What makes a Carbon Steel HIC Resistant? 4

[green1959]

Could anyone explain what makes a Carbon Steel HIC Resistant?

I am involved in a relatively small fabrication in the UK, where the materials of construction are specified as ASTM A333, A350 LF2, P355, A420 WPL6 but the materials are also specified to be "HIC resistant Carbon Steel".

What steps do we need to take to ensure this requirement is met?

Thanks in advance

 

[metengr]

The HIC resistant steel plates are a special product order that involves melting practices resulting in low sulfur contents (usually less than 0.002 w%).

Without getting into too much detail, the following publication by Bethlehem Lukens describes their HIC-Tested pressure vessel plate steels.

http://www.bethsteel.com/customers/pdfs/pressure.pdf

 

[CoryPad]

In addition to low sulfur, keeping strength/hardness down (below ~ 23 HRC) is considered an important feature for steel that is used in hydrogen-containing environments.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mcguire]

CoryPad has the right criterion. Hardness is the single key factor that must be controlled. I would be more conservative than CoryPad. I would say HRC 22 max.

 

[YLWEA]

NACE International has recommended practices for testing HIC resistance (NACE TM0284-2003). A corresponding DIN standard is DIN EN 10229. In the oil&gas industry it is not uncommon to specify that materials meet a certain performance level in those tests (or variations of those tests). see

http://www.techstreet.com/cgi-bin/detