Hello Steve,
You are not at all getting my point. As I said â I know the HF concentration & temperature for all classes. But I donât want to mention it.â Not because UOP will sue me, but I am concerned that any ignorant user may use it, without proper judgment. As I said âIt is dangerous play with HF. Hence I donât recommend any user to select the material based on my guideline.â
I said âPilot Plantsâ not scaled plants. You did not understand it properly. Yes UOP has data from their plants, which were constructed in late 60âs & 70âs.
Other than UOP data, I can mention some case regarding Carbon steel application with HF acid. A quote from material hand book â Steel on the other hand exhibits high corrosion rate in dilute HF solutions but may be used at room temperature in HF concentrations above 70 %.â If someone needs this corrosion graph (Metal vs. temperature vs. concentration) I could send scanned copy.
Also regarding corrosion in HF Alkylation plant I wish to quote the following: âThe most corrosive condition in HF Alkylation plants are normally encountered in the acid regeneration column & its preheater and the acid dehydrating column. As the Alkylation process proceeds the hydrofluoric acid gradually become more contaminated with high molecular weight organic material and water which remain dissolved in the acidâ
I wish to conclude this subject with the following highlights:
HF Alkylation plant is a dangerous plant. All precautions are to be taken in design.
Killed carbon steel is used as a basic material for the Alkylation plant except few cases.
If you are a piping engineer or process engineer, DO NOT try to select material for the plant, believe in what the process licensor recommends. (Even if you are confident)
Other guidelines I mentions are good & valid, you always find more such requirements while carrying out the plant design.
Also Hydrofluoric acid attacks Silica & Glass. So watch out for level gauge & other gauges dial material.
Finally to Steve, donât argue for the sake of arguing, Of course I know about velocity factor. It will be kept well in-control. But thatâs process engineer job. And by the way I said I did cut & paste from my experience. Not from Perryâs book or any other book. What I said was based on real experience.
Regards,
Umesh K.N.,
Sr. Piping & PDS engineer,
SK Engineering & Const. Ltd., Seoul, SouthKorea.
Steve McKenzie <mechproj@xtra.co.nz> wrote:Hi Umesh
nice answer, although I would research further if I had the time which I do not.
To get the preliminaries out of the way;
I do not know what an alkylation plant is, let alone have ever worked
on one. Nor do I know the scale factor between a pilot plant and a full
size one.
Sulphuric acid plants are very familiar to me.
So lets start from there as far as my background is concerned.
First, the original question did not state the HF concentration. your
"spec". stated steel for cold HF. I think we would agree that you would
not use steel for HF in applications where the concentration was
unknown, irrespective of service life.
Also "cut and paste" did you or didnât you? Of course you did.
Second, you mention the formation of a passive film which protects steel from further corrosive attack. With sulphuric acid you are no doubt aware that there are a range of critical velocities, dependent on diameter but typically around 0.6m/s, above which the protective film will be torn off and accelerated corrosion will commence. A line cannot be sized without knowing this velocity even if the temperature and concentration are suitable. Presumably the same applies with HF in steel. I can find no mention in your "spec" but am a fairly poor reader.
Third copper, I bow to your experience, but am surprised. Is it used on full sized plants?
Fourth, see first. I maintain specifying materials without specifying the operating envelope is a dangerous practice. If you would share a more little of your knowledge to provide a complete answer then my reservations would be removed. However if you consider, as you state, your information is proprietary information, and prefer not to divulge, then that is your perogative. But please state this up front or someone may make a nasty mistake, based on the information you have provided to help make a "better design".
