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Carbon Steel for Instrument Air Pipe

Carbon Steel for Instrument Air Pipe

Carbon Steel for Instrument Air Pipe

(OP)
Hi,

Is it common to have API 5L B (without galvanised) for the instrument piping material?

Based on my previous experience it should be pre-galvanised, however on my current project it is specified as API 5L B without galvanised?

Any advise

Thanks

norzul

RE: Carbon Steel for Instrument Air Pipe

(OP)
What are the advantages & disadvantages of having galvanised?

RE: Carbon Steel for Instrument Air Pipe

If you have wet instrument air then the carbon steel will corrode and the corrosion products (rust) may end up damaging or blocking instruments.  Galvanising can serve to prevent this process (for a certain period of time).

Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/

RE: Carbon Steel for Instrument Air Pipe

(OP)
I think our instrument/plant air is dry, since we have air dryer units downstream of the air compressors....its dewpoint is -40oC

So its OK then...

Thanks

OK

RE: Carbon Steel for Instrument Air Pipe

Many plants use only stainless for all air lines.  Dry air is never really dry, and dryers fail from time to time.
In the long term a lot of money can be saved by having a clean air system.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm

RE: Carbon Steel for Instrument Air Pipe

EdStainless- you are absolutely right. We are now fighting this exact situation. Sometimes in the summer the dryer isn't even turned on... (ARRGGG!) If I had the choice I would use stainless and heavy duty/high flow filtering right after the dryers. Then at each critical outlet I would dry and clean as described in this thread:

thread1036-137393

And notice rmw's statement at the bottom.

RE: Carbon Steel for Instrument Air Pipe

(OP)
TQ for the advise/lessons learned....welll...it's a bit late for our project, already specified CS & in the final stage of procurement, construction in 2-3 months time.

Not much choice but to proceed with CS. In any project, besides quality, there are 2 other factors that need to be considered i.e. schedule & cost

Hope for the best....

RE: Carbon Steel for Instrument Air Pipe

It's usually cheaper to do it right the first time...... winky smile

RE: Carbon Steel for Instrument Air Pipe

If the instrument air is wet, you may have other problems besides corrosion. Your instruments may also freeze.

Most places that I know of use carbon steel without galvanising. I don't know of any sites with all stainless steel instrument air piping system. Stainless steel pipes would cost a lot more. The welding would also be different I would think - although I am not familiar with stainless steel welding.

EdStainless, a quick question to you. What is the instrument air receiver/volume tank made of? If it is carbon steel, does that mean it has a liner?

RE: Carbon Steel for Instrument Air Pipe

(OP)
After further investigation, I believe this is a matter of choice. We have been operating 2 refineries (100,000 BPSD each, sweet & sour) which had been in operation for more than 10 years already. Use CS for both, plant & instrument air. However, we do have filters & dryers downstream of air compressors. So far haven't heard any major problems on the filters, dryers & the entire air system except on one of the air compressor.

Our company standard also doesn't really emphasize on using galvanize or SS. My previous project, as I previously mentioned, specifying galvanized CS...I can't recall why...

RE: Carbon Steel for Instrument Air Pipe

norzul,

A quick question to you on the material of your instrument air receiver/volume tank. Is it also CS?

RE: Carbon Steel for Instrument Air Pipe

(OP)
Most likely it is CS, but i'll double check tomorrow, already 12:43am time...going to sleep...

RE: Carbon Steel for Instrument Air Pipe

(OP)
Can't find the eqpt datasheet, but from the PFD & P&ID, looks like CS

RE: Carbon Steel for Instrument Air Pipe

lined CS for tanks and such.
I hate to through a plug in here, esp since it isn't my product.  I have seen a number of plants run air line using Victaulic Press-Fit http://www.victaulic.com/docs/lit/pb-500.pdf

The last SS tube mill that I worked in ran all SS air (and all gass) lines with long runs of tubing and orbital welded joints.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm

RE: Carbon Steel for Instrument Air Pipe

(OP)
TQ EdStainless....new knowledge for me

RE: Carbon Steel for Instrument Air Pipe

Thanks for checking norzul.

