[MW:1038] Re: extended bonnet valves for high temperature service

dear syam, Reformer tubes it self they are using alloy steel tubes.incol in not a manditory for this temperature. thanks satya On Thu, 14 Aug 2008 Shyam Herur wrote : >Thanks for the reply and the inputs.Regarding the valve material, if such >high temperatures do exist in the steam list we are likely to change it to >Inconel600 or better. > >Shyam > >On Mon, Aug 11, 2008 at 2:19 PM, <kannan.sundaram@linde-le.com> wrote: > > > > > Though such high temp valves do exist, but few in the plants and are > > specialized construction, due to the temp/press and service and the location > > of the valve and safety requirements. > > > > The extended bonnet construction is one option to dissipate heat and to > > lower the heat at the stem packing similar to the reduction of cryogenic > > valve temp propagation to the stem packing and to avoid subsequent failure > > of the packing and operation of the valve. In all, the subject of concern is > > the stem packing failure. Other options are finned bonnet constr, stem > > packing with separate cooling system. > > > > Protection for valve handwheel operation is not a major concern as it can > > be chosen as Motor/Pneumatic operated valve. Most of the hand operated > > valves requires once in a year operation in such high temp service. > > > > Coming to the stem packing, > > 1)The usual ones are in one or more combination of graphite, metal rings, > > Elastomer rings, Lip seals, simple TEFLON rings etc. > > 2) In the moderately higher temp. range, only Graphite+alloy is used in > > diff. arrangements. > > 3) For very high temp such as your case, cooling system or the extended > > bonnets and same as 2) packings are used. Also many new proprietary packing > > arrangements are available in the market. Evaluating them is an important > > part of a material engineer's role. > > > > Additional one to be noted is, the valve basic design is also to be > > reviewed. Process engr. is not a valve specialist. So the material engineer > > is supposed to evaluate such cases. In this case a rising stem valve type > > design to be avoided as it has vertical and rotation wearing on the packing. > > For controlling a butterfly valve could be evaluated. For Gate types, a > > knife gate valve could be thought of. Pl. take note that such evaluation > > has many things to be accounted for such as leakage allowance, emission, > > hazops, ATEX concerns, operation difficulty, trim erosion and not the least > > process parameters like pressure drops, zigma allowance, opening/closing > > period, service fluid etc. > > > > Coming to your question, > > 1) Parameters controlling the bonnet height ...depends on the stem packing > > design and heat propagation to the packing. As a thumb rule for alloy > > constr. 250mm shall be the min. height. > > 2) On tests....apart from the usual tests, service condition test is > > required to be performed. But if the manufacturer has a prototype test > > certificate, it could be accepted. Again it depends on the application of > > the valve. In your case prototype should be OK, in my opinion. > > 3) Create these valves as special parts and specify the individual > > condition of operation and design to ensure correct valve/packing design is > > offered by manuf. > > > > ***** > > Important note is the temp you specified and the valve material specified > > does not go well together. Being a HP steam and at 700 deg. c(which itself > > is very unusual), SS is no good and it has to high alloy grade. Or your > > design condition is to be verified. B16.34 defined the temp. limits in the > > notes of every rating table. > > ***** > > > > Regards, > > Kannan. > > > > > > > > *"Herur Satyanarayana Shyam \(External\)" < > > SatyanarayanaShyam.Herur.Guest@snamprogetti.eni.it>* > > Sent by: piping_valves@yahoogroups.com > > > > 11/08/2008 10:03 Please respond to > > piping_valves@yahoogroups.com > > > > To > > <materials-welding@googlegroups.com> cc > > <piping_valves@yahoogroups.com> Subject > > [piping_valves] extended bonnet valves for high temperature service > > > > > > > > > > Dear friends > > > > I have a query related to valves used at very high temperature for the > > refinery in Russia Im working on. The service are high temperature > > hydrocarbon, process with hydrogen or hot air and high pressure steam with > > ratings of 300# and 2500#. Design temperatures(stream list not yet issued by > > process) in FEED contractor piping class are 700 to 750 degC. Valve > > material(CF8, C>0.04)The FEED contactor has put a note against the > > valves(gate and globe) in his pipng class ' *valves shall be supplied with > > extended bonnet and heat dissipating elements to obtain a packing > > temperature of 450degC maximum*'. We have come across extended bonnet > > valves for cryogenic service.I would like to know if members have experience > > with extended bonnet valves for high temperature service. What are the > > parametres to be considered by the vendor in deciding the height of the > > bonnet? What are the tests/set up to be performed by the vendor to > > demonstrate that temperature at packing is <450°C.Is it feasible to have a > > extroordinarily long bonnet in order to maintain T<=450 deg C?? What are > > the other packing materials other than graphite that can be used to > > compensate for the height of the bonnet. line gaskets are spiral wound with > > SS304H windings and mica/graphite filler. Regards & Shyam

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