Line blank material choice in 9Cr material specifications

[jonesey]

We have both 5Cr and 9Cr piping material specifications. ASME B16.48 (steel line blanks) only lists forged material for 5Cr, and no 9Cr material is listed. The forged material is listed i presume because forgings are less susceptible to laminations than plate material. What type of material should be chosen for 9Cr specs ? 9Cr forging, which is not listed in ASME B16.48 or should we go with 5Cr material which has less strength/corrosion resistance ?
Any input will be appreciated.

 

[pennpiper]

jonesey,
For a Disk & Donut blind, one thing you might want to ask is:
"Will this "blind" ever see the actual line operating conditions?"
Most plate blinds (Disk) are a shut down item and more of a safety item therefore does not come in contact with the commodity at the normal line pressure and temperature.
A lesser material may be acceptable here.
The ring spacer (Donut) however will see line conditions to a limited extent.
A line quality material would be required here.

 

[jnleroux]

ASME B16.48 states that blank materials shall be in accordance with ASME B16.5, Table 1A. 9 Chrome material is listed on Table 1A under A 182 Gr. F9. I would use 9 Chrome for most operating cases, but as pennpiper, would consider using another material if there would be no way that the blind could see the normal operating temperature/pressure.
John

 

[NozzleTwister]

In my experience with 9 Cr piping systems, the 9 Cr isn't chosen for the temperature-pressure requirements alone as lesser chromes would do the job.

9 Cr is selected for its superior resistance to corrosion and hydrogen embrittlement compared to 1 1/4 and 5 chrome in hydrogen rich service at elevated temperatures.

The stabilized stainless steel grades Type 321 & Type 347 are often specified as alternative materials in lieu of the 9 Cr. On many projects that I've worked on, the material is chosen based on availability, price and the delivery schedule. I've seen several systems with 9 Cr pipe and 347SS valves.

Bottom line - If you can't get 9 Cr Line Blanks, consider using 321SS or 347SS as an alternative. Be sure to get approval from your process engineer.


NozzleTwister
Houston, Texas

 

[jnleroux]

I agree, typically piping systems don't use 9 Chrome when 5 Chrome can be used. Since ASME B16.48, section 2.2.3 states that mixed material joints (including blanks) need to use the lower rating, make sure that the working pressure from B16.5 for the material is high enough for your application if you choose to use a stainless steel. Stainless steels do not always have the same allowable ratings as 9 chrome. For example, a Class 300 system designed for 800 °F will allow for up to 510 psig using 9 Chrome, while Type 321 will allow for only 450 psig. At higher design temperatures, however the maximum allowable pressure for 321 is greater than 9 Chrome.
John