7 replies to this topic

[jprocess]

Dear All,

There are some common hints on P&ID development which I do not know about the reason or concept behind of them. They may be resulted from experiences of companies in big projects. Some of them are as follows:

1. Type of isolation blinds shall be as follows:
a) Spectacle Blinds: 10 inch and smaller
b) Ring Spacer and Spade Blind: 12 inch and larger

2. Gate Valves are recommended isolation valves of 8 inch and smaller size for water service while Butterfly Valves are recommended for 10 inch and larger size for water service.

3. A angle type valve shall be applied for services with high differential pressure.

4. Type selection of strainer:
Y-Type Strainer: 3 inch and smaller
T-Type Strainer: 4 inch and larger

5. A stop check type valve shall be installed on the steam generator outlet line.(What is stop check valve?!)

Let me know your experiences regarding to above mentioned points.

[HMAlmosa]

1. Type of isolation blinds shall be as follows:
a) Spectacle Blinds: 10 inch and smaller
Ring Spacer and Spade Blind: 12 inch and larger

Sorry I have experience with only your first point. A spectacle blind become too bulky and heavy for 12" and above. That is why it is broken to 2 pieces (ring spacer and spade blind).

[fallah]

[quote name='jprocess' date='May 31 2008, 12:01 AM' post='19101'
5. A stop check type valve shall be installed on the steam generator outlet line.(What is stop check valve?!)
[/quote]
Refer to:http://www.tpub.com/content/construction/14265/css/14265_126.htm
You can find useful and brief information.

[Jatin Shah]

I can answer some of your questions.

1. Isolation blinds:
12" and above Ring spacer and Spade blind is used as it becomes very bulky with spectacle blind which is a 8 shaped object. It will not be easy to rotate and fix the desired duty of open or closed as required. With 10" and smaller it is manageable to rotate the spectacle blind.

2. Water isolation:
For isolation purpose gate valves upto 8" are used because of ease of operation. Above 8" it becomes difficult to turn the spindle manually. But that is not the case with butterfly valve and hence are preferred for bigger sizes.

Regards,
Jatin Shah

Dear All,

There are some common hints on P&ID development which I do not know about the reason or concept behind of them. They may be resulted from experiences of companies in big projects. Some of them are as follows:

1. Type of isolation blinds shall be as follows:
a) Spectacle Blinds: 10 inch and smaller
Ring Spacer and Spade Blind: 12 inch and larger

2. Gate Valves are recommended isolation valves of 8 inch and smaller size for water service while Butterfly Valves are recommended for 10 inch and larger size for water service.

3. A angle type valve shall be applied for services with high differential pressure.

4. Type selection of strainer:
Y-Type Strainer: 3 inch and smaller
T-Type Strainer: 4 inch and larger

5. A stop check type valve shall be installed on the steam generator outlet line.(What is stop check valve?!)

Let me know your experiences regarding to above mentioned points.

[djack77494]

The items you discuss tend to be preferences within the organization or plant, and can vary from site to site and client-to-client.

In a sense, a spectacle blind is really just a spacer and spade bline welded together. It appears that your site (perhaps at some point in the distant past) decided that above 10" a spectacle blind became unwieldy to deal with. It is easier to deal separately with the smaller and lighter spacers and spade blinds instead. I do not favor this approach since you lose some of the advantages of going with a spectacle blind, but many make this same decision.

Butterfly valves are a low cost/minimum space alternative to gate valves for isolation purposes. Except for high performance butterfly valves, they are inferior in that they do not provide the robust isolation that a gate valve can provide. Nonetheless, for non-critical services, and especially for large line, the savings is significant, and butterflies are often chosen. Though I know of instances where your items 3 & 4 are endorsed, I personally do not like T-Type strainers in large lines, and see no reason to force an angle valve where an inline valve designed for a large pressure drop would suffice.

Finally, while I don't know the history, I do know that stop check valves are commonly installed on steam generators. They make sense, functioning as a check valve (NRV) while having a handle permitting the operator to "force" the disk into the closed position. Two functions, one valve. I think it's just that simple.

Doug

[Qalander (Chem)]

Dear Mojtaba, May I tip in with my humble general comments

It is dependent on criticality of service or importance with repect to; 'Point Pressure, temperature& process stream state Condition to decide or detemine the issues raised. Accordingly the suggested size related rule of thumbs might not be appropriate and safe in general terms rather we have to decide on case to case basis.

At times maintenance and handling ease supersedes the design basis,whereas in other circumstance operability ease may over-ride.
Hope these general comments are not duplication and do add some help.

Best regards
Qalander

[jprocess]

Dear All,

Thanks a lot for your valuable comments. I really enjoyed them and found them informative.
Hope to see other comments from other experts, here.

Cheers.

[GMP]

Well the stop check valve is the safety of boiler. anyways when u discuss the boiler outlet lines do consider the isolation valve provision on it and never miss the provision of balancing line to connect to main header. Without bypass U wont be able to connect.
thanks