How to prepare piping class document? 1

[Amanda123]

Hi all,

I have been assigned the task of preparing a piping class document for a new greenfield project. As my background is in process engineering, I would appreciate your guidance on how to create this document, especially since there are no piping specifications provided by the client.

Any advice or recommendations on how to approach this task would be greatly appreciated.

Thank you!

Best regards,
Amanda

 

[LittleInch]

Your best bet is to find one from a different project.

But if you want to start from scratch first work out how many you need. Easiest is to do them for each flange rating you have.

 

[ShabsRBI]

Hi Amanda,
Preparing a piping class document is a complicated issue as this depends upon number of factors. Important factors used to create a piping class are as follow
1. Flange rating: Based on ASME flange ratings #150,#300,#600,#600
2. Temperature rating: -29 Deg C to 260 Deg C
Temperature rating : -49 Deg C to 260 Deg C ( Impact tested CS material to be used)
Temperature rating : 261 Deg C to 450 Deg C
Temperature > 450 Deg C

3. Extent of NDE requirements: 5% NDT Radiography or 100% NDT Radiography
4. Corrosion Allowance : 1.5mm, 2.5mm or 5mm depending upon the corrosive service.
5. Process Conditions : Utilities like water, air, nitrogen
Boiler Feed water, Condensate and steam : Low Pressure, Medium Pressure and High Pressure
General Hydrocarbon ( <0.5% Suphur)
General Hydrocarbon (>0.5% Sulphur)
General Hydrocarb (1-3% Sulphur)
Hydrogen
Hydrogen with Hydrocarbon
Catalyst
Acidic Service : Sulphuric Acid, Hydrochloric Acid
HF Service : Low Temperature, HF vapour ( High temperature - Monel)
Sour Water
Amine Service
Any other specific Service like High temperature Reactor products with corrosive constituents.

Once these categorization are done then possibly it will give a good start to form the piing class.

 

[shvet]

PIP has published classes for industry reference

Code-Compliant Practices for Engineering Disciplines | PIP

Process Industry Practices offers applicable practices for several disciplines, including refractory, piping, and electrical. Find your material specifications.

pip.org

 

[NovaStark]

In addition to what was already mentioned, if you can get ahold of the PIP pipe specifications, you can use them as a starting point.

Another important aspect is the metallurgy of what is being used. Usually, you would have a material selection diagram to go preceed your pipe spec generation which would highlight the general ratings, what nominal materials to use, etc.

 

[Snickster]

So what it appears you have been tasked to determine what individual Piping Material Specifications Sheets are required for the entire plant including process and utility piping. Each specification sheet provides details on piping materials, wall thickness, reference ANSI industry standard, end conditions (welded, screwed or socket weld) etc., and pressure and temperature ratings. I believe for now they just want you to make a list of all the individual piping material specification sheets that will be required and later to actually write specifications or purchase such as are available from PIPs.

One way to start is to get a copy of the process and utility P&ID (piping and instrumentation diagram) which shows all equipment and connecting lines. Each line will have a given service and will require establishment of a pressure and temperature rating, and materials of construction so to be compatible with the fluid contained. Maximum system pressures and temperatures typically come from the system process engineer through development of the PFD (process flow diagram). The PFD should list maximum expected pressure and temperature of each flow stream. Also discussion with the process engineer who developed the PFD should be performed for his agreement on what the maximum design pressure and temperature should be and maybe a HAOP is required to pin down the design pressure and temperature for each line.

Piping Material Specification Sheets are rated in in accordance with ASME B16.5 flange pressure class 125#. 150#, 300#, 600#, corresponding to the pressure and temperature rating of the class flange. For instance B16.5 Class 150 carbon steel flange is rated for 285 psig at 100 F so this would set the design pressure and temperature of an individual Piping Material Specification Sheet for a Class 150# rating. Most of the time you can use the same Piping Specification Sheet for different services as long as the material is compatible and the pressure and temperature rating of the piping specification sheet is equal to or greater than the design pressure/temperature of the line in service. Carbon steel is mostly used material, then stainless steel for corrosive service then more exotic materials for highly corrosive service.

I will see if I can find some examples of piping material specification sheets in my files and post later. I assume this is the same methanol plant you indicated in another post so I will see if I can find related specs.

 

[Snickster]

Here is a link that discusses Piping Material Specifications:

Guide to Piping Specification, Piping Classes, and Piping Material Specification | What is Piping

Piping Specifications are engineering documents, generated by design consultancies to define design and construction requirements applicable to a specific product or application. They provide specific/additional requirements for the materials, components, or services that are beyond the code and...

whatispiping.com

In this link a reference to a Piping Class sheet is what I call a Piping Material Specification Sheet which is a list of piping components in tabulated form with materials wall thickness, end type, etc and is usually about 1 to 3 pages long. There is an individual piping Class sheet/piping material specification sheet for each rating class and material of construction. A Piping Specification is the document that all the individual Class sheets are attached to. It has all more specific technical requirements for all components of the individual Class Shee in paragraph form. Each line on the P&ID will be identified with a line number that includes a designation of the associated piping material class sheet that it will be constructed of.

Attached is an example of a piping material specification/class sheet

 

[pierreick]

Hi,
Consider this document to support your work.
Good luck,
Pierre

 

[Amanda123]

Thank you all for the reply. I have my operating condition only. Is that below method correct for determine process design pressure and temperature at first:

Design Pressure and Design Temperature

Generally, the design pressures and design temperatures are taken as below (as minimum):

Design pressures = MOP + 10% margin or MOP + 72.5 psi (whichever is higher)

Design Temperature = MOT + 10 °C


Some exceptions to the above include the following:
Minimum design pressure of 50.75 psig for low pressure systems that are connected to the LP flare or vent system
Minimum design pressure of 100 psig for systems that are connected to the HP flare or vent system
For equipment operating at ambient conditions, the maximum design temperature should be designed for black body temperature which is 65 °C.