Thanks edstainless. Is it possible for you to indicate in what part of the world, and what specific industry, you have seen SS instr. air? If you can't, no worries.

It is just such a foreing concept (SS instr. air lines) to me, and my industry here.  

I will now definitely keep my eyes open for a SS instr. air system.

RE: Carbon Steel for Instrument Air Pipe

The first place that I saw it was in air lines for paint spray booths, which must be kept very clean.
Since then I have seen it in drug plants, breweries, and even is some manufacturing plants that have a lot of air driven equipment.  They say that it significantly reduces wear and failure of air cylinders and controls.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm

RE: Carbon Steel for Instrument Air Pipe

EdStainless,

Thanks for the context info. I learned something new today. You get a star.

These industries you mention are completely foreign (I typed it correctly this time) to me.

I can see industries such as breweries, drugs, painting, etc. being held to a different standard wrt cleanliness - and therefore SS instr. air systems.

In oil and gas, I guess you can say we are not so fussy. In fact, we don't even always use air all the time. We often also use propane (from bullets) and process gas (the gas we are shipping is also used for instr activation) when air is not available. Where gas of any sort is unavailable, we use self contained hydraulic systems.

Thanks.

RE: Carbon Steel for Instrument Air Pipe

The term 'clean dry air' is an oxymoron.  (But I repeat myself.)

thread378-123404
thread378-122965

rmw

RE: Carbon Steel for Instrument Air Pipe

(OP)
welcome rmw....I learn new word now..."oxymoron"

RE: Carbon Steel for Instrument Air Pipe

rmw,

Would you classify "bottled" air as "clean dry air" - the ones used in breathing apparatuses?

RE: Carbon Steel for Instrument Air Pipe

I've been associated with the petrochemical, chemical and metallurgical industries for almost 40 years.  Stainless, copper and in some cases even poly is used for instrument air since it can be field fitted more easily than cs and since it has thinner walls, but other than cs being a dirty steel as compared to the other materials there is no reason not to use cs.  If you look at the price of all I'm sure you will see why they selected cs.
In any case I have never seen inst air used that is not dried and of course filtered.  What are people thinking if they are not using dried air for sensative instruments and electronic operators.
Most instrument suppliers will also specify the type of connections and types of gases acceptable for instrument operation.  If they haven't then ask them to do so such as to comply with their guarantees.
tcinc002@aol.com

RE: Carbon Steel for Instrument Air Pipe

For most valves that I spec, I also include a filter and regulator with the pneumatic actuator that I purchase.

RE: Carbon Steel for Instrument Air Pipe

Yes I agree.  The filter will take out any debris and the regulator is required for any Pneumatic actuator, but the filter will not take out any liquids.
As an afterthought, the design that we mostly employ for the instrumentation air is cs from the air reservoir and/or compressor to the vicinity of the instrument then SS or copper, depending on the duty, to the instrument, with of course vibration resistent mounts.  We also like to use swagalock fittings (quick disconnects)  and sometimes flex couplings or fittings directly on the instrument to reduce any potential leaks from vibration.
The selection of copper vs. SS depends on the duty.  Mostly in petrochemical we stick with SS due to the atmospheric corrosion potential and higher pressure requirements of safety items, valve actuators.  We also recommend strict compliance to maintenance for the filters, dryers, and periodic soap tests on connections.  Dryers are also checked for dew point on a regular basis if not on-line moisture analyser.
tcinc002@aol.com

RE: Carbon Steel for Instrument Air Pipe

tc002,

Yes, tubing from the instrument air header/piping system to the instrument is usually SS. You won't find much CS tubing.

However, the original thread was about instrument air piping, not the tubing to the instrument.

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