Flow nozzle in B31.1 steam piping 2

[tamal1475]

Is it necessary that the flow nozzles that are butt welded to steam piping made to ASME B 31.1, need to have code stamp? Basically it is a pipe with a conical contoured nozzle welded inside the bore to control the flow of steam. Both ends of the pipe is butt welded to steam pipes to put it directly on the steam line. Flow nozzles are a bought out item for piping fabricators and the suppliers are normally not ASME stamp holders. The Flow nozzle certification contains the necessary pipe material details that are required by the piping fabricators for welding them to the main steam pipes.

 

[davefitz]

The pipe section must meet B31.1 par 102.2.2 and all required material certs must be forwarded. This implies the pipe section itself must be selected from B31.1 appendix A and the welding preheat and PWHT must meet the B31.1 requirements using code certified welders. Although the weld is not a pressure containment weld, if improperly welded then the weld zone might not meet assumed code material strength values. For example , if the PWHT over-tempers the weld then it would be a weaker than the designer assumed, and if that pipe section is exposed to a strong axial tensile load then it may eventually fail. It is not clear how you can document that those requirements are met if you do not have a code stamp.

Recent failures with flow nozzles are associated with using a stainless nozzle inside a P91 pipe. Don't do it. For HP main steam pipes, a flow nozzle is not strictly needed- you can use a short radius elbow with an "elbow tap" as indicative of steam flow rate, after it is calibrated.

"Whom the gods would destroy, they first make mad "

 

[Duwe6]

Think of the nozzle as a 'structural attachment' and follow the ASME rules for that. This includes a qualified WPS for that particular material combination. P8 stainless on P91 9-chrome sounds pretty stupid to me, not supprised that it failed. Their problem may have been as simple as differential material thermal expansion. That s/s nozz was only the right size to fit properly at whatever temperature the pipe was at when the root was welded. At any other temperature, there would have been a LOT of differential stress. So in addition to compatable materials, make some allowances for differential expansion.

Makes an SR ell with an O'let tap sound pretty good, doesn't it?

 

[hacksaw]

"it is a pipe with a conical contoured nozzle welded inside the bore to control the flow of steam. Both ends of the pipe is butt welded to steam pipes to put it directly on the steam line. Flow nozzles are a bought out item for piping fabricators and the suppliers are normally not ASME stamp holders. The Flow nozzle certification contains the necessary pipe material details that are required by the piping fabricators for welding them to the main steam pipes."

If you need a HP steam meter purchase one from an established supplier. You have greatly under-estimated what is involved. It comes with welded plates on each end for shipping.

With flow nozzles, you are better off purchasing it with a meter tube to match the piping spec, then all you have to do is install it.

Elbow taps in HP steam? Don't waste your time.

 

[davefitz]

Elbow taps in HP main steam lines have been successfully used on combined cycle power plants for over a decade, in the case where there are multiple reheat type HRSG's feeding one common STG. In those cases the reheater steam flow must be pro-rated to each HRSG based on each HRSG's specific HP main steam flowrate, so the flow indication from each elbow tap is primarily for control purposes and not for metering costs to a cogeneration steam client. The flow indication is used to pro-rate the reheater flows and also as part of the 3-element HP drum feedwater flow element controller.

The elbow tap is calibrated during initial commissioning by isolating the HP drum blowdown and comparing the steady state feedwater flow indication ( from a calibrated flow nozzle at the DA or BFP discharge)to the T+P compensated DP across the elbow tap. It is certainly as accurate as the classical use of STG first stage pressure as historically used on 1:1 rankine cycle plants.

"Whom the gods would destroy, they first make mad "

 

[hacksaw]

we agree that they are not used for metering where the actual flow is needed.