 

[LittleInch]

One of my pet hates is when some nominal number in one set of units is then converted into another se tof units with ridiculous accuracy.

So in this case, the DP is MOP plus 10% ( A bit tight to be honest, but probably good enough to avoid relief valve simmering) or MOP plus what is actually 5 bar. Ditto the min pressur eis actually 3.5 bar.

Both nominal numbers. If you're going to be defining your system in psi then use nominal psi numbers, not some false equivalence so use 75 and 50 if you want to do it this way.

But setting DP by MOP will give you a wide set of piping classes.

Most piping classes just go to the maximum DP the particular flange rating has for the design temperature or has a table listing design pressure for different design temps and then you take you pick from piping class 1A, 3A, 6A, etc relating to class 150,300,600.

 

[pmover]

to supplement Snickster posting . . .

the Valve codes on the pipe spec sheet refer to Valve data sheets that provide valve specifications. For example, valve type, materials of construction for each valve component, valve bonnet/body, size, end connection type, service temp range, applicable standards, seal/gaskets, etc.

 

[Amanda123]

Thank you, everyone. I have now established the pressure rating based on the design pressure from the MOPX1.1 above. However, I still have some doubts regarding whether the ANSI pressure ratings for Carbon Steel (CS) and Stainless Steel (SS) are the same?, as outlined below.

ANSI Pressure Rating for Carbon Steel (CS) and Stainless Steel (SS) Flanges at 100°C (212°F)​

Class	Carbon Steel (CS) Pressure Rating	Stainless Steel (SS) Pressure Rating
Class 150	19.6 bar (285 psi)	19.6 bar (285 psi)
Class 300	51.0 bar (740 psi)	51.0 bar (740 psi)
Class 600	103.4 bar (1,500 psi)	103.4 bar (1,500 psi)
Class 900	155.1 bar (2,250 psi)	155.1 bar (2,250 psi)
Class 1500	258.5 bar (3,750 psi)	258.5 bar (3,750 psi)
Class 2500	430.8 bar (6,250 psi)	430.8 bar (6,250 psi)

 

[GBTorpenhow]

They are not the same as they are different material groups. See ASME B16.5 (ANSI hasn't been associated with B16.5 for quite some time now). Double check these numbers too, Group 1.1 carbon steel should be 1480 psig for Class 600.

 

[Snickster]

The attached provides typical guidelines for setting design pressure and temperature, some may be over conservative so use your judgement.

 

[Snickster]

Typically the pressure vessel design pressure is set by the process engineer based on allowing for a certain % pressure above the MOP so that the relief valve does not activate except in upset conditions. This % is a minimum of 10% above MOP but can be higher depending on the process and expected upset condition pressure swings and how often they occur. Likewise the design temperature is also set at a given % above MOT. The guidance for setting the design P-T of the pressure vessel is found in the pressure vessel specifications of clients such as the one attached.

Once the pressure vessel design pressures-temperatures have been set then relief valves are provided on vessels set at the design pressures and design to produce the required flow at the design temperature. The piping specifications pressure and temperature ratings match the vessel P-T ratings not the other way around.

 

[Snickster]

ASME B16.5 Stainless Steel flange pressure ratings are less than carbon steel flange ratings and even different grades of stainless steel have different MAWP. B16.5 ratings are related to a specific material group and provides tabulated pressure versus temperature ratings for each group.

 

[ShabsRBI]

What is the reason for SS flange pressure ratings less than Carbon steel flange ratings at given temperature? I have tabulated the Pressure rating from ASME 16.5 (#150 Flange) and for all the temperature Pressure ratings of CS>SS.

Pressure Rating - Kpa
#150 Flanges
Temp (Deg C)	CS (Group 1.1 )	SS 304 ( Group 2.1)
-29 to 38	1960​	19​
50​	1920​	1830​
100​	1770​	1570​
150​	1580​	1420​
200​	1380​	1320​

 

[LittleInch]

Because the material strength is a little bit lower?

Not many people use kPa in piping design ( it kind of shows you have a background in process engineering....). It tends to be bar, psi or the Indian subcontinent seems to like kg/cm2. It confused the daylights out of me as I thought it was psi...

Amanda - Thank you, everyone. I have now established the pressure rating based on the design pressure from the MOPX1.1 above. However, I still have some doubts regarding whether the ANSI pressure ratings for Carbon Steel (CS) and Stainless Steel (SS) are the same?, as outlined below.

You should have doubts. It's ASME, not ANSI and the data you have is incorrect. You seem to have used material class 1.2 for the carbon steel and the stainless values are lower, depending on what material you choose. Did you just use the first google result you got?

I do fear that this task is well outside your current skill set and experience and you could make some very serious errors here without actually knowing it. Please report back to your management and say that you investigated this and its much more complex than it might first appear and you need someone with more experience and knowledge about piping systems to help you. If your company is involved in this type of work I simply do not believe they do not have access to either existing, similar piping specs which can be checked and adjusted for your process conditions or fluids or people who are able to do this or find this information. You really should not be starting from scratch and making complete novice errors like the table you posted. This could have very serious consequences if you get it wrong.

 

[ShabsRBI]

This information is straight from ASME B16.5. Please find the following tables.

 

[Amanda123]

above table was correct. Thanks all. Somehow i have completed ansi class as per design condition. Thank you all