Brinell Hardness

[Moersleutel]

Hi All

How is acceptable hardness values determined for material/HAZ/weld metal on API 650 tanks? The material is ASTM A 516 Gr 70 and PWHT to API 650 is done due to wall thickness.

Should this have been determined during weld procedure qualification or does published acceptance ranges exist? Some petrochem companies limit the hardness to 200 Brinell, but API 650 specify Rockwell C 22 (~237 Briness) max for HIC conditions.

Any tips?

 

[johnnymist2003]

Hi,

if the tank is in HIC service, you could look at NACE MR 0175 or 0103 for guidance, though these are mainly for pressure retaining equipment (eg. vessels).I'm not a metallurgist, but hardness can be directly related to tensile strength, the higher the hardness, the higher the tensile strength.In HIC equipment, the hydrogen attack can occur in areas of high hardness (eg. weld HAZ).If the weld hardness is a lot greater than the parent metal, it would make sense that the hardness would mean preferential attack in the HAZ.I would say tht the ideal situation would be to get the parent material/HAZ/weld hardnesses as cloe to each other as possible.API also referneces the material specs in ASTM, review these, hardness values may be listed.The 22C hardness value listed in API 650 for HIC tanks can be found in the NACE documents.
John

 

[DrillerNic]

API and NACE specify Rockwell C as it is a US hardness testing method. Other national code or Petroleum company codes may specify Rockwell C or Brinell or Vickers- I knew one metallurgist who always specified Vickers hardness tests as this is diamond shaped indenter rather than a spherical shaped intenter and the diamond indent is easier to see & measure than a spherical indent (and from personal experience doing these tests, I think he had a point!)

http://www.gordonengland.co.uk/hardness/

as a full listing of approximate equivalencies for HV10 Rockwell C, Brinell etc

 

[SJones]

Since you are applying PWHT there shouldn't be too much to worry about. Yes, ideally, the PQR should have included hardness testing; however, if you need field confirmation, investigate the use of an Equotip hardness measuring device coupled with a procedure that complies with ASTM something or other for portable hardness testers (sorry forgot the number).

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[PatrickMorton]

The guiding codes and criteria for what you are asking start with API 650. In there it will callout reference to ASME B&PV Section IX for welding and the requirements for procedure and qualification. From there it will also reference you to ASME B&PV Section V NDT. It is within this section that it will outline the method of testing and the acceptance criteria. There are several additional codes that are cross referenced that are part of the initial design process.

The best idea is to start with the API 650 manual and follow the path through the different codes.

 

[JoeTank]

API-650 requires the purchaser to specify hardness requirements. Since it is not a requirement of the standard, this is obviously something done thru a project specification. I believe that API allows it to be done by checking the as-welded condition or including it in the WPS/PQR.

I'm a bit confused, API-650 does not require tanks to be PWHT. Why is your tank being subjected to PWHT?

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[Moersleutel]

Hi

Thanks for the replies. The tanks is stress relieved according to the requirements of API 650 par 3.7.4. The tanks are quite big - 25m high x 34m ID and 21mm bottom strake thickness.

Regards

 

[JoeTank]

API-650 does not require that tanks be subjected to PWHT. Only the shell openings require PWHT as a sub-assemblies before installation into a tank. Are you doing PWHT as a service requirement? In the early 1980's I was involved with PWHT of an entire tank (45m diamter x 13m high) that was used for caustic oada storage. That was a real adventure.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com