4 replies to this topic

[R NESAMANI]

Dear all,

 

I have to replace one 18'' ball valve with 18'' globe valve in 18 inch natural gas pipeline.

We have to supply gas from one pipeline-1 operates at 85 kg/cm2 to other pipeline-2 which operated at 60 to 70 kg/cm2. We have two ball valves separating these two pipelines. So we are planning to replace one ball valve with globe valve for supplying gas from pipeline1 to 2.

Can anyone help me in giving a detailed tender specification to procure this globe valve?

 General parameters are as below

 

Item

Value

Design Pressure

92 kg/cm2

Design Temperature

-20 to +60 Deg.C

Size

18 inch

Class

600

Operation

Hand wheel

 

 

End connection

Flanged

Service

Natural gas pipeline

 

[Art Montemayor]

 

 

The best and most efficient way to issue detailed equipment specifications and protect your company and yourself from incomplete and wrong specifications is to issue a Data Sheet on the subject equipment - a large valve in this case.

 

You can design and build your own Data Sheet if you are unable to download one from major valve fabricators.  I would inquire with all the valve fabricators you can, requesting a version of their Data Sheet(s).  You will find that fabricators are very much interested in obtaining detailed and accurate descriptions (as well as Scope of Work) for their equipment because this is in their interests as well.  Neither they or you want to get involved with lawyers in a legal argument after you have signed a purchase order.  Data Sheets are meant to avoid such a costly and negative situation - and a Data Sheet condenses all the pertinent and important details that you want or need for your application.  The point here is that you have the legal obligation to define what, exactly, it is that you want to purchase.

 

As an example, you need to go into the details of specific details and description of such items as the flanged connections, citing standards or codes.  You need to describe the basics: materials of construction, the MAWP (and MAWV if applicable), operating/maximum/minimum operating temperatures and pressures, types of seals and their materials.  A complete fluid composition may be needed/requested if the seal materials are to be specified for the service.  Some plastics or polymers may not be recommended for the service - depending on the fluid and the tempertures/pressures.

 

Do you require manual or pneumatic/hydraulic operators?  How do you intend to manipulate such a large and heavy device?  Do you require an indication of when the valve is open or closed - and if so, is this to be monitored on a differential scale?

 

Basically, obtain some valve Data Sheets and start reviewing them.  If you can’t obtain them, then you have to take the initiative and construct one.  That’s what engineers are supposed to do - solve problems.

[Neelakantan]

ART has given a detailed reply pointing the ways to engineer a solution for the problem;

 

as a project consultant, i have some queries before you can replace a 18" ball valve with a globe valve!

q1) how much gas is being sent;

q2) what is the quality of the gas and what happens to the phase envelope when the pressure is reduced

q3) using  a handwheel operated valve? how the pressure drop is regulated and conversely how the flow is measured or regulated;

q3) what is the holdup of the two lines; how the pressure hold-up /packing will be monitored when the flow varies?

q4) as ART has pointed out indirectly, have you been looking at the pressure control loop?

q5) has a HAZOP /safety case analysis  been carried out on the proposed supply methodology? how about a high pressure indication for shutting down? are the ball valves manually operated or they have actuators?

 

 

 

regards

neelakantan

[R NESAMANI]

Thank you for your replies.

 

Mr Neelakantan, the point wise replies for you are as below

 

1) Gas flow will be from 60,000 scm/hr to 200000 scm/hr

2) Dry gas & no phase change happens in gas due to pressure reduction

3) We will control the flow. Pressure drop can happen in globe valve

4) To monitor pressure, we have pressure transmitters

5) No, we don't want pr. control loop. As its a cross country pipeline. We only give flow for filling the pipeline. nothing will happen if my valve malfunctions for some duration.

6) No need of the shutdown device. As it takes long time to fill the pipeline.

[Neelakantan]

thanks for the reply;

 

1) per point 1 and 6, the flow is varying; and probably depends on the withdrawal; that is why i asked about packing/depacking of the line;

2) yes a globe valve can reduce the pressure and the pressure drop depends on the flow; per point 3, you mentioned you "control" the flow; is it a direct action? or you mean that  you will pack / unpack the second line depending on the withdrawal?

3) what are the design pressures of the two lines?

 

regards

neelakantan