PH13-8Mo; Afraid fo Bend Tests!!! 4

[tc7]

Several years ago, we attempted a PQR on 13-8PH (or PH 13-8MO) and tensiles and bends failed miserably. The project was cancelled until now.

The history, as far as I can tell was that the original procedure called for:
Mat'l: PH13-8Mo Condition A
Process: GTAW
Filler: 1/16" PH13-8Mo
Joint Types: plate, V-groove, flat & vert
Preheat: 250F
Interpass: 550F
Shield Gas: Ar(20 CFH)/He(5 CFH)
Volts: 200
Amps: 24-28
PWHT: Solution H/T & Precip Age to H1050 (Method AMS 2759/3)

For the upcoming PQR my choices will be to use a ER630 filler; no preheat and watch interpass at 300F max; same PWHT. Other than that, I will turn down the amperage a litle bit.

Any other suggestions to improve success with my bend tests?
I am afraid that the condition H1050 is so hard that it will fail bends even if I do a perfect procedure. (bend tests IAW AWS methods)

Suggestions please.
Thankyou

 

[TVP]

You may be correct regarding difficulty passing a bend test with PH13-8Mo in the H1050 condition. Do you know what the strain will be when bending your specific parts? It should be easily to calculate based on the thickness, etc. Do you know what the problem was regarding tensile tests on the previous weld setup? Was it achieving the desired ultimate strength? Elongation? Both?

 

[tc7]

TVP-
Tensiles were 168ksi actual vs. 175ksi reqd.
Elongation was 11% vs. 12% reqd.

I don't know how bend tests were judged, but they were all reported as UNSAT; each of two Face bends and two Root bends were bent through 180 degrees and pin diameter was 1.834-inches.

I don't know how to answer your question on what the bending strain was. I should have mentioned the previous test plates were 1/4-inch thick, i may be using 3/8-inch thick.

Does this help?
Thankyou

 

[metengr]

If the bend tests were performed in accordance with the requirements in ASME B&PV Code, Section IX, the bend testing results in a 20% outer fiber strain. You can easily measure this by using scribe marks placed on the tension side of the bend sample and measure the distance before and after bend testing.

It looks to me that your proposed revised welding details seem reasonable. The shielding gas for GTAW should be helium. The H1050 should pass a Section IX bend test.

 

[metengr]

I forgot to mention that for materials that have less than 20% elongation by material specification, you can adjust the diameter of the mandrel or jig to compensate for less then 20% elongation using Section IX guidelines (I don't know about other welding standards).

I believe for the 13-8 PH in the H1050 condition, the minimum specified elongation is 12%. So, you will need to adjust the mandrel bend radius for this specific case to at least provide a minimum fiber outer strain of 12%.

Here is the equation;

outer fiber elongation percent = 100*t/A+t

where A = diameter of the bend mandrel
t= thickness of the bend sample

 

[tc7]

Hello again Met-
So based on your formula, the bend mandrel should have been (for 1/4-inch thk):

12 = (100 x .25)/(A + .25)

Yielding a diameter of 1.528-inches?

If my arithmetic is right then this diam is much smaller than the actual test mandrel diameter of 1.834-inches and I may be in worse shape than I previously thought!

Am I applying your formula correctly? What is the reference for this formula?
Thankyou.

 

[israelkk]

tc7

Check you calculations!!

12 = (100 x .25)/(A + .25) yields a diameter of:

A=1.833 inch

 

[tc7]

Right.....so a mandrel with an area of 1.833 sq inches gives a diameter of 1.528-inches, like I said.


OH! gosh, so the "A" is just a variable for diameter, not area. Got it!!!!!Glad I asked.

Thanks

 

[EdStainless]

I am a little worried about your mechanicals. You should have made the UTS and elongation without much trouble. If you don't make elong, then don't bother bending them.
Why the move to 630 filler? Will it give you better elong?

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[TVP]

I agree with EdStainless-- don't bother bend testing anything that does not pass the tensile test. I wonder why the strength was not at least 175 ksi? Did the parts fail in the weld or HAZ? I would suspect inadequate solution treatment if both elongation and tensile strength were low.

 

[tc7]

Hi Ed-
There were a couple of reasons why I wanted to use 630 next time around: I have it left over from a recent 17/4 project which got cancelled AND we can find only one supplier of 13-8Mo wire, but they are the same one used previously (I have doubts about the quality of the rod from this previous supplier). Additionally, the 630 filler is a certified AWS rod and I think the 13-8Mo is not.

The elongation of the (unwelded**) 630 is similar to the Ph 13-8Mo and may even give me a slight advantage. However, now I am seeing that the unwelded** UTS of 630 at the H1050 condition that I need is about 150ksi, quite a bit lower than I was looking for. I didn't realize this stuff is SOOOOOO extremely sensitive to slight difference in post weld conditioning.

** By "unwelded" I am referring to the 630 material properties in a H1050 condition before it gets melted and mixed with the 13/8 base metal. IS THERE ANY WAY TO CALCULATE & PREDICT THE COMPOSITION OF 630/13-8 WELD MIXTURE? THEN PREDICT UTS & ELONG? that is probably a silly question.


Thankyou.

 

[tc7]

TVP-

My files don't show if the previous failure was in the weld or in the HAZ and that is a key question, isn't it!! The technical folks involved at the time are no longer available.

But let me ask this - for a PH material, will a HAZ still exist after a proper solution anneal and precipitation aging?

I appreciate your interest.
Thanks TVP.

 

[EdStainless]

Predict aging response and properties of a mixture of two different PH grades? If I could do that I wouldn't be working a day job!
We see reliable variation in properties with 17-7 between 1000, 1025 and 1050 age temps. Yes, they are sensitive.

HAZ, well my thought is that while you won't have the hardness variations after anneal and age you will still have grain size differences and you may have an aging response difference. You may need to run some trials with different anneal hold times and temps, as well as some slight variation in the aging temp and time.

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Rust never sleeps
Neither should your protection

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[tc7]

CALLING ON METENGR!!!!
If you are still checking on this thread, can you please advise on why you earlier recommended using helium for this weld? I presume you are indicating 100% helium? I am wondering what advantage on He only?

Also what would you think about an Inconel welding rod for this 13/8 weld? Any possibility? Thankyou, I appreciate your opinions.

 

[metengr]

tc7;
See the information below from AL;

http://www.alleghenyludlum.com/ludlum/pages/products/xq/asp/P.155/qx/product.html

From a weldability standpoint, Inconel can be used. However, you will not achieve the desired UTS or YS using Inconel filler metal. See below for more information;

http://www.hightempmetals.com/techdata/hitemp13-8MOdata.php

 

[EdStainless]

Ditto those last comments. Considering that these alloys can be difficult to weld (Al and Ti don't help) using He will be a good idea. You could use some Ar (25%), but why bother.

There are a lot fillers that would be weldable, but make strength you will need to use a PH grade.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[tc7]

Thankyou Met & Ed,
I will post results (good or bad!) to let you know how I made out.
VR,
tc7