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Buttterfly valves specs .

Buttterfly valves specs .

Buttterfly valves specs .

Hi , we are working with one client on Butterfly fly valves specification for TSE ( Treated sewage effluent ) and Water treatment plant the body is ductile iron but the problem is the disc material is stainless steel which is dose not make seance for us !!

kindly share your opinion about it from engineering point if view


RE: Buttterfly valves specs .

Hi Hyari,

TSE and water treatment means that the "water" is sour. thus should comply with NACE MR-0103.
and both material Ductile iron and (ferritic/martensitic/austenitic) Stainless steel in general conform that requirement.
Of course there are some remarks over hardness, chemical composition and heat treatment procedure should be more looked into.
Ductile iron body, I assume the piping is either Carbon Steel and or Ductile iron?
And when you mention trim, is the Seat also SS or is it elastomeric?


All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

RE: Buttterfly valves specs .

Hi, hyari!

You have not given the size of the valve here, and I assume the pressure is in not of the higher classes. From producers side the materials could also vary based on size and cost.

In my career I have often come across outdated specifications given from older applications. This could be OK, but it also happens that a valve is no longer commercial available, or replaced by newer, better and now cheaper materials, brands and constructions.

The schoolbook tell us that a valve selection should always be done from start: analyse/good description of fluid and flow (note: with possible variations over time, including dry periodes and cleaning procedures, if any, combined with available valves, materials and linings/sealings, surface treatments, checked against lifetime cost, including operation and maintenance cost.

Most of the time we can skip most of this, but time and again it is sensible to remind oneself that this is what it is all about.

Advice: Always check the origin and reason for the valve specification if something does nut rhyme! The specifications is very often based on a single persons opinion, and this person is not always an updated valve expert!

(...for larger valves in this case I would have considered a high quality stainless spindle, non wetted, combined with high-quality valve lining, and disc of ductile iron, completely protected with suitable compound.)

RE: Buttterfly valves specs .

Dear Danlap,

TSE water is clean not same sewage ! am talking about the pipes network from the plant to for example to irrigation uses !
the stainless steel is SS316 S31 and the seat AS well .

By the way , the Butterfly valves is eccentric double offsite type

Dear Gerhardl ;

The size is 300mm up to 2000 mm , PN16
i agree with you , its one man show and decision , his opinion about it that the corrosion and erosion issues !!!
i do agreed as well about the disc should be ductile iron with coated , sorry i didnt get you , what do you mean by ( non wetted & completely protected with suitable compound ))

so , what is the new specs and updated materials of that from your point of view ?


RE: Buttterfly valves specs .

Hi again

From the now given water specification, the original material specification is OK. As commented above different factories can select different technical construction and materials for the same size and pressure range. Check if the specification is an absolute requirement, or if alternative materials could be offered.

For the larger sizes weight and maintenance cost could favor the lighter in weight stainless steel combinations. I am also inclined to believe that stainless steel discs are cheaper to produce for larger dimensions, as weight for cast iron discs would be high, surface treatment (epoxy, rubber , pvc, nylon or others) would also be high. Double eccentric valves in larger size and PN16 are well suited for fabricated stainless steel discs from sheet material

SS would also protect against corrosions caused by different additives and pollutions in the water, even if the risk is low.

My suspicion is that you compete against a product line from a known (by end user) producer. It could be difficult to compete with other solutions, even if it could be sensible to use different disc specifications for smaller and larger valves, with cast discs for smaller.

Good luck!

RE: Buttterfly valves specs .

Dear gerhardl ,

Thx Again , totally agreed !
but the disc am trying to convene is ductile iron not cast iron !
therefore , any strong/convinced technical points to argue with the end users to use ductile iron disc against SS one? any proof that material will fit the requirement ?


RE: Buttterfly valves specs .

Hi Hyari,

Ductile iron is the most common material used for cast iron discs for double eccentric BFL valves, and should have been written in full as a more accurate description in my post. In my opinion this will not strengthen your case against a suitable, good quality of SS in any high degree.

Price, references, documentation of surface protection quality and thickness and evidence of long life for your valves at similar applications would in my opinion count more.


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