Pressure Containing vs Pressure Retaining Parts 3

[danice]

May I know what does it mean by "pressure containing parts"? And What does it mean by "pressure retaining parts"? What is the difference between "pressure containing parts" and "pressure retaining parts"? Very appreciate if anyone can help.

 

[BigInch]

I would define as such,

Pressure Containing Part: Withstanding or "containing" a (internal) pressure without leakage, as would a pressure pipe, valve body or pressure tank.

Pressure Retaining Part: Holding a pressure, but without actually "containing", or stopping flow entirely, as would a stuffing box or a labyrinth seal. Also it might be a part that could hold pressure under, inside, or to one side of it after an external, body, or primary pressure had been released.

http://virtualpipeline.spaces.msn.com

 

[JLSeagull]

Both sound a lot like the same thing to me. These phrases and the associated PMI or material certification increased in use over the last dozen years or so, especially related to international projects. I suspect that these exist in some code or standard - some that I lack familiarity.

I buy some Coriolis flow measurement instruments that include secondary containment. The secondary containment lacks the full ASME flange pressure and temperature rating. However, upon a rupture of the element it may prevent a spill or release up to a pressure well below the body rating.

 

[jte]

One way to think about it is to consider pressure vessel with a stiffening ring for either vacuum (external pressure) or at a conical transition. While the ring is not a wetted surface and therefore does not directly contain the pressure, it is a structural member required to retain the pressure. Similar situation with a reinforcing pad on an opening. But in reality, "pressure containing" and "pressure retaining" are often used interchangably.

jt

 

[SJones]

In what specific context has the terminology appeared so that we can give you a more definitive answer?

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[danice]

SJones,

I would like to understand the terms apply on valve. Thank you

 

[abscott]

danice,
I know of no document that makes a distinction between "pressure-retaining" and "pressure-containing" parts and I agree with jte's last sentence. In the real world these terms are used interchangeably.

In theory, if you have a section view of a valve assembly that is internally pressurized, any part that you erase that would allow the pressure to escape would be considered and pressure-containing part.

Having stated this, some parts, such as bodies, bonnets, cover flanges etc. are strictly governed by design codes and standards published by the ASME/ANSI (or agencies in other countries). Some parts that may be cosidered pressure-containing, such as stems, shafts, packings and seals may not be covered by any design standards.

This can be a complex issue depending upon the valve style and the applicable codes and standards. If you have a specific question please add some details and we will attempt to answer your question.
Hope this helps.
ABScott

 

[Anarchy]

I would say "containing" parts are vessels, bodies, tube etc.

And "retaining" parts are the bolting, studs, nuts, clamps etc. holding the containing parts together.

 

[JLSeagull]

Anarchy's explanation relates to other common terms such as "wetted" vs. "non-wetted" components.

 

[proinwv2]

I agree with "Anarchy's" simple definition. However, being a valve designer for 40 years, I can't offhand remember a code defining these terms.

To retaining, I would add bonnets.

Paul Ostand

http://www.ostand.com

 

[JAlton]

I use these terms strictly relating to Pressure Relief Valve Parts. A simple method of teaching the difference between Pressure Containing Parts and Pressure Retaining Parts to a classroom is the use of a mnemonic device, Pressure 'Conta'ining Parts come in 'Conta'ct with the fluid. Pressure retaining Parts do not come into conatact with the fluid. In a pressure relief valve only the parts which are in contact with the fluid while the device is closed (not relieving pressure) are considered "primary pressure zone" parts [ASME Code Sec. I & VIII]. The primary presure zone parts are "pressure containing". The Spindle, spring, spring washers & compression screw hold the disc closed aginst the nozzle. These are "pressure reataining" parts. The Body & Bonnet and the fasteners which hold them together are also "pressure retaining" parts.

JAC

 

[gr2vessels]

API 674 definition of Pressure-containing parts and the pressure-retaining parts:

Clause 1.4.1 7 A pressure-containing part is a part that acts as a barrier between processo r motive fluid and thea tmosphere. Such parts include, but are not necessarily limited to the liquid cylinder, the discharge manifold, the suction manifold, the stuffing box, cylinder plugs and covers (when in contact with process fluid), valve seats (when a portion is in contact with the atmosphere), the gas cylinder, the gas cylinder head, the valve chest, and the valve chest cover and heads.

Clause 1.4.1 8 A pressure-retaining part is a part whose failure
would allow process or motive fluid to escape to the atmosphere. In addition to the pressure-containing parts listed in 1.4.17, pressure-retaining parts include, but are not necessarily limited to, liquid and gas cylinder bolting, stuffing box bolting, gland bolting, glands, and covers that constrain plugs and valve stops. Not included in pressure-retaining parts are parts such as packing, gaskets, pistons, plungers, piston rings, rods, valves, seats (when completely surroundbeyd pressurecontaining
parts), and internal bolting.

Does anyone have an ASME reference for the above definitions, having just hit the wall with a fabricator refusing to accept this definition not sourced from the Code, but a standard only...
gr2vessels

 

[JLSeagull]

I would not try to apply the definition in a recip pump standard for all "pressure containing" components in everything. However several other API standards apply that phrase. Some are codes like the pressure vessel inspection code but it lacks a definition.

I checked API 579 - fitness for service uses examples but no real definition. API RP 582 Welding Guidelines includes the following:
"Pressure-containing equipment (such as pressure vessels,
heat exchangers, tankage, piping, heater tubes, pressure
boundaries of rotating equipment, and attachments welded
thereto)."

API RP 582 uses the phrase pressure retaining without a definition.

 

[monofm4m]

I would present one more reference of "Pressure-containing Parts" definition. It is NACE Standard MR0175 (Let me go up to and incl. "2002" edition).

Quoted, "Those parts whose failure to function as intended would result in a release of retained fluid to the atmosphere. Examples are valve bodies, bonnets, and stems.", Unquoted.


The above is not direct response to this thread. So, I would add my own response below,

"containing parts" and "retaining parts" are to be understood as same meaning at the viewpoint whether or not, a failure of parts (e.g., body, bonnet, cover, seat ring & closure member <-- if valves used as dead-end service) results in releasing pressurized service fluid outside of spoken pressure unit (e.g., valve, pump, vessel).

However, gaskets and seals should be exempted from those terms, by their nature. These parts are produced to act against "pressure", thus unnecessary to be categorized into "containing parts" nor "retaining parts" again.


I hope that I am not far a way from others in interpretation.


monofm4m

 

[sterl]

The National Board of Boiler andd Pressure Vessel inspectors had the (2) definitions in some of their primary standards; and I believe they actually were derived from language in the 5th chapter of the ASME VIII.

i have neither with me at the moment but I know that in sorting out test results and quality assurance issues with the National Board they make specific reference to portions of a Safety Relief Valve as pressure containing, and others as pressure retaining. Much like the post from No Soup above.

There is also "pressure defining element" in a B & PV Sense but thats another can of worms.