Hi Devang,
An operating temperature of 500-530 Deg C is fairly high for P11 steel. Though the design code provides the allowable stresses at that temperature I would say for that operating temperature range selection of P22 steel would have been a better choice. In the context of the refineries 300 series is very common so as to have the thermal stability and desired machinal properties @ 500-530 Deg C, why it was not chosen ??
Having said those, the hardness values 100-125 BHN too low for these steels. As fabricated and PWHT-ed( if applicable) hardness readings of 150-180 HB would have been appropriate.
Materials degradations in the creep range can't be concluded by hardness reading alone. The following additional inspections are warranted:
- Signs of deformations , swellings on the lines
- Replications for Creep Cracks/damages.
You may find additional guideline in API 571.
Thanks.
Pradip Goswami.P.Eng, IWE.
Independent Consulting Welding & Metallurgical Engineering Specialist
Saudi Aramco Approved Designated Project Welding Engineer(DPWR)
Qatar Petroleum Approved, SME-Materials & Corrosion Engineering.
Linkedin: https://www.linkedin.com/in/pradip-goswami-2999855/
Email:pgoswami@rogers.com,pradip.goswami@gmail.com
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From: materials-welding@googlegroups.com <materials-welding@googlegroups.com> On Behalf Of Devang Majithia
Sent: May 27, 2021 11:41 PM
To: materials-welding@googlegroups.com
Subject: [MW:32392] LAS P11 minimum required hardness for operation
Dear All,
Hope all are safe and doing good in this tough time.
36" LAS P11 steel is used in FCC Reactor O/H line with operating temperature of 500-530 Deg. C. Design temp. is 569 Deg. C. Creep temperature starts from 427 Deg. C as per API 571. Line in service for 10 yrs.
In situ metallography is taken and noted to be with pearlitic structure disintegration and dissolved carbides in matrix (at 500X). Refer pic.
We noted hardness in the range of 105-120 BHN which appears to be quite low against generally noted 160-180 BHN. Baseline reading is not available. Hardness measurement done with a portable machine having angle compensation.
Request to kindly guide me on how much minimum hardness is acceptable for P11 material for such critical service?
Regards,
Devang Majithia
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