Tony,
Ryan is correct recommended hardness values for Gr.91 weldmetal are not listed as a code requirement in B31.1. There are several technical references you can use for comparison values though. ASTM uses 248HB as a maximum base material hardness requirement in A335 a seamless piping specification. At my company we use a hardness range of 190-270HB for Gr.91 weld metal. The point is to effectively temper the weld metal while not over-tempering the base material which will lead to reduced creep life properties. If the hardness is above 320HB and in an uncontrolled environment there is additional risk for stress corrosion cracking of the weldment prior to pwht.
Much research in this area has already been done. One project with the Electric Power Research Institute EPRI was made free for public download to better educate the Industry. It is titled "Guidelines and Specifications for High-Reliability Fossil Power Plants Best Practice Guideline for Manufacturing and Construction of Grade 91 Steel
Components". This document is available from EPRI.com search for report number 1023199.
One last piece of advice. Field hardness testing depends on equipment selection, technician competency, area preparation, calibration blocks, etc. Before you place a large amount of confidence in hardness testing numbers make sure that your process is appropriate for the application. I use both the MIC-20 w/ 10kg load and a PinBrineller our calibration blocks are made from Gr.91 material. Our inspectors receive 40 hrs of training before testing in the field. Understand the specification requirements for hardness testing. I found it very difficult to test the HAZ with a hardness tester consecutively. On large circumferential welds (greater than 5"OD we typically test 4 points on the weldmetal 90° apart. We also test 6" from the weldment to understand base metal condition.
Download the EPRI report for reference and good luck,
Michael J. Crichton, PE
Welding Engineer / NDE Level III
Metallurgy, Welding & Standards (MWS)
| "Ryan Carbonara" <rcarbonara@valv.com> Sent by: materials-welding@googlegroups.com 01/02/2013 10:21 PM
|
|
Client call typically. You wont find it in B31.1
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Anthony Rudder
Sent: Wednesday, January 02, 2013 11:37 AM
To: materials-welding@googlegroups.com
Subject: [MW:16411] HardnessP-91 Material
Sir,
What’s the Max hardness for weld metal and HAZ for P-91 Material per B31.1
Thank You,
Tony
QA.Manager.
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