Service is rich amine , pipe falls in class 300# with moc as A312 TP304/304L seamless (Sch40-3/4”-PE) , corrosion allowance is 0.063” , Dgn Pr. & Temp. are 520 psig & 288 F , Pipe is SW for small bore. Since Gate valve size is ¾” so it should be SW but what should be the rating – 800# or 300# ?

Regards
PME

valve rating shall be same as pipe rating 300#

mkhan

Or
Slight re-phrasing 'Pipeline and Valves should have same/Compatable ratings'. as otherwise will not suit the intended services.
Regards
Qalander

Sachin,

Per the MOC described, the pipe MOC in laymans language is stainless steel (SS) (Type 304).

Question 1: How come you have described a corrosion allowance for SS 304 material? Stainless Steels are not given a corrosion allowance.

Question 2: You have presumed it to be SW (Socket Weld) just because it is 3/4, which I don't agree with. It can be flanged or SW depending on the service and operation requirements.

Per my understanding when SW fittings and valves are used, many companies prefer to go for a higher rating for the SW fitting/valve compared to the connecting pipe.

Maybe some other people can shed more light on the subject.

Regards,
Ankur.

Dear Sachin,

There are several standards for Pressure – Temperature ratings of valves. While you have given the specs for the pipe, you have not given the MOC of the valve chosen. Based on the MOC, the valves are rated for various pressures at different temperatures. Reputed manufacturers generally provide the P/T ratings of valves manufactured by them. For one such table, please visit: http://www.documentation.emersonprocess.co...lves%0ADivision

Assuming that you would be going for Stainless Steel valves, the rating chart shows a working pressure of 530 PSIG at 300^o F, for SS 304, for class 300# valves, which is just about OK. In case of any doubt about the working conditions, (i.e. in case they are likely to be more severe), you should opt for the next higher rating. Such P/T ratings are available for pipes also. However I wouldn’t worry much about them as Sch. 40 seamless pipe (TP 304) would withstand much higher pressure at 300^o F – may be around 2000 PSIG.

Regarding SW ends of the valve, Ankur is right. Flanged valves can very well be used; but if the industry standard (In your organisation) is SW for small bores, it is perfectly OK too.

I'm no welder, and I know that a socket welded connection is not as strong as a full penetration butt weld, but I think the SW connection would definitely NoT be the weak point in your pipe spec. In other words, its pressure holding capability should (easily) exceed that of the 300# flanges in this pipe spec. (BTW, the flanges SHOULD be the weakest point of the pipe spec unless otherwise noted.) I'm a bit confused by your sort of insisting on knowing what the valve's "rating" is. Flanges fall into ASTM/ASME classes-they have "a rating"; valves do not. Valves may or may not have connections that would fall into such a class. A SW connection would NOT fall into a class.

Like flanges, valves also have Pressure – Temperature ratings. There are several standards dealing with this. (ASME, API, MSS, etc.). Other than the end connections, the valve seating, stuffing box, body etc. should be designed to withstand the pressure at the specified temperatures.

Vogt Catalogue, for example, gives the pressure Temperature ratings of their valves at the following site.
http://www.flowserve.com/vgnfiles/Files/Li...VACT0000-01.pdf

Manufacturers may not give products to each one of the ratings. Particularly the smaller valves are generally rated for higher ratings. In such valves, if provided with flanges, only the drilling is made to suit the duty class for which the valve is ordered. However for larger sizes, valves are designed for different classes as per the manufacturer’s standards and the materials are chosen accordingly.

OK, Ram. I got a bit sloppy in how I was using words. What I meant in my comment about valve ratings was then you don't have the type of uniformity that you would have for flanges. Any 150# RF flange purchased will (unless defective) have temperature and pressure holding capabilities as defined in the ASTM/ASME Pressure-Temperature Ratings tables. So I can look up for my Group 1.1 material, a 600# flange at 500 degrees F and see that it can withstand 1135 psig. Doesn't matter where in the world I buy it or who the supplier is. My intent was to suggest that this is not true of valves. Different manufacturers manufacture different valves, and I cannot refer to some standard table to tell me what manufacturer A's valve is designed for and then expect that manufacturer B's valve has the same P-T withstanding capabilities. Or am I mistaken and are there standard tables similar to those for flanges?

BTW, thanks for that useful link.

Thanks, Doug,

You are right. While it is possible to just look at a flange (perhaps take a few measurements) and recognise the flange rating, it is not possible to do so as easily in the case of a valve. There are specific requirements for the valves to satisfy, to be graded as class 150 etc., as per the standard, e.g. http://www.engineeringtoolbox.com/temperat...ves-d_1182.html but it is left to the manufacturers to carry out their own design and dimensioning.

As a result, it may not be possible refer to some standard table to tell what a particular valve is designed for, unless you look at the name plate or the details (like class) embossed on the body of the valve.

Moreover, manufacturers’ range is often limited. Manufacturer A might be catering to clients who mostly use lower class valves; so that he can give a really economical product for his clients. While a more sophisticated and high profile manufacturer might target the high end customers requiring higher pressure rated valves. Yet when customers ask for a lower rated valve, he will offer them the next higher rated (designed) valve with minimum modifications to suit the lower requirements. This is more common in the case of small valves.

Ram,
Thanks for your contributions to the useful information presented in this thread. Actually, I learned some as it's been a long time since I had been intimate with valve specifications. Anyway, I got a bit of an education, and for that I say, "Thank you". Hopefully others have learned as well.

Thanks for the efforts shown by everybody.I want to add some more info regarding this.

There is a corrosion allowance in SS 304/304L also (as per spec written by PME).
Other conditions are same .
You said that there is flange rating & not valve rating. For RF type I am agree but not with SW . Pl. explain further.
However complete description is :
800 SW – 316/316L SS body, 316 SS Trim , HF , ST , HW.
300 RF - 316/316L SS body, 316 SS Trim , HF , ST , HW.

Regards
pme

Pl. continue the topic as point is still not clear.
Thanks for everybody.