Kind regards
Steve
-----Original Message-----
From: umesh k.n. [mailto:umesh_kn@yahoo.com]
Sent: Tuesday, October 19, 2004 9:21 PM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Hydrofluoric Acid Piping Guidelines
Hello There,
First, Steve: You wrote "It looks like a cut and paste job to me." Of course I was sharing the special instructions & design guidelines we applied in an Alkylation plant. What is wrong with that? I presume that you never involved in the design of any alkylation plants. You are writing mail as if i made up all this myself. As i told in my mail, the guidelines mentioned there, were actual facts from UOP licensor plants in Mexico, which were designed by us. Also in my mail i made it clear that "Most of the licensors specify these precautions. Apply them strictly". Because design practice varies from licensor to licensor. I was sharing UOP design practice. The important thing is the guidelines I mentioned in my mail gives anyone an idea about design complexity of the plant.
Secondly: Talking of corrosion, I wish to cut & paste from the following website. Hope you donât mind!!!!!!!!!!!. http://httd.njuct.edu.cn/MatWeb/mat-envs/feeee.htm
Performance of Steel in Various Corrosive, an Overview Introduction The applications for which the carbon and low-alloy steels were developed generally do not involve corrosion resistance as a primary consideration. In most situations, their serviceability depends on the fact that following the initial corrosive attack, protective films form that tend to reduce the corrosion rate to some acceptable level.
Corrosion Resistance
The corrosion resistance of steel depends on the formation of an oxide
surface film. In many environments this "passive film" formed on plain
carbon steel is not very stable. Hence, the resistance to corrosion is
somewhat limited.
Steel is routinely used for most organic chemicals and neutral or alkaline aqueous solutions at moderate temperatures. It is the classic material for storage of concentrated sulfuric acid and is frequently used for handling caustic soda up to 50% and 55C (130F).
If product purity specifications permit, steel is often used in services with corrosion rates up to 0.2 or 0.5 mm/year (10-20 mild/year) because of its low cost and ease of fabrication. In such case equipment wall thickness is increased to assure achievement of desired service life ("corrosion allowance").
Carbon steel should not be used in contact with dilute acids.
Thus it is not recommended with sulfuric acid below 90%. Between 90 and 98%, steel can be used up to the boiling point; between 80 and 90% it is useful at room temperature only. Above 102% (oleum) steel is good up to about 60C (140F).
So my point is that pure sulfuric acid or HF (above 90% concentration) in not corrosive than dilute one. BTW Hydrogen partial pressure, H2S content, Sulfur content also determine corrosion & hence metallurgy.
Thirdly: Copper for drip lines? Yes in case of Level gauge, level transmitter drains piping, 3/8" copper tubing is to be used at the end where pipe enters drain funnel. This is because areated hydrofloric acid is more corrosive than non areated HF acid.
Fourthly: Of course carbon steel is used for cold HF. The basic piping
metallurgy was killed carbon steel for the whole plant with the
limitation Ni+Cr+Cu<0.2%Wt. In the whole Alkylation plant only in acid
regenerator section Monel material was used where, temperature was 232
c. For all other sections mostly HF2 was applied. 3 mm corrosion
allowance was used in all HF cases. Also UOP has built several pilot
plants around the world & studied all the aspects of HF alkylation.
Hence you cannot struck down their historical knowledge by just using
Perry hand book.
You said âAre you sure this is a good guideline for a question where
temperatures and concentrations are not specified?â It is dangerous play
with HF. Hence I donât recommend any user to select the material based
on my guideline. I donât want to mention HF concentration & temperature
for all classes. It is UOP proprietary information. In my mail I
intentionally did not mentioned it. So donât ask more questions about
âHow Killed carbon steel is compatible?â. But it is true that killed
carbon steel was used as basic material. I DID NOT MADE UP A STORY. Also
âYes it is a good guideline for a piping engineer to start with.â
Finally my word is actual /historical experience is more valuable than text book knowledge.
Umesh K.N.,
Sr. Piping & PDS engineer,SK Engineering & Const. Ltd., Seoul, SouthKorea.
Steve McKenzie <mechproj@xtra.co.nz> wrote: Hi Paul
carbon steel for cold HF? How cold?
Copper for drip lines?
Monel for hot lines, how hot?
Are you sure this is a good guideline for a question where temperatures and concentrations are not specified?
I consider the response either irresponsible or with a knowledge far in excess of mine.
