7 replies to this topic

[go-fish]

What purpose does pressure information in design codes on P&IDs serve other than pipe class selection?

For Example, 150 # class piping components can be used upto 19 barg design pressure at 30 deg. C. Now if based on hydraulics, one gets DP = 8 barg (Pump shut-off) and HTP = 12 barg (assumed 1.5 X DP). Since, the pipe class is already going to be 150# rating based on this DP, does it matter if I put my design pressure on P&ID such that DP= 19 barg?

[ankur2061]

go-fish,

For piping I have never seen in any P&D the Design Pressure being mentioned. I have only seen the # rating for the piping or a alpha-numeric or numeric designation for the piping class/MOC as per the particular company's standard. Only for equipments (tanks/vessels/separators/filters/scrubbers/columns) the DP (I presume it is design pressure you mean) is mentioned. So, this comes as a complete surprise to me. For pumps, the differential head as mLC (meter liquid column) or bar is mentioned along with the driver rating (kW) & rated flow rate in m³/h. Corresponding english units may be used if applicable.

You need to take care in the design stage to ensure that your corresponding piping is of the class that can withstand the highest presure that the system (equipment + piping) can see. Alternatively, High Integrity Instrument Protective Systems (HIPPS) may be provided between connected high pressure systems & lower pressure systems to prevent the overpressurization of the lower pressure system. Systems (equipment + piping) may also be protected by providing adequately designed mechanical protection systems (relief valves).

Hope this helps.

Regards,
Ankur.

[Zauberberg]

Ankur has given very good explanation, and I doubt if anyone has come across piping design information being displayed on P&ID's: the line list and the piping class specification document are the places where all piping design information can be found. Also, if I remember well from my Design days, pressure/temperature rating is a function of Material Group and design temperature as well. So you can encounter such situation where different design temperature dictates different pressure rating for the same material, or for different materials at the same temperature.

Protection of lower-pressure rated equipment is usually achieved in both ways - by implementing IPS and by providing relief devices as an ultimate mechanical protection against overpressuring the system.

[shan]

What purpose does pressure information in design codes on P&IDs serve other than pipe class selection?

For Example, 150 # class piping components can be used upto 19 barg design pressure at 30 deg. C. Now if based on hydraulics, one gets DP = 8 barg (Pump shut-off) and HTP = 12 barg (assumed 1.5 X DP). Since, the pipe class is already going to be 150# rating based on this DP, does it matter if I put my design pressure on P&ID such that DP= 19 barg?

Hi go-fish,

A piping system consists of not only pipes but also flanges, fittings and valves. One may have various design pressure and design temperature depending his process. However it is impossible for the manufacturers to produce all kinds of customer-built pipes, valves, and fittings per each individual process conditions. Therefore, seven classes of piping: 150#, 300#, 400#, 600#, 900#, 1500# and 2500# were defined in ANSI B 16.5. In another word, the pipes, flanges, fittings and valves are standardized by the piping classes. If you call a vendor for 150# flange, he may provide you for the quotation right away. However, if you ask for 19 barg flange, I bit the sales guy will not what you talking about.

On the P&ID, usually, A is for ANSI 150#, B ANSI 300#, …, G ANSI 2500# per API. I don’t know which letter is for DP=19 barg. Do you? If you don’t either, how do you mark the line identification?

Overall, it not wrong to put DP=19 barg on your P&ID. However, just nobody does that way currently and historically. As an engineer, you had better to talk like an engineer. Right?

Shan

[go-fish]

By DP, I meant Design Pressure.

The design code I am talking about is a 3 letter alphanumeric code which are assigned to the piping on the P&ID. Each design code has a design pressure, design temperature, flex high temp, flex low temp, fluid phase and % vacuum assigned to it.

So when the line list is extracted from the system, one can get all these parameters. The hydrotest pressure is set as 1.5 X design pressure in the system and also obtained in the line list.

What I wanted to ask was that lets say in pump piping all other parameters are same and only design and hydrotest pressure are different on suction and discharge piping but still both sides are within same pipe class. How is the design / hydrotest pressure data in the line list useful in this case? Are there any other uses for this information like hydrotesting after piping erection where systems having same hydrotest pressure are tested together through isolation at specific locations and the pressure of the system is raised together?

[fallah]

What I wanted to ask was that lets say in pump piping all other parameters are same and only design and hydrotest pressure are different on suction and discharge piping but still both sides are within same pipe class. How is the design / hydrotest pressure data in the line list useful in this case? Are there any other uses for this information like hydrotesting after piping erection where systems having same hydrotest pressure are tested together through isolation at specific locations and the pressure of the system is raised together?

In pump piping may all parameters are same and only design and hydrotest pressure are different on suction and discharge piping but still both sides are within same pipe class,because both design pressures may fall into one pipe class and no class change between them!

There is a document titled "test plan" that is similar to PID and included value of
test pressure for each line along with location of blinds considered for isolation of piping sections with different hydrotest pressures in hydrotest operation.Many information to complete this document obtained from line list such as design/hydrotest pressure.
Hydrotest contractor uses that document to arrange hydrotest operation such that each line to be subjected to the same pressure specified in the document and also,as per what you mentioned,performing simultaneous operation for the sections with the same hydrotest pressure.

[go-fish]

Is there a good reference where I can get a basic understanding how hydrotest is being done after site erection? What are the implications of slightly overestimated hydrotest pressure as long as they are not exceeding the allowable stresses of the pipe material?

[asade abiodun]

i support what my fellow memebers have said.
I would like to add also that the information about the piping can be captured in its respective line number with alpha-numeric information. For instance, 4-P-B1-1010 which shows that the pipe is a 4" line for a process fluid, 300# rating (740 psig max.) and its identification number. Also, your line pressure determines the pipe rating for your pipe. Hope its meet your question.

Edited by asade abiodun, 30 March 2010 - 05:55 AM.