS A93004 have been used successfully for handling sulfuric acid in the concentration range of 98 to 100%, but are not generally recommended.
2.5.2 Chemical lead is resistant to sulfuric acid but the protective sulfate film is increasingly solubilized above about 95% concentration and 25°C (77°F). ...
2.5.3 Of the reactive metals, titanium and zirconium must not be exposed to concentrated acid. Tantalum is resistant to concentrations up to 97% acid and thus finds some application, especially as an electroplated coating for orifice plates.
2.5.4 Of the noble metals, gold and platinum are resistant to sulfuric acid but of very limited applicability. Gold is used to condense and cool reagent-grade acid. Silver is not resistant to sulfuric acid.
2.6 Nonmetallic Materials
2.6.1 Organic
...
2.6.1.1 The fluorinated plastics listed below are resistant to concentrated acid at the temperatures covered by this standard:
• polytetrafluoroethylene (PTFE);
• perfluoroalkoxy (PFA);
• ethylene chlorotrifluoroethylene (ECTFE);
• fluorinated ethylene propylene (FEP); and
• ethylene trifluoroethylene (ETFE).
2.6.1.2 Polyethylene (PE) and polypropylene (PP) are subject to environmental cracking. ... Polyvinylchloride (PVC) and polyvinylidene chloride (PVDC) have been used successfully as piping materials for concentrated sulfuric acid, but should not be used for acid strengths greater than 96%. ... Polyvinylidene fluoride (PVDF) is resistant to sulfuric acid up to 98% concentration.
2.6.1.3 Chlorosulfonated polyethylene has been successfully used for hoses handling up to 93% acid. ...
2.6.1.4 High-temperature baked phenolic coatings are routinely used in storage tanks and rail tank cars containing 90 to 98% sulfuric acid in which iron contamination must be minimized and/or corrosion protection is required. At acid concentrations greater than 98%, some types of baked phenolic coatings slowly carbonize. ... High-temperature baked phenolic coatings have provided many years of satisfactory service in concentrated sulfuric acid when properly applied, cured, monitored, and maintained.
2.6.1.5 Polyester, vinyl ester, nylon, and epoxybased materials are attacked by concentrated sulfuric acid.
2.6.2 Inorganic
2.6.2.1 Carbon and phenolic-impregnated impervious graphite are resistant to sulfuric acid up to 96% concentration.
2.6.2.2 Glass, glass-lined steel, and acid-brick ceramics all have satisfactory resistance to all concentrations of sulfuric acid.
Section 3: Specific Equipment
...
3.3 Piping
3.3.1 Materials selection for concentrated sulfuric acid piping depends on a number of factors including size, velocity, pumping schedule, contaminants, desired life, and potential dilution.
3.3.2 Carbon steel piping may be used at ambient temperature and low flow velocity (i.e., maximum 0.9 m/s [3 ft/s]). Flow velocities of up to 1.5 m/s (4.9 ft/s) may be allowed if the pumping schedule is brief (e.g., a few hours per day). Good-quality welds are essential, and multipass welds should be used. ...
3.3.3 Carbon steel piping in intermittent service can experience accelerated corrosion because of hydrogen grooving or dilute acid attack. Consideration should be given to drainage and blowing carbon steel lines free of acid using dry air or inert gas.(9) Crevices caused by threaded or socket-welded piping can make the draining or blowing out of acid difficult.
3.3.4 Ductile cast iron pipe has an increased tolerance for higher velocities when compared with steel. Ductile cast iron is preferred to gray cast iron, because it offers better ductility in addition to comparable corrosion and erosion resistance in the acid strengths covered by this standard (see Paragraph 2.2).
...
3.3.7 UNS N08020 has been successfully used for small-diameter piping, especially when flow velocities exceed 1.8 m/s (5.9 ft/s).
3.3.8 Plastic-lined piping with PVDF or PTFE liner has also been used successfully. However, PVDF shall not be used for acid concentrations above 98%. Experience with PP-lined concentrated acid piping has been mixed ...
3.3.9 When solar heating is extreme or when heat tracing is required, UNS S31603, high-nickel stainless steels, or nickel alloys are favored (see also Paragraph 3.8.1).
3.3.10 Solid thermoplastic piping should only be used in concentrated sulfuric acid service after a detailed engineering review. (Also see Paragraph 2.6.1)
3.4 Valves
3.4.1 For simple shut-off valves, molybdenum-bearing stainless steel should be used. The industry standard is UNS J92900; UNS J92800 is an acceptable alternative. Copper-bearing UNS J93370 valves are sometimes available at little additional cost and offer greater resistance to dilute acid if it is formed (see footnote 9). UNS J95150 and nonmetallic-lined valves have also been successfully used for this type of service.
3.4.2 For throttling valves with higher velocities and turbulence, UNS J95150 has been used successfully. This alloy is also appropriate for use in stock-tank plug valves employed to protect against inadvertent localized dilution effects. PTFE-lined valves have alsobeen successfully used in this service.
3.4.3 PTFE-based packings and PTFE (filled or unfilled) and fluoroelastomer nonmetallic parts are acceptable for service in concentrated sulfuric acid valving.
3.4.4 A proprietary cast Ni-Cr-Co-Mo-Fe-Cu-Si alloy has been used successfully for valve seats and trim in concentrated acid service at ambient and higher temperatures. This alloy is also used for piping orifice plates.
3.6 Gaskets
3.6.1 Compressed sheet asbestos gaskets and asbestos-filled, spiral-wound gaskets have been used successfully for decades. However, their use has been curtailed because of personnel exposure concerns. Suitable alternatives to asbestos are listed below and should be utilized when required:
• PTFE-, silica-, or aluminum silicate-filled PTFE
• Stainless-steel spiral-wound PTFE
Fluoroelastomers are also appropriate.
3.6.2 Envelope gaskets are satisfactory if the elastomeric or other compressible material within is effectively shielded by a fluorinated plastic envelope.