For example, cold hydrofluoric acid (Hf-2) is given as being compatible with steel. The general view of cold is unheated or at ambient. A medium ambient could be 30C. At a concentration of, say 40% HF, the corrosion rate of steel is in excess of 2mm per year. Check out the rest yourself.
It looks like a cut and paste job to me.
Certainly if temperatures, pressures and concentrations are not specified then such apparently authoritative data can be at best misleading and at worst dangerous. I hope Umesh will prove me wrong, as my concerns were based on commonsense (often unreliable) and an old copy of Perry nearby.
If carbon steel, as specified, is reasonably (say 0.1mm/year) resistant to HF at all concentrations and all temperatures which could be considered "cold" then I welcome being corrected.
Cheers
Steve
-----Original Message-----
From: Paul Bowers [mailto:pbowers@pipingdesign.com]
Sent: Saturday, October 16, 2004 6:59 PM
To: PipingDesign@yahoogroups.com
Subject: [PipingDesign] Hydrofluoric Acid Piping Guidelines
Umesh was so comprehensive in his response that I thought it should be reposted.
This is a good illustration of how complex certain piping installations can be. I've worked with liquid and high pressure hydrogen, but these requirements are pretty stringent.
Paul
umesh k.n. wrote:
> Hello Mr. Liu,
>
>
>>Can you share some experiences with me about Hydrofluoric acid piping
design >please? What should I watch out? Any special requirement besides
those in >common hydrocarbon piping design? The piping spec I'm using
now says, " Small >branch from bigger header has to be from horizontal"
why is that?
>
>
>
> Basic principles of HF piping design:
>
> q I was involved in the design 2 Alkylation plants in Mexico,
both of UOP licence. HF plant is a dangerous plant.
>
> q Piping layout shall be safe from all operation & maintenance
point of view.
>
> q Avoid complex piping layouts; avoid congested corridors (for
operator movement) and platforms.
>
> q If there are any valves to be regularly accessed, located
them at ground levels or in platforms.
>
> q While designing any piping configuration, remember that
operator shall always carry a portable breathing apparatus. This means
wider access areas & platform areas.
>
> q All vents & drains in HF class piping shall be either routed
to flare or u/g drainage system.
>
> q Design the escape ladders, smartly..so that upon anticipating
danger, operating personnel should able to get out of the plant easily &
quickly.
>
> Special notes related to piping design:
>
> q Copper tube piping shall be provided at the end of all drain
lines leading to Acid Funnel.
>
> q 2â above lines shall have ¾â vent at all pockets.
>
> q HF acid pumps have Alkylate flush supply & return, Isobutene
flush, lines.
>
> q Each acid pump drain shall be flared before pump is removed
for maintenance.
>
> q Each pump seal pot vent line shall be separately routed to
Flare header.
>
> q Acid unloading line requires special support arrangement (No
pocket design)
>
> q Catalyst loading / Unloading type reactors shall require
special attention during design stage.
>
> q Portable exhauster connection shall be tangential tap to
pipe.
>
> q Each Control valve shall have drain line connected to flare.
>
> q When CV is to be taken out for maintenance, close the
isolation valves & Flare the drain first.
>
> q There will be separate emergency Air header in rack to feed
emergency booths.
>
> q Drain valve is necessary between high Pr. double b/v for
Bleeding
>
> q Breathing air stations shall be located throughout the plant.
>
> q Portable breathing air apparatus shall also located in high
risk areas.
>
> q Level gauge, level transmitters vents shall be routed to
flare.
>
> q Level gauge, level transmitters drains shall be routed to u/g
drain as well as to flare.
>
> Draining procedure in any HF class piping:
>
> q While you are in HF area safety clothing with mask & a portable
breathing air apparatus is a must.
>
> q Generally all the drains will have an u/g drainage connection
and a flare connection.
>
> q First open the drain valve to u/g acid drainage system.
>
> q Secondly, open the valve in the flare connected line to remove
HF gas.
>
> q Thirdly use a portable exhauster to purge any left over HF gas
to flare.
>
> HF1- class Piping: (Hot Hydrofluoric acid, Monel class, 300# R.F.) >
> q Bosses on valve shall not be drilled unless indicated in
P&ID.
>
> q If shown in P&ID ¾" Sch 80 pipe nipple shall be shop socket
welded to main valve.
>
> q All ¾ " connection to larger lines shall be reinforced by
gussets.
>
> q No unions permitted.
>
> q Install bleeder connection in the cavity between two seating
surfaces of gate valve.
>
> q All valve and swing check valve âGâ point drain size shall be
¾ â size.
>
> q Ring joint with soft iron ring (or monel ring) is acceptable
alternate to R.F. flanges.
>
> q Spiral wound gasket shall have flange surface finish of
125-ra minimum to 250 max.
>
> q Each casting shall meet the hydrostatic test of ASTM A703
requirements.
>
> q All welded piping components shall be post weld heat-treated.
>
> Hf-2 class Piping: (Cold Hydrofluoric acid, Carbon steel, 300# R.F.)
>
> q Minimum line size is 1" except instrumentation connection.
>
> q All 1" drain connection shall be tangential to process
piping.
>
> q All bleeders shall be located in horizontal plane.
>
> q Bleeders tapping could be ¾" size.
>
> q All reducers shall be eccentric with flat side down.
>
> q Temperature limit for plug valve 177 c.
>
> HF-1 and 2:
>
> q All valves shall have grease injector threads.
>
> q All pipe girth weld shall be full radiography. (ASME b 31.3
Para 344.5)
>
> HF-4 (Traced HF acid, Carbon steel, 150#RF) & HF-5 (Traced HF acid,
Carbon steel, 300# R.F.)
>
> q All pipe girth weld shall be subjected to 10% random
radiography. (ASME b 31.3 Para 344.5)
>
> Hf-2, 4, and 5:
>
> q All CS pipe shall have the following chem. Composition: Ni +
Cr + Cu < 0.2 wt %
>
> q All welds except socket welds shall have a maximum weld
hardness of 200 Brinnel.
>
> q If weld hardness exceeds 200 BHN one hour at a minimum temp.
594 c
>
> q All socket welds shall be liquid Penetrant inspection. (ASME
b 31.3 Para 344.4)
>
> Hf-1, 2, 4 and 5:
>
> q No SS gasket or valves.
>
> CAUTION!
>
> q HF Acid is extremely dangerous. Follow all industry, local
and internal safety procedures when dealing with any valve or valve part
that is intended for HF Acid service.
>
> q Before performing any work and/or disassembling any valve,
ensure that all pressure has been removed from the line and from any
cavities within the valve.
>
> q Prior to commencing with any internal work on HF Acid service
valves, ensure that the entire valve has been properly neutralized. >
> q Hydrofluoric Acid is a highly corrosive acid, which can
severely burn skin and eyes. The vapors alone from HF acid can cause
severe burns to these tissues. It is therefore of extreme importance
that workers familiarize themselves with the specialized Hydrofluoric
Acid Safety Guidelines before working with equipment containing, or
having contained, hydrofluoric acid.
>
> q HF is a severe skin, eye, and respiratory irritant, which is
unusual in that pain may not occur initially upon contact with the acid.
Therefore, HF can penetrate deep into tissue without warning, causing delayed pulmonary edema or deep tissue burns requiring immediate medical
attention. HF, which penetrates into tissues, may cause slow tissue
death, resulting in very undesirable effects, such as the loss of a
finger, which came into contact with the acid!
>
> Most of the licencors specify these precautions. Apply them strictly.
Give special attentiion to P&ID notes..
>
> Hope this will guide you towards better design,
>
>
>
> Regards,
>
>
> Umesh K.N.,
> Sr. Piping & PDS engineer,
> SK Engineering & Const. Ltd., Seoul, SouthKorea.
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[Non-text portions of this message have been removed] Received on Wed Oct 20 00:56:00 2004
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