GE Material Specification

[SuperLectric]

Hi All,

First post here. These forums have been very helpful for a young engineer.

Is there an equivalent ASTM specification to GE's B4A39 pipe specification?

The B4A39 designation was listed on the BOM for a 1960s vintage Turbine.

We are planning to make a welded connection to this line and I want to make sure I know what we'll be welding to.

The line is designed for 950 F at relatively low pressure (<150 psig).


Any help would be greatly appreciated,

Thank you.

 

[metengr]

It looks as though from my GE large turbine material applications table, the B4A39 is carbon steel pipe with a maximum carbon content of 0.30% by mass. The temperature range listed is 500 to 750 deg F, which makes sense.

For your application, this is not applicable. For 950 deg F, the material is B50A137A.

 

[SuperLectric]

Thank you for the quick response to this.

I double-checked and the design temp for this line is indeed listed as 950 F. Although you're right, that doesn't fit the temperature range from your manual...

Given this discrepancy, we may use a PMI gun to verify the material.


Thank you again.

 

[metengr]

I would bet the pipe material is 1.25% Cr - 0.5% Mo (B50A137A) at this temperature.

 

[SuperLectric]

As a follow-up, the plant had the pipe tested with a PMI gun. The picture shows results they sent me from the test. The gun did not provide a match from its material library.

I could not immediately find a matching composition in the B31.1 book. I'll have to do some more research to find the matching ASTM standard.

These test results don't appear to match the composition of the 1.25 % Cr - 0.5% Mo (B50A137A) metal.

The PMI gun results were:
Ti 3.59%
Cr 0.510%
Mn 0.717%
Fe 91.83%
Cu 0.511%
Zn 2.02%
Pb 0.322%

Thoughts?

 

[metengr]

Did you carefully grind the surface to remove scale/oxide? You need a grinder and not a flapper wheel.

 

[SuperLectric]

I wasn't present for the testing, nor did I specify specific surface prep...

I was told the plant used a wire brush and sand paper to prepare the surface.

I'm just not sure where the Titanium measurement would have come from if it wasn't in the metal itself.

 

[metengr]

I was told the plant used a wire brush and sand paper to prepare the surface.

Not acceptable. The surface should be locally ground smooth to 1/8" depth to remove mill scale, oxide and other contaminants.

Do it again.

 

[SuperLectric]

We have not re-inspected the material yet.

After taking a closer look, I noticed that several flanges attached to this seal steam header pipe were stamped as made with A 181 steel. That would corroborate the GE B4A39 material specified on the BOM, even though it has a lower temp rating. Without re-inspecting, it seems like the seal steam header was made with standard carbon steels, even though the pipe's design temp is above those materials' creep range. Perhaps since this header is at such low pressure, alloy pipe was not considered, even with the high design temperatures. Or, back in the 60's when this plant was built, creep was not a factor in their design.

Those are the only explanations I can think of for this pipe with a 950 deg F design temp to be built with standard carbon pipe.

 

[SuperLectric]

Also, thank you for your time.

 

[metengr]

SuperLectric;
The seal steam header piping will operate below 950 deg F. I am thinking this could be saturated steam temperature versus main steam. Again, carbon steel will degrade and result in creep failure at 950 deg F under internal pressure. GE was very conservative in their turbine inlet piping and extraction piping designs. Check your operating temperature profiles and re-inspect.

 

[SuperLectric]

metengr,

I've based the 950 deg F temp based off the seal steam header drain temp, which is assigned a temp of 950 deg F on our GE drawing.

I would not think the seal steam header would actually operate at that high temperature, but I am confused why the drain on that line would be assigned the 950 deg F temp if they did not expect or design the seal steam header for that temperature.

Thank you for your response.

 

[metengr]

SuperLectric;
Do you have any TC's or temperature probes from operation that can substantiate your information? Have you discussed this with GE? Something is not right with your information.

 

[SuperLectric]

metengr,

I'm not sure if the plant has temperature probes on the sealing steam, I will need to verify.

We have not contacted GE yet. I would like to get a proper material analysis performed to determine the true pipe material. It is a mystery until we take either of those steps.

Thank you.