Brinell readings acceptable highs and lows for Refinery heater tubes 2

[insp76]

Concerning the base metal at suspected flame impingement areas of Heater tubes, are there acceptable Brinell hardenss limits, high and low for safe operation.
I would like to know the acceptable high and low limits or good Engineering practice for 1.25cr, 5 cr and 9 cr tubes in refinery service. Any help would be appreciated, thanks.

 

[metengr]

In-situ hardness testing of heater tubes is at best not practical. For these tube materials, your main concern is going to be creep damage and wastage from corrosion (oxidation) associated with flame impingement or high than design elevated temperature service. I would rely more on thickness testing and tube samples to evaluate the condition of the tube material. Hardness testing, if performed, would be on tube samples removed for destructive examination where bulk hardness testing would provide for more meaningful results. The concern for these materials would be softening from exposure to elevated temperature service where bulk hardness would be below 65 HRB scale, versus new tube material at 80 or higher HRB scale.

 

[insp76]

Thanks for the response, yes we have thickness measurement history and we strapped the tubes as always. The biggest concern is softening and the loss of tensile strength beside the thinning . If the HRB is 79 and equals a Brunell of 143 the tensile strength is down to about 47K much less than the 80K for 5cr tubes and it seems this could be a concern because the heater was designed to run using 80K tensile strength tubes.

 

[Metaljon]

All materials soften over time when exposed to high temperature. I agree with Metengr that creep and corrosion are the major issues to address from the point of condition monitoring. A proper condition survey should involve replication, hardness and thickness testing. Replication can be used to provide a conservative life prediction. Hardness testing can be used as part of the assessment but the equipment has to be properly calibrated and hardness testing only on areas that have been polished for replication. If possible, samples should be removed for creep rupture testing to accurately determine remaining life.