Steam Supply/Return Sizing Codes/Standards

[KANN]

For large generating stations, do specific codes and standards govern the steam pipe sizing? What about low & high pressure return piping size, and the location/configuration of drips?

Is the sizing accomplished by power plant design engineers based on steam industry guidelines/best practice and experience? Does EPRI, IEEE, or others publish such guidelines?

Are specific computer sizing programs used?

I am primarily interested in saturated steam flow conditions where the steam is not dry.

 

[athomas236]

Try EPRI report NP-3944 dated April 1985 called Erosion/corrosion in nuclear plant steam piping and inspection programme and guidelines

 

[KANN]

The EPRI report sounds interesting, and may be helpful, but EPRI wants $10,000 for a copy of the report. Furthermore, I understand where the report is available, it is for internal use only, and I am not in the power industry. Since my interest is in personal professional development, neither option is accessible to me. Are there any other sources that would get at my questions?

 

[athomas236]

send me your email address and I will send details requested
ahtomas236

 

[KANN]

My email address is knislyna@fosdickandhilmer.com.

Thanks, Ken

 

[MJCronin]

KANN,

Try Crane Technical paper #410....(Flow of fluids through valves, fittings, and pipe, Technical Paper No. 410, 1985, Crane Co.)

See:

http://www.cranevalve.com/tech.htm

This old, but useful reference contains design formulas and velocity limits for saturated and superheated steam systems. As I recall, piping should be sized for saturated steam system velocities in the range of 6000 to 10,000 fpm.

Look at the FAQs under the "Piping & fluid mechanics" forum...... A helpful, well respected engineer has written some interesting information there

As an alumni of "Stone & Webster" engineering, I can tell you that the Main Steam and hot-reheat systems of a power plant required a special "present value" economical analysis of line size.

Because the pressure drop in these lines was worth so much over the lifetime of the plant, extra cost was typically justified in the specification of larger line sizes.

Good luck...... Let us know how you make out

MJC

 

[KANN]

MJCronin -

My question is not how does one go about sizing steam piping. I do that routinely and TP410 is a valued resource.

My question is perhaps more clearly: what parameters do power plant designers use to select the size of the steam pipe?

TP410 helps size pipe based on velocity and pressure drop. But what velocity governs the selection and for what reason? Is velocity limited to control erosion - if so, what are the guidelines. Responder ahtomas236 has addressed erosion/corrosion. Are there some general guidelines for limiting velocity to control erosion without regard to corrosion? Will 12,000 fpm prevent significant erosion over the course of 20 years, 30 years at full time service?

What about limiting velocity in concert with condenstate flow. Are the often used steam piping guidelines of: 1"/40' with cocurrent flow, 1"/20 feet for countercurrent flow, drip spacing every 300 to 500 ft and at changes in elevation, etc. - what governs the saturated steam piping design in power plants too, or are there more stringent guidelines in use?

Is the piping sized strictly on a life-cycle analysis basis including all the above in a specialized program developed by specific firms that design/build Power Plants?

Hope this makes my initial inquiry more clear. Thanks for your input, I see you have a backgound in the power industry, so maybe you know first hand how some of the decisions I discuss are made.

 

[poetix99]

As MJCronin (could he be the very same "helpful, well-respected engineer"?) said in his last post, one of the most important considerations for large generating stations is not erosion, but the incremental amount of electric power available with a larger pipe. Lower velocities giving smaller pressure drop, giving more available energy at the turbine, giving more power from the generator.

The weight given to different factors can vary from application to application. I doubt, for example, that erosion is a great concern in the inlet and reheat piping of a 3000 psig 1100F/1050F/1050F power plant. Nuclear applications have less superheat, if any at all, in which case erosion (obviously) must be given careful consideration. Relatively small (<50MW) co-gen and mechanical drive applications are another thing altogether.

It is always appropriate to look at it from a life cycle consideration, but the criteria might vary.

Mr. Cronin will, I hope, repost.

 

[steve58]

KANN,

A lot of good advice in the previous responses. One additional issue to consider, which you raised in your original question, is the location/configuration of drips or drains. This will be a key issue for any piping that has the potential for water induction into the steam turbine (main steam, reheat and extraction piping). Add this design concern to your list of concerns when designing such piping systems. The ASME has published a very good document regarding Water Induction Protection for Steam Turbines. I'd recommend you get a copy if you are getting into designing these critical piping systems.

 

[KANN]

steve58 -

Thanks for the reference to the ASME publication, TDP-1-1998, &quot;Recommended Practices for the Prevention of Water Damage to Steam Turbines Used for Electric Power Generation&quot;. I have not seen that RP and will obtain a copy and review it.

So, how do you determine the location/cofiguration of drips and drains? What guidelines do you refer to, for example for slope and frequency of drip placement? What about the condition of counter-current steam-condensate flow?

 

[steve58]

KANN,

In general, the location of the drips/drains on high energy piping systems will be determined by the physical layout of the piping system. Superheated steam will not generally require condensate drainage during steady-state operation, however, the transient states (such as start-up from cold condition or cooling following a shutdown) will generate condensate that must be drained in order to prevent water induction into the steam turbine and/or water hammer damage to the piping systems. The rule of thumb for steam piping is a slope in the range of 1&quot;/20' to 1'/10' to ensure proper drainage to low points. Typically, any horizontial leg of the piping system should have a drain at the low point. Remember to look at both hot and cold positions of piping to ensure drains are truly in the low points. Moreover, all valve locations will require drains, some of which should be automated if they are cycled during shutdowns and start-ups. In particular, turbine stop valves will have before-seat and after-seat drains to ensure adequate drainage. Extraction and reheat valves will also have drains. There should also be drains downstream of desuperheaters. Typically, these drains are all directed where possible to the condenser to preserve the condensate.

You should get some very specific details/recommendations on both locations and drip system configurations (including instrumentation and control requirements) from the ASME Water Induction guidelines. You may also want to check out a copy of Piping Handbook by Crocker & King - there is a chapter devoted to piping systems for Steam Power Plant Piping.

Hope this helps.

 

[KANN]

steve58 -

Thank you again. I regularly use the Piping Handbook (now 6th ed. by Nayyar). From your reference to that text, may I infer that the approach to the design of drip and drain locations in large power generating plants are determined in much the same manner as in steam systems in general, except for special considerations prior to turbines (TDP-1).

If my inference is correct, then part of my original question is answered: the design is based on common steam piping industry standards and experience, it is not set forth in power industry standards, again except for special locations/conditions such as turbines.

I will want to review TDP-1 first, before asking any further questions.

 

[KANN]

steve58,

I have obtained and reviewed a copy of TDP-1. In terms of the issues I raised, the recommended practice only addresses drip locations at valves and in other equipment specific locations, and recommends slopes for the steam seal and gland condenser piping.

Unfortunately it does not address the slope of piping in general, maximum spacing of driplegs, nor the steam velocity under cocurrent or countercurrent flows.

If you find recommendations which specifically address these issues, please let me know.