Re: Sodium Hypochloride service

From: <abdul>
Date: Tue Nov 06 2007 - 01:27:00 EST

Hi Shabbir

As far as i know you can simply use Carbon steel material for pipe support with plastic sheet (poly ethelene) between pipe & pipe support surface to avoid galvanic corrosion (Corrosion due to dissimilar metal contact).

Regards,
Aziz Vayani
Lead Facilities Design Engineer
Clough --- Pakistan Operation
Karachi Office

• Original Message ---- From: shabbir <shabbir@daresd.com> To: <a href="/group/PipingDesign/post?postID=54cupBb7i31YfZw0-ZhH2wFn_RtmS-AG1VX5c7ATMsybUGEN1DCLql0vTvtnnjPFX8VVRAW_ifLWpbw8EPzzoPoXDVHl">PipingDesign@yahoogroups.com</a> Sent: Monday, November 5, 2007 11:27:20 AM Subject: [PipingDesign] Sodium Hypochloride service

Hello Everybody,

Presently I am working on a Sodium Hypochloride service line. As I know that we because of the stress corrosion cracking we cannot use Austinite Steel for this service, line size is 1" to 1 1/2", we planned to use stainless steel support and with U bolt. Please guide me whether this support require any coating like titanium including U bolt please explain me this.

Thanks and have a nice DAY.

Shabbir Ahmed

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From: PipingDesign@ yahoogroups. com [mailto:PipingDesign@ yahoogroups. com] On Behalf Of Steve McKenzie
Sent: 11/04/2007 11:49 PM
To: PipingDesign@ yahoogroups. com
Subject: [PipingDesign] Re: control valves

Hi Jack

The main pitfall with three way valves is the usual application - trying to do the work of two valves with only one. It is difficult to generalise for three way valves because there can be so many configurations. However, given a "simple" type of valve you want as high an authority as practicable, for both streams, if you want reasonable control. Similar system head loss for each branch helps a bit if the valve ports are the same size. In general I try to avoid the use of three way valves unless it is a special situation with a purpose made valve, such as a boiler LCV. 3-way valves are often used in HVAC and are often seen hunting, if they havent been locked in position. hunting can normally be overcome by slowing down the response (increase P band, I time) but this reduces controllability. A smaller valve trim can often help sharpen response, but at the expense of maximum flow rate, unless the available differential head is increased.

Cheers

Steve

• In PipingDesign@ <mailto:PipingDesig n%40yahoogroups. com> yahoogroups. com, Jack Osborn <jhosborn@.. .> wrote:
  >
  > Steve.....
  >
  > thanks for the description of control valve authority. What would
  you say about similar requirements regarding three way control valves in a circuit? Should there be similar head loss (or authority) sizing? Any pitfalls to sizing a three way valve in a circuit?
  >
  > Jack
  >
  > *******
  > Jack Osborn, P.E.
  > Mechanical Engineer / Project Manager
  > Lee & Ro, Inc
  > 925 937 4050 ext 402
  >
  >
  > Hi there
  > For accurate control of simple systems it is necessary for the
  > control valve to have a fairly high head loss across it compared to
  > the entire system pressure loss. The ratio of valve loss to total
  > system (including valve) loss is called authority, and for good
  tight
  > control it should be around 0.5 (1:2) or better. A system with all
  > the head loss across the valve will have an authority of 1. An
  > authority of 0.5 means 50% of the head is lost across the valve,
  and
  > the remaining 50% is lost across the rest of the system. So for
  > control we want the valve to have a high head loss which means its
  > trim will be small, and the rest of the system to have a low head
  > loss which means big pipes.
  > So thats the reason why you see smaller that line-size control
  > valves, apart from cost of course.
  >
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[Non-text portions of this message have been removed] Received on Tue Nov 06 01:27:00 2007