Where is the specification for 4140 L80-->NACE HARDNESS 18-22HRC

[katrinali]

Hi guys,

I am new to this industry and i found many threads saying NACE hardness require 18-22 HRC range, but i went through it didnt find the min HRC mentioned anywhere, could anyone please help me out where is the min 18 HRC hardness in NACE ? thanks a lot.

Regards
Q

 

[CoryPad]

The requirement is 22 HRC maximum, and it comes from ISO 15156 Petroleum and natural gas industries—Materials for use in H2S-containing environments in oil and gas production -- Part 1: General principles for selection of cracking-resistant materials and ISO 15156-2 Petroleum and natural gas industries -- Materials for use in H2S-containing environments in oil and gas production -- Part 2: Cracking-resistant carbon and low-alloy steels, and the use of cast irons.

 

[katrinali]

Hi CoryPAD,

Thanks for the reply, I do found the 22 HRC, but do you know where it was mentioned for 18 HRC ? i only found the 200HBW requirement in ASTM A193 ...
Thanks
Q

 

[CoryPad]

Anything below 20 HRC is not valid since the HRC scale starts at 20. You won't find anything official that states 18 HRC.

 

[metengr]

The concern is maximum hardness to prevent SCC. There is no reason to specify a minimum hardness in this type of application.

 

[katrinali]

Corypad--Thanks for the information , so the 18 HRC suppose to be customer requirement i guess..

metengr- i think the min is 16 HRC since the ASTM A193 require 200 BHN minimum...

Thanks for your comment
Q

 

[redpicker]

The minimum of 18 HRC is an industry-accepted minimum for L80 as evidence of meeting the 80 KSI min yield/95 KSI min UTS requirements of the grade. Not actually a requirement stated by API for this grade, it is commonly found throughout the industry.

While CoryPad is correct in stating that 20 is the minimum valid value on the Rockwell 'C' scale, 18 HRC minimum has been used for decades for this grade. Perhaps an example of how people who purchase and use Rockwell Hardness Testers do not thoroughly read ASTM E18, in any case it is a common requirement. Not too surprising, given that E18 is 30 pages long (not including non-mandatory appendices); quite a bit to describe a test method that takes maybe all of 5 minutes to train someone to perform (OK, perhaps a bit of hyperbole, but this is why so many people who perform a Rockwell test have no idea what the ASTM standard actually says).

The users of L80 want a maximum 22 to comply with the sour-service requirements (API 5CT allows a 23 HRC maximum, but many users require the 22 HRC maximum found in the NACE document). To be sure this is what they receive, they require hardness testing be performed on the material. Since they are paying for a hardness test, they also want to use the results to demonstrate that the minimum strength requirements are met. While, technically, the lab would have to change over to Rockwell 'B' (and re-calibrate the tester), most labs would want to charge for two tests (rightfully so, since they would have to perform two tests). A compromise is made to accept Rockwell 'C' readings as low as 18 as being valid and the world goes on.

This generally is not a problem, since as a practical matter, a Rockwell 'C' reading below 18 on L80 results from either the material not having adequate tensile properties or the hardness test being performed incorrectly. Since neither the material supplier wants to admit the former nor the testing lab wants to admit the latter, the technical issue of the requirement not being valid on the Rockwell 'C' scale is often quietly ignored.

rp