Why 2000# threaded fitting are not covered in ASME B16.11

With ref. to your query on 2000 class fittings, I would like to highlight that those low pressure fittings have become more absolute in application.
Those fittings are finding very less use in low pressure drainage/sewer systems.

Answering yours and additional questions,

1) The 9000 lb fittings in NPT threading is beyond the permissible leakage allowance and so is why NPT threaded fittings are not available in that range. But other threading type can withstand higher pressure, which is how compression/threaded fittings work, like swagelok.

2) For 2000 lb fittings, socket welding is not available, as threaded fittings are sufficient enough for that pressure class. And socket welding such thin pipes is not economical/recommended due to the special care/skill required or the practical difficulty on alignment issues.

3) Cap & coupling were not convered in B16.11even when the MSS SP 49/50 was first encompassed into it and 4000 lb was eliminated due to the lack of support in the Americal industry. If you are using 2000 lb piping fitting, plugs are to be used against caps and unions against couplings.

Above all these, the most important fact to be considered is of the market trend and industry acceptance. For instance, min. pipe sch is STD / 2.24mm for 1/4". The pressure it can withstand is around 2000 lb discounting NPT threading. But it has become a practice to use 3000 lb and not 2000 lb.

Moreover to what I have seen, the prices difference is nearly nil between 3000 and 6000. 9000 is around 5 to 10 % higher than 6000. ofcourse it depends on the quantum you purchase.

Regards,
Kannan.


Dear all,

 could anyone explain that threaded fitting i.e. cap & coupling of class 2000  are covered in which standards?
 
because ASME B 16.11 , covered the forged threaded fitting (i.e. Tee, elbow and cross) of class 2000, 3000 and 6000.
But threaded cap,half coupling and coupling are covered from class 3000 and 6000.  
 
Regards,
Vinayak

Locking devices.

Very interesting note from Surve on CSO/C.

May be it would also be interesting to discuss on interlocking devices also at this point of time.

To the extend I have come across I would classify as below.

1) The normal valve locking devices which are used to have the valve locked in open or closed position on an individual basis.
2) The interlocked valve system where a group of valves are kept in open or closed position to achieve one or multiple different stream flow conditions in a chemical process.
3) The interlocked valve system where a group of valves in the upstream and downstream of one or group of Pressure Safety Valves for safety reasons.
4)  The interlocked valve system where a group of valves are kept in open or closed position and interlinked with electronic locking keys to obtain a swing in production of a plant like a switch between LLDPE to HDPE production based on the market demand and sales conditions.
5) The completely integral electronic interlocking system of valves to obtain a swing which are more sensitive and time framed.

The devices ranges from normal padlocks, integral locks in the valve design itself, external retrofit locking device and electronic locking devices using position sensors in campanion with MOVs.

The interlocking at times may involve as high as 30 different valves in one single network.

I find some companies apply the individual locking devices for PSVs, which is really not a safe solution. I feel the interlocking is required for PSVs so that even accidently the valves are not locked in wrong positions.  Moreover the Master keys are in the control of the plant manager and are obtainable only with proper authorisation for changing any of the valve positions. This is the same concept of CarSeal. This is one reason why we find very less engg. companies are prefering to have the above locking devices rather than the CarSeals.

The logics of locking operation are to be part of the Plant operating manual in my opinion. But rarely implimented.

Members who have used locking devices and systems for other purposes are also requested to share.

With regards,
Kannan

Car seal open / close.

CSO Valves are normally used in PSV lines and they are supposed to remain open even in case

of its stem failure. So it is preferable to orient them in horizontal.

More on CSO Valves :

Regards,

Jitendra Surve

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From: piping_valves@yahoogroups.com [mailto:piping_valves@yahoogroups.com] On Behalf Of Paranjape, Deepak V
Sent: Friday, July 25, 2008 9:17 AM
To: piping_valves@yahoogroups.com
Cc: kannan.sundaram@linde-le.com
Subject: RE: [piping_valves] How do bellow valves work ?

Hi all,

During a recent client design review, the client (Exxon Mobil) asked us to orient the stem of all valves with CSO (Car Seal Open) in horizontal position. Can anyone share the reason for this. Is it a thumb rule or it just client specific choice.

Deepak

PWHT - Caustic service

I hope some may be knowing the company named Denora SpA which was once a world leader in Caustic plants and had developed new electrolyser technologies which is used to produce NaOH from high conc. saline water. As per thier experience, PP piping, PP valves and PP coated pump casings and GREpoxy resin based equipments and tanks were used for NaOH conc. is greater than 20% irrespective of temp. For conc. more than 90%, especially in caustic flaking plants, Complete system is made of proprietary Nickel alloys especially of Outokumpu of Finland.

Sriram of the group may contribute more who has extensive knowhow in this area of caustic service.

With regards,
Kannan

"Bathula Raghuram \(Mumbai - PIPING\)" <R.Bathula@ticb.com>

At temperatures above ambient, corrosion rates of carbon steel become greater and is accompanied by a risk of caustic stress corrosion cracking (CSCC). Low concentrations of caustic can be safely handled by carbon steel up to 180^oF/82^oC, where CSCC starts to become a risk factor, while the safe upper limit for a 50% solution is approximately 150^oF/65^oC, although cracking has occurred at temperatures as low as 120^oF/48^oC. The Caustic Soda Service Graph (attached pic) is a widely used guide for determining safe operating temperatures with respect CSCC of carbon steels at various concentrations of caustic.

Conclusion: PWHT generally recommended by process designer for CS used caustic service, mainly based on two parameters, concentration of the solution and operating temperature.

Darji Nilesh (Mumbai - Machinery)

In Process data sheet, Process has asked to perform PWHT for Centrifugal pump Material due to caustic service.
Pump casing material is A 216 Gr WCB.
Can any one clarify why It is required !! any specific reason !!

Regards,
Nilesh.

Reduced Rating

Reduced rating is common where a conservative approach is applied in defining the piping materials while shaping the piping material classes.
Conservative... in the context of reduced thickness of pipes and fittings and having in some cases a reduced pressure rating of flanges. Subjectively, handling such cases is a little bit complex due to the nature of broad aspect of the parameters involved.

In a process plant, there will be few border cases of design conditions in the process streams, by which I mean the borders of the ANSI B16.5/B16.34 rating tables. On certain cases reducing to the next lower pressure rating will benefit a turnkey contractor, considering down the line cost benefit depending upon the quantum of piping involved in those streams. During such cases the piping material engineer who optimizes the PMC-piping material class concludes with process engineer to reduce the design condition.

In these border cases there are two aspects.
1) The simple safety factor reduction of the process condition judged by the process engineer.
2) The process stream may not be subjected to the defined design condition continuously, but on a cyclic or only for a short period of duration. ANSI B31.3 / 1 allows such temporary surging under certain criteria (Refer the code for details). Under such limitations, the piping material engineer works/designs the PMC with reduced pressure rating conditions also called as a STC - short term condition.

So in conclusion such conservative approach helps in avoiding Over Designing the piping system with the ANSI code as an excuse/backing. Addtionally, such concept has significance when the quantum of piping is extremely high and if the streams are in higher temp. ranges where material selection plays a very important role.

With regards,
Kannan

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Can you please explain about " Flange Reduced Ratings".

Regards

Srinivasa Murthy