Demineralized Water Piping 1

[AEF]

Can someone please help solve a raging debate regarding the corrosivity of demin water and why demin systems and tankage are made of 304 stainless? Is demin water any more corrosive than fresh, aerated, potable water? Is the piping made of stainless to prevent iron pick up prior to it entering the deaerator, or because it would chew through carbon steel quickly? None of the water treatmet manuals,like Betz, really delve into this. Is this a chicken or egg type debate? Help!!

 

[DeltaCascade]

Betz Handbook does address this, although indirectly.

Calculate the LSI (langelier stability index) of demin water. You will see that the scaling tendancy is non-existant (low LSI, no surprise there), and, hence, the corrosive tendancy is very high (low, negative actually, LSI value).

Demin water loves to dissolve stuff. It is quite aggresive. Add dissolved oxygen and "say bye-bye to" carbon steel.

Iron pick-up is a practical problem in economizers, etc., due to large surface areas, but is controllable (obviously).

 

[stanier]

Try the Nalco handbook or the Nalco books on corrosion. There are two. One for power generation and the other for general industry. If you specify lots of their chemnicals the representative will give you copies.

Why not use ABS piping for demin water. See

http://www.eurapipe.com.au

for details. Its more ecomomical than ss and will not contaminate your systems. It is used in the microelectronics industry for ultra pure water.

 

[YOSAFAT]

I want to support you about demin water. The Characeristic of demin water is corrosive, the langilier Index is negatif so it mean that the demin water corrosive tendencies. The demin water may be used for boiler feed water, is this true?
Materials for construction demin water tankmust be stainless steel SS 304, becouse SS 304 is very resistance with corrosive.

 

[DeltaCascade]

For boiler feed water quality, ASME guidelines are recommended.

Demin water is often used for boiler MAKE-Up water. It is blended with condensate returns (to make up for losses through boiler blowdown, etc), then sent to a deaerator. Feed of oxygen scavenger and amines downstream of the deaerator "scrubber" section, that is, to the dearator storage section, is typically done to adjust water pH there, and to add amines for condensate pH/corrosion control (amines avaporate in boiler and "follow" steam to condensate lines). So, boiler feed water is DOWNSTREAM of the deaerator. Make-up water (with dissolved oxygen stil in it) and condensate returns are upstream of the deaerator.

Hope that helps.

 

Most of our systems use deionize/demin water. We passivate all brass and copper sections prior to use with demin water as this greatly reduces corrosion...

May be useful to someone...

 

[WTP03]

I have a question regarding the bench pH testing of boiler water. Should the sample be stirred(aggitated) while it is being tested or will this result in a lower pH reading due to more dissolved gasses being introduced to the sample. ?

WTP03

 

[plainwater]

AEF, why dont you try using lined tanks and pipes in place of SS304 for DM water. that may be more cost effective.

 

[AEF]

Thanks for all the replies. Your info has been very helpful. I would like to re-state one of the questions though; Is demin water piping made of stainless (or other corrosion resistant material) because of the corrosiveness of the water or for process reasons? Is there an engineering or construction standard, guideline or code that details (and explains why) recommended materials of construction?

Looking forward to your responses!

 

[smile1]

Demin piping is stainless steel because of the corrosiveness of demin water. Pressure rating is another requirement that will determine system design.

 

[Nicksun]

AEF,for your first question,both of the reasons are right,and i weigh them equally. Also,LSI negative,corrosion resistant material is required; and high qulity of POU also need the "stainless"-like material.

for the second question,i THINK there is no such specific and authorized standard.right?

we are waiting for more answers.

 

[bimr]

SS piping is used because of the corrosiveness of the demineralized water. However, if you remove the oxygen from the demin. water, the corrosiveness of the water will be reduced.

Carbon steel is used successfully to construct high pressure boilers where the oxygen level is very low and the boiler water is basically demin water.

SS is used basically for corrosion prevention, and not to prevent contamination of the water. In other process applications such as biotechnology where demin. water is used, there may be issues with contamination of water.

I am not aware of any guidelines that cover all applications.

 

[plainwater]

DM Water pipeline is made of stainless steel because of two reasons; corrosivity and temperature of water. You may get more help from Powell's book.

 

[stanier]

For ultrapure water inthe electronics industry ABS is used quite extensively in SE Asis. Not the ABS produced in the USA thatnhas had its problems but that made in Australia, Malaysia and Indonesia to Australian Standards AS 3518.

I withstands the high corrosivity of demin water and more importantly does not contaminate the water. Water used for flush cathode ray tubes, LCD screens etc cannot toelrate on e speck of iron as this fluoresces when the elctrons are fired at the screen.

By the way it is cost effective against ss. You dont need TIG welders, X ray etc.

You can share knowledge but you cant share wisdom. Using knowledge wisely separates engineers from the enthusiastic amateurs that burden our society

 

[AEF]

Again, thanks for all the responses. Stanier (Mechanical), you mentioned an Australian Standard for ABS, AS 3518, noting that it's used in preference to US Standards for ultra pure water service. Which US standards? ASTM? We operate a isoocatane petro-chemical refinery in Alberta, Canada, and are normally limited to using CSA, ASTM/ASME/ANSI standards for our metallic and non-metallic piping systems. I'd like to compare the ABS piping spec to see if it's applicable for our use but I need to know what to compare it to! I'd like to start using more non-metallic piping in our facility for water and neutralization service, where warranted, and am always looking for a better material.

 

[stanier]

Hi AEF,

ANSI B31.3 lists the properties of three grades of ABS material. I believe the manufacturer of the resin may be Uniroyal. I dont know the relevant ASME standard but it may appear in B31.3.

The reason I mention the difference in AS 3518 materials and the US materials is the high profile case of failures of ABS in the pluming industry in the US. I think this may have been settled now.

The pipe manufactured here has a different blend of acrylonitrile butadiene stryrene and is master batched differently. This results in a pipe material with different properties.

It is manufactured up to DN800 and 15 bar (at 20C)rating.

Its main applications is in mineral processing, slurries, water and waste water, effluent treatment, building services etc. It offers good corrosion resistance internally and externally.

Its low modulus mitigates waterhammer pressure transients as the celerity is reduced.

I have been designing and installing this material in applications in SE Asia for over twenty five years.

It is also available in a ready insulated system ideal for reticulating chilled water to buildings and plant.

Chek it out at the manufacturers website.

http://www.eurapipe.com.au/cd/Eurapipe/default.htm

I do not have any commercial interest in this company. My interest stems from a good product that out performs legacy materials in specific applications.

Where carbon steel pipe needs repainting every five years and replacing in ten ABS keeps going. A simple NPV shows the net worth of the ABS installation.

Esso use in Malaysian offshore applications. You cant get a better recommendation that that.

You can share knowledge but you cant share wisdom. Using knowledge wisely separates engineers from the enthusiastic amateurs that burden our society

 

[seanmc]

There is alot of discussion on ABS piping here. Why would I choose ABS piping when according to my piping handbook PVC is stronger, more chemically resistant and more economical?

 

[bkmuduli]

What is the ASME standard that recommends a particular Boiler Feed Water Quality??

 

[AEF]

The ASME standards that were refered to are only for materials for piping fabrication (ASME Section 2 Parts A-D). I'm not aware of any ASME standard that references boiler feed water quality. ASME Sections 6 and 7 are rules and guidelines for the care and operation of heating and power boilers, but I'm not to familiar with thier contents.