WPS for turbine blades rebuild

Date 10-12-2006 19:35

First you should see what the code of construction says. Unless there is something specific about this type of repair, a butt weld coupon that covers the essential variables (primarily base metal thickness) is acceptable.

(Note - the assumption is that the build up is not a hardfacing or corrosion resistant overlay.)

See QW--202.3 in Section IX.

Charles

By Lawrence (*****)

Date 10-12-2006 19:49 Edited 10-12-2006 19:53

I can't answer your question directly.

But would like to suggest you consider Jettisoning Section 9 if possible and employing a more applicable code.

AWS D17.1 would be the specification of choice for blade tip repair. (which often do employ tungsten rich wear resistant alloys)

On the other hand, Maybe these are not aerospace turbine blades? Wheather they are or aren't I would think the manufacturer would have some recommendations on repair. Does the Manufacturer recommend/require Section 9?

To qualify procedures per D17 you have some flexability.

"4.4.3 Method of Procedure Qualification. Welding
procedure qualification may be accomplished in accordance
with the requirements of AWS B2.1 as deemed applicable
by the Engineering Authority."

"4.4.4 Alternate Methods of Procedure Qualification.
In lieu of 4.4.3, welding procedure qualification may be
accomplished by welding at least one procedure qualification
test weldment consisting of any of the following:
(1) A simulated weld joint sample.
(2) An actual part.
(3) An applicable qualification test weld.
(4) A special test weldment.
(a) Simulated service test weldment.
(b) Prototype structural special test weldments.
(c) Nonloaded special test weldments.
The Engineering Authority shall provide the test methods
and acceptance criteria for the test weldments to be used
when qualifying weld procedures."

Something to think about.

By n4v4rr0 (*)

Date 10-13-2006 16:37

thanks for you reply.
the blades are form a power plant generator and the owner only ask us for a WPS for blades repair with no mention of code or specification and we consider ASME IX most appropiate.

By jon20013 (*****)

Date 10-13-2006 17:28

in a power plant, there had to be a constructing code. ASME IX is the qualification code for WPS as you already stated. So, if it is a conventional power plant, perhaps ASME B31.1 applies, if nuclear, ASME Section III would apply. Section IX only talks about qualifying the welding procedure and the welder, it says nothing about quality requirements for the work. Surely you must have some quality acceptance criteria stated for the work of turbine blade build up welds???

By vonash

Date 01-15-2007 23:00

Yes, ASME is the proper code for this application. TIG is the preferred process.

By Bill M

Date 02-06-2007 19:16

While I am not disagreeing that ASME is the appropriate welding procedure / performance qualification code...I do not think that a steam turbine is an ASME coded pressure vessel.

By js55

Date 02-06-2007 19:30

I would have to agree that I do not believe ASME is the place for turbine blade welding quals. The construction of and repair of these units, it seems to me is entirely within the specs of the OEM involved. I don't remember 31.1 even addressing this issue.

By andy

Date 02-07-2007 09:54

I've had a little experience with reviewing weld procedures for turbine blade repairs in the UK. Generally speaking, most organisations will support the build up with a weld procedure based on ASME IX and a groove (butt) weld of an appropriate thickness. It is important to ensure that if the blade materials require heat treatment that adequate mechanical properties are demonstrated in some way and a butt weld procedure qualification is the only way to do this adequately.

Interestingly, an EPRI document on the repair of steam turbine blading does not give any advice on appropriate qualification. OEM's very often don't like to encourage repairs as they like to sell new blades....

If the repairs involve tenon build ups or other more complex geometries, then it makes sense to carry out a representative test piece to ensure fusion, lack of defects, profile etc. The killers to steam turbine blades are cracks, linear indications, unfused areas where chemical hide out can occur so the best acceptance criteria is no defects.

You should check with the equipment owner what the acceptance criteria is and that they are happy to accept qualification based on an ASME IX butt weld.

Hope this is useful...

By js55

Date 02-07-2007 14:51

Thanks Andy. I believe you've cleared the issue. ASME IX can be used as a 'framework' so to speak, providing a method by which welding variables are being addressed, but additional testing more specific to this application is required to convince of the welds viability. Its interesting, 31.1 is not going to address this issue simply because it is beyond their scope, ASME IX probably has never even considered expanding their scope to this field, EPRI probably won't since they usually, to my knowledge don't deal with qualification issues at all. And as you say, the OEM's are reluctant for commercial reasons. Talk about caught between a rock and a hard place. It all comes down to what the owner will accept.

By js55

Date 02-07-2007 14:57

Andy-Let me ask this: given that ASME IX is concerned only with tensiles, bends, and impacts, and that turbine blade service, I would assume has little concern for toughness or ductility wouldn't it be necessary to supplement ASME IX quals significantly? Tensiles can be related, to a certain extent, to hardness and creep, but ductility and toughness it seems to me would have little value for that service. I mean, if a test failed ASME IX bends (20% outer fiber elongation) would that be significant for blade service?

By andy

Date 02-07-2007 15:51

js44 -

Good question. Let me first say that in my experience it is notoriously difficult to get hold of records of PQR's from OEMs. Having said that, I just looked and I found three in my files, all of which (9.5 mm thick) were bent to 180 and were satisfactory. In addition to these tensiles, hardness, macros and charpies were carried out. They were on fairly standard 12Cr materials though, which is the main material I'm familiar with.

The performance in a bend test may depend on the material, but will be an indicator along with hardness and tensiles of the correct tempering of the weld and HAZ, thereby indicating ductility. One of the functions of the bend test is to expose defects and inadequate ductile material. If a bend test failed before 180 was reached, I'd be looking to see what caused the failure - but it wouldn't necessarily be detrimental to service.

Ductility is an important factor to prevent defect growth in service, but one would hope that the appropriate NDT technique could find defects that were not acceptable fbefore entering service. Incidentally, there are other factors to consider - inadequate tempering may lead to microstructures that are hard and susceptible to stress corrosion cracking in service and this should be detected by the hardness test. Some blade materials are susceptible to temper embittlement - this is not detected by hardness but will be by impact testing.

Hope it helps...

By js55

Date 02-07-2007 18:44

Thanks Andy-Great clarification. SCC and temper embrittlemnt hadn't occured to me. This one's gettin printed before it goes into archive oblivion. And I believe you on the troubles with OEM's. They sorta exist in a world of their own.

By ssbn727 (*****)

Date 02-07-2007 21:14

Hello again Js55!

I've got some more articles here in .pdf format with respect to turbine blade repairs.
I hope you find them useful.

Respectfully,
Henry

Attachment: Repairweldingturbineblades.pdf (798k)

By ssbn727 (*****)

Date 02-07-2007 21:22

Here's another one, and I have a few more that I've got to look for but when I locate them, I'll post them as attachments also.

Respectfully,
Henry

Attachment: Siemensweldtubinerotors.pdf (702k)

By ssbn727 (*****)

Date 02-07-2007 21:32

Here are some more.

Respectfully,
Henry

Attachment: R2-381-030901.pdf (105k)

Attachment: r265a.pdf (313k)

Attachment: ps285.pdf (467k)

By js55

Date 02-08-2007 15:11

Just what I need Henry. More info to cloud my head. Just kiddin. I appreciate it. You just never reach a point where you seem to know enough. The turbine stuff is not something I have been involved in but there are principles there that can be applied to many other applications.

By andy

Date 02-09-2007 08:49

RExcellent papers - hope you don't mind but I've grabbed them too. Rotor repairs are something else. I've not been invoved in one (yet) but do know that facture toughness is a very important property in these types of repairs considering the materials in use.

Thanks for these!

Andy