 

[hacksaw]

What is the expected acid flow rate required for your treatment process?

 

[pierreick]

Hi,
Consider this booklet to support your work.
Pierre

 

[PedroAssis]

Dear all

Thank you very much for your great help.

The client has an additional requirement. It must be a pipe in pipe or hose in pipe solution, with slope to containment boxes with level switches for leak detection.

Considering your feedback I think stainless steel 316L might be a good option because of the cold temperatures. For the outside pipe, maybe we could use a PEHD pipe or hose. PEHD is not super resistant to H2SO4, but it is just for containment.

More feedback is welcome. I will keep investigating.

Thank you very much
Pedro

 

[shvet]

@Pedro
Curious to know logic behind this. You use expensive SS in controlled indoor conditions while in your case it has no advantages and vice versa use cheap plastic having disadvantages in uncontrolled outdoor conditions. How it works?

1/ How are you planning to control plastic cracking? Why do you believe this pipe will not rupture suddenly and kill a 1-2 dozens of persons? Note that 3 barg equals to 15 meters of upward acid jet and more backward.

2/ Note that SS has the same corrosion rate and mechanism as CS. What is the reason to use SS?

3/ How personnel is going to control, inspect and test such containmed piping?

I had worked at an H2SO4 facility for 9 years as an operating team and more as a designer. Your design is odd and random. Do you have a proper background?

https://www.eng-tips.com/viewthread.cfm?qid=512266

Note that H2SO4 is the oldest and most studied product in chemical industry. When one is speaking "chemical industry" it mostly means processes involving H2SO4, chlorine, aniline and such. Why do you believe such product category requires a special supercostly handling like double-wall piping equipped with level switch?

update

4/ Check design min temperature of HDPE compound - as far as I remember piping pressurized components made of polyolefins are prohibited at temperatures below 0°C.

POLYETHYLENE PIPE
...
Durability
... Some strong oxidizing agents, such as sulphric or nitric acids, can cause problems for PE piping. ... Extended exposure to strong oxidizing agents can lead to crack formation or crazing on the pipe surface. ...

 

[dik]

It's interesting that the liquidus/solidus curve presented by shvet has so many values depending on the concentration. Great discussion...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[shvet]

@dik
Because freezing acid behaves not as a mix of 2 substance (e.g. H2SO4 + H2O) but as a mix of plenty of separate substances (e.g. H2SO4 + H2O, H2SO4*H2O + H2O, H2SO4*2H2O + H2O and so on)
and vice versa for boiling

 

[EdStainless]

And if you want more confusion about temperatures and phases these charts end at 100% rather than extending into the oleum range.
The biggest reason to use SS is because you are either trying to limit the Fe in the acid or you have velocity related concerns.
I agree, using a lesser material for the outer containment is a foolish direction. I could see using plain steel for the outer piping.
You can easily buy centering spiders for supporting the inner pipe.
I would look into buying the pipe sections premade.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

Thanks, Gentlemen...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik