Stream turbin's blade repair

Date 01-20-2006 13:42

Best to use a matching filler wire, ER410.

You will need to preheat, between 100C and 200C. For thin sections, associated with erosion 100 is probably enough. Limit interpass temperature to 200 C.

Following welding, slow cool under insulation to room temperature, then temper between 680 and 740C. Towards the top end you will get better toughness in the HAZ and a lower hardness.

This blade may distort. Keep heat input low throughout welding.

Hope this is useful

http://www.suppliersonline.com/propertypages/410.asp#General

Andy

By - Date 01-20-2006 14:43

Andy, good information, but may I respectfully add just a little?
Actually, the preheat temperature of the martinsitic stainless steels should be determined by the carbon content of the steel. 410 has a maximum carbon content of 0.15%. For martinsitic steels with a carbon content of 0.05-0.15%, the preheat should be a minimum of 400F (204C). The ASME Boiler and Pressure Vessel Code recommends a minimum preheat of 400F for those materials listed as P-6 in Section IX. The martinsitic transformation temperature ranges and air hardening characteristics of these steels are sufficiently high that preheating at 600F and below has minimal effect on the hardness of the HAZ or weld metal. A recommended technique is to use a high preheat (400F min.) and interpass temperature (also 400F) and very slowly, as Andy said, cool through the martinsite transformation temperature range to about 200-250F and then directly go to the tempering.
Andy, I respectfully wanted to clarify the minimum preheat temperature recommendations for a 410. You are right, though, that distortion will have to be carefully monitored, but that is the nature of the beast if using a martinsitic stainless steel. The recommended preheat, interpass temperature, and PWHT requirements are what they are for achieving maximum properties. Thank you.

By andy

Date 01-25-2006 09:20

Good call Chuck - I stand corrected. You are of course correct in your information. I've been moving desks so its taken some time to respond.

EPRI have an excellent publication on steam turbine blade repairs (TR-107021) which gives information on repairs to these components. Of course, the organization has to be a contributor to EPRI to get this info.

For the record, they recommend preheat of 500 - 600 F (260 - 316 C) but add a footnnote thatfor joints in thin materials (<1/2") some fabrictars have found it possible to weld materials of this type having lower carbon content and low hydrogen consumables using a pre and interpass temp of approximately room temp followed by an intermediate PWHT at 1300 - 1400F.

Recommended PWHT from EPRI is 1300 -1400F (700 - 760C).

Preheat for these materials according to some consumable manufacturers and papers can be 150 - 250C, but I recognise that the lower value depends very much on factors such as low restraint, low hdrogen etc. This highlights the need for proper procedure qualification and evaluation.

Thanks for your correction and additonal information!#
Andy

By radarlitz Date 01-20-2006 19:09

I'm no mechanical engineer - but I've been around power plant steam turbines for 32 years .... and I've never seen any welding perfomed on diaphragms, nozles, disks or other rotating parts. We'll grind out small cracks, dings, and impact marks. Otherwise - excessive damage or wear or large cracks on blades, nozles, or diaphragms are replaced with new parts parts as needed. The "no weld" policy may be with a particular brand of turbine though. Check with your turbine manufacturer or turbine repair specialist to see what they recomend.

By jon20013 (*****)

Date 01-20-2006 19:14

Repair of turbine blades has become big business and there's now several companies focusing in on the " how to do it right." Having never done it myself all I know about it is it can be very tricky and wouldn't even venture a guess at suggesting a "how to." Good luck!

By Lawrence (*****)

Date 01-20-2006 19:36

There are a whole lot of factors that go into blade repair procedures.

Too many to state in a forum.

However, inventing your own procedure may not be necessary. As Jon stated above, this has been done before, with both manual and automated welding/finish machine operations.

Often blade tips are restored with a close match parent alloy filler and then "capped" with a more wear resistant alloy that might include cobalt or tungsten, Haynes 25 (L605/AMS 5796) is one example.

You will need to consider; filler, stress relieve, fixture, distortion, heatsinks, pre/finish machining and inspection to tackle your job.

These folks are the best consultants I know when it comes to stuff like this.

Precision Welding Technologies http://www.pwt-online.com/