A106 Gr B versus P11

[wtflippin]

To prevent flow accelerated corrosion in HRSGs, we specify HRSG suppliers provide A106 grade B with a minimum chrome content of 0.016%. Several of the suppliers provide P11 with a chrome content over 1.0%. When the HRSG is chemically cleaned during startup, the waste is categorized as hazardous because of the higher chrome content from P11 material, resulting in expensive disposal costs.

Are there any alternatives for HRSG piping/tubing materials that would likely not result in a hazardous waste stream following chemical cleaning, but would be rated for standard power cycle temperatures and pressures and would withstand flow accelerated corrosion?

 

[metengr]

From what I have seen with EPRI documents and other information on FAC studies, approximately 0.1% addition of Cr content to carbon steel increases resistance to FAC ten fold. I have also seen Cr (equiv) formulas that indicate the combined effects of Cr, Cu and Mo w% additions must be > 0.09 to afford resistance of FAC or erosion/corrosion.

If you review the ASME SA 106 Specification for carbon steel pipe, the max %Cr is 0.4%. If you can order with the higher Cr content from a supplier even at 0.1%, this would be the best alternative. Your 0.016% Cr content is probably too low to assure long term FAC resistance. Otherwise, you can go with P11 but this would require some added precautions for welding (use of preheat and matching filler metal), and of course the issue of hazard waste material after a chemical clean of the HRSG.

For HRSG tubing, you could evaluate ASME SA 213 T2 material, which is a 0.5% Cr-0.5% Mo alloy steel. Availability may be an issue with T2 tube material.

Yes, we have had the same problem with even our supercritical power boilers that contain T11 in the upper elevations of the ww tube circuits.

 

[wtflippin]

Thanks metengr,

I misstated our specification, should have been:

For carbon steel piping that conveys single-phase water at 200-500 deg F a minimum Chromium Equivalent (CReq) (where CReq = Cr + 0.19Mo + 0.4Cu) shall be provided. The minimum value of CReq shall be equal to 0.16 %. Weld filler material shall have the same CReq as the base metal.

So, if I read your reply correctly our contractor could:
(a) specify SA 106 to his supplier > 0.16% CReq or
(b) specify SA 213 T2 material (0.5% Cr-0.5% Mo) or
(c) specify P11 with significantly higher CReq .

Economically/Environmentally speaking:
Option (a) costs contractor money for supplier to perform adequate QA/QC to ensure Cr content but results in less chem cleaning waste disposal costs (non-hazardous).
Option (b) costs contractor more money due to higher Cr content and availability as well as filler material, and may/may not result in a hazardous waste from chem cleaning.
Option (c) costs contractor more money due to material costs and hazardous waste disposal but may require less shop QA/QC for CR content.

Is this how you see it?

 

[metengr]

Yes, the lesser of the 3 evils, A). The shop QA/QC is not that expensive versus your other two options.

 

[eyec]

why are you doing a chem clean this early in the HRSG's life cycle?

have you reviewed your water chemistry process?

this may be the cheaper longterm solution.