Main Steam Piping Material 2

[kb44]

I am replacing a main steam 45 due to soft spots and am wondering what the difference is between ASTM A335 Gr. P91 and ASTM A234 WP91. I think the A335 is extruded pipe while A234 is a fabricated elbow. This is a 3D fitting. Which material reference is appropriate?

 

[vesselfab]

look in astm / asme material

anything with a-234 is a fitting

a-335 is hot finished or cold drawn pipe

 

[metengr]

kb44;
SA 335 is a seamless pipe specification. SA 234 is a specification for the manufacture of fittings. The appropriate specification is SA 234 and you should specify seamless WP91 material. Read this specification, SA 234 carefully, and invoke the necessary Supplemental requirements,S1,S4, S5 and S8.

 

[MJCronin]

banu...

"Soft spots"..??? on an Main Steam system elbow..??!!!

My only experence with soft spots has been at the top of my son's head when he was an infant.
(

http://pediatrics.about.com/od/yourbabyweekbyweek/ss/baby_wk_svnteen_4.htm)

Can you explain ?? By what industry accepted criteria do you determine a piping "soft spot"..??? Does this only apply to your P91 piping systems...???

How about that 3D fitting.....I am not sure what you mean by that term ??

I agree with the comments of "vesselfab" and "metengr"..

-MJC

 

[MachinaMan]

Hi kb44,

Be extremely carefull with your PWHT tempearture profile for 91 material. They must be dead on.

Hi MJ,

I think he/she means the radius of the elbow is 3x the diameter of the pipe.

 

[vpl]

hmmm, main steam line elbow. Sounds like your soft spots are really flow induced corrosion.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[pennpiper]

Good thought "vpl"

I have also seen "de-lamination (of the pipe wall) in P91 material.

 

[stanweld]

Soft locations in A-335 P91 pipe and A234 WP91 fittings occur due to improperly controlled or performed normalizing and tempering heat treatments, preheating and PWHT. From my experience soft locations on fittings typically occur along one of the neutral axis. The whole fitting may also be soft due to annealing (controlled slow furnace cooling) rather than normalizing (air quench). We have seen soft spots along fabricated pipe spools where overheating occured during PWHT, and hard spots in welds of furnace PWHT'd spools attributed to localized low temp zones. The list is endless. Proper, effective controls are required and adequate testing to verify same.

 

[metengr]

There is no FAC in Grade 91 pipe material. Absolutely concur with Stanweld.

 

[MJCronin]

General question....

I know that this has been brought up in other threads in this forum, but....

Doesn't anyone have a sense that there may be a subtantial risk out there where some owners of relatively new, high-temperature, high-pressure steam systems (this is P91 material) are "replacing elbows"..?!!????

There are plenty of P11/P22 piping systems out there that have been operating for 40 years.... yes, some have failed....but we are not replacing them as common sense would dictate.

Why ??

 

[stanweld]

MJCronin:
Many companies do know and have or are actively investigating their P91 installations. EPRI is actively investigating the problem as well. We will no doubt supply EPRI with suspect P91 pipe spools removed form operating plants due to low hardness/ferritic microstructures. There have been a number of reports in major User publications devoted to the P91 problems. Yet the problems persist!

 

[metengr]

There are plenty of P11/P22 piping systems out there that have been operating for 40 years.... yes, some have failed....but we are not replacing them as common sense would dictate.

Why ??

Because those piping systems that are seam welded undergo TOFD examinations looking for creep damage either along the fusion zone or adjacent to it. Some have decided to conduct wholesale replacements of seam welded piping systems to avoid having to conduct periodic volumetric examinations.

For seam less piping systems, the only problem would be girth welds and this is manageable through periodic volumetric and surface examination of girth welds. Regarding Grade 91 material - poor heat treatment results in unpredictable creep behavior.