What's the Best Pipe Material for HCL 20%?

Can you confirm at what temperature?

Dear Guest

The operation/design condition as below:

Temp. Ope/Des. 30/55 Dec.C

Press. Ope/Des. 2/3.5 barg

You have a few options (without getting into really exotic alloys which aren't needed in this case), in decreasing order of preference (depending on size and cost)

1. Silicon cast iron: ASTM A861 (UNS F47003)
2. PVDF lined pipe
3. CPVC piping

You may even get by with PVC or PP piping as well. But, depending on the price of other options, these would be my last choice.

[And this, of course, depends on the piping code that you are building to]

Dear Guest

Thank you very much for your information

One more material that I forgot:

It would be ranked alongside PVDF lined pipe, and that is - FRP piping.

All of the Derakane resins are resistant at that concentration and temperature.

Corrosion Guide

For PP or PVDF, consider UV stablilisation.

You may also want to research HDPE. They are generally supplied with UV stabilisation.

Dear Sir,

Usually stainless steel of AISI -316 quality stainless steel material used as this steel is acid resitant . The life of these stainless steel pipes may be around six to 7 years .

PVC pipe can also be used of is used. but the life may be shorter.

The choice of material depends on economics and life expectency.

Warm regards,

D.N.Shenoy

I'm sory but guest is wrong. "Common" Stainleess steel (as 316) is not at all resistant to HCl, you will have leaks quite quickly! The best choice is with plastic materials. I would choose polypropylene. PVDF is even better but is quite expensive and not everywhere available. For both the technique is the same: welding (requires specific machines). I wouldn't use PVC as the temperature is above 50 ºC, but CPVC is a possible choice. You must regard UV exposure, generally PVC and CPVC are not UV stabilized. Some one raised the same question (UV) about PP. At least in Europe UV stabilized PP is common and quite cost efficient. For low pressures and temperatures the only advantage of metal versus plastic is that plastic is fragile, for example you can not stand over a low diameter plastic pipe. Depending on the instalation it may require mechanical protection in certain parts of it. Plastic lined metal pipes are quite expensive and are generally reserved for higher pressures.

I thought the use of stainless in HCl is a no-no, that the acid will attack the metal and then the land and material that is around the used-to-be-piping. I've heard that the time to failure can literally be hours.

Hi Betomachine

Agreed.

HCl causes stress cracking of stainless steel, where corrosion occurs preferentially along the lines of highest stress. It also tends to foster intergranular corrosion.

Sounds like this is essentially running at ambient temperature. In this case HDPE should be the cheapest alternative, provided derate to suit the highest ambient temp. Remember that the black of the HDPE will heat it well above ambient if it is in the sun and there is no flow through it to take away the solar heating. This can seriously derate the pressure capability.

With reference to NACE code Corrosion Data Survey-Metal Section, Sixth Edition, page 68, we find that Nickel Base alloys such as Ni-Mo has the following corrosion rates with Hydrochloric Acid (not aerated):

a. 50 micron/year (excellent rate) at about 20 ^oC and 20% concentration, and

b. 508 micron/year at 93 ^oC and up to 40% concentration.

I would add however that the corrosion mechanism that would dominate here is pitting corrosion and Chloride stress cracking, therefore general corrosion rates are really irrelevant and in fact are dangerously misleading in my opinion. If you ask me, the concept of "corrosion allowance" is a dangerous game to play because general corrosion in chemical process applications is actually pretty rare.

DO NOT use stainless steels in HCl service. The chloride attack on the stainless steels causes embrittlement of the metal and in a short period of time you will begin to see cracking of the steel and leaks. Welding the cracks only leads to more crack formation and you will chase these forever.

Typically I have used Teflon lined steel pipe for this service. Crane Resistoflex makes the best stuff in my opinion.

If you want to save money use Sch. 80 CPVC and line and run all the straight runs inside a galvanized pipe one size larger, this will help support the pipe as well as protect it from accidental damage from equipment and also protect it from UV. I also use the protective boots on all fittings and other places it is exposed. The boots will protect the fittings from UV and also prevent the acid from spraying on something in case some one accidentally hits it with equipment and breaks the CPVC. I also run my acid piping in an area of the pipe racks that will limit exposure to damage as well as as identify the pipe very well with the proper color and tagging. I have very good luck with this and I have several lines in service this way. I would not recommend this with higher concentrations of acid or in congested areas where allot of work could subject it to be accidentally struck by something. In these areas I would instead go with a nickle based alloy as Abdel Halim Galala has already said. In a perfect world all acid pipe would be run in some grade of Carpenter 20 or another Nickel based alloy. But I am sure most mills could not afford it as it is priced in todays markets. This is something that has to be looked at very carefully because if not done properly people can be hurt or even killed so please keep safety number one when deciding what material to use.

Some others have hit on this, but for the right material selection you need much more information than this:

What temperature, what contaminants might be in the acid (even at ppm levels this might be significant to some materials), how long does it have to last, how will the lines be cleaned during shutdown, what is the exterior service environment and is there access to repaint over time, how qualified are local contractors to install and maintain different types of materials ... there are many many options that may work for your application, but all have their pluses and minuses. I worked with HCl processes for 10 years and there is just not one right answer.

You are asking for a free answer to an ill defined question - not a good way to go for this nasty application - you ought to consult with (yes, even pay for) a qualified materials engineer who will know the right questions to ask and how those things will factor in.

scedule 40 carbon steel pipe with ubber lining can be used.As the reistance increases due to rubber lining the electricity bill will increase.

I'll add my 2 cents, although I am probably mostly re-iterating what has already been said. The "right" choice will, as others have posted, depend on much more than operating temp and pressure. Here are some general thoughts from my experience (10+ years in an HCl environment)

CPVC - Only used on small diameter drain line (low pressure/atmosphereic) applications indoors. UV issues as well as susceptability to physical damage and issues in cold ambeint conditions

FRP - good application if you have experienced pipe fitters. Pipe stress analysis and proper support is critical in long pipe-rack runs because of high thermal expansion of FRP pipe and potential to break/crack fittings - especially elbows. Improper bolt torque can crack flanges and/or create stress concentrators on bolted fittings. Epoxy joints are tough in the field - need heat source to properly cure in cold climates

Lined CS pipe - have tried mostly Teflon (PTFE, PFA) liners as well as Kynar (PVDF) and glass. I have no experience w/ polypro. Used a lot of teflon, but had much better long term performance with Kynar in low temp applications (<75 deg C). Teflon is a lot more permeable than Kynar and you will see steel corrosion around the weep holes after time (~5 years or so) with the Teflon lined pipe. No issues with the Kynar. Kynar is much more expensive, less readily available, and more difficult to flare. However, it is interchangeable to some extent with teflon lined so you could substitute a teflon lined piece in a pinch. Have moved away from glass lined as much as possible because of maintenance issues with mechanical damage and repair limitations.

Alloy 20, Hastelloy, Tantalum, Titanium - have tried them all in various parts of the plant. Bullet proof, but pricey. This is not that aggressive a service at this temperature and concentration so I wouldn't think these would be required. Unless vacuum conditions can be expected. The loose lined pipe doesn't react will to vacuum.

Hope this helps.

I like your comments about the CS/PTFE lined pipe. I see that many chemical companies use it because it is durable over thermoplastic but it does have the problem with permeation and corrosion. There is something new out called "Durcor" Piping System. It is an advanced "high strength" composite with PTFE lining. This eliminates the pipe corrosion and is an ANSI flanged system. Light weight and 100% corrosion resistant. Take a look and see www.durcor.com and the www.andronaco.com website.

Plastics. Consider PVC, PE, PP, PVDF.

Chemical Compatibility Database from Cole-Parmer (coleparmer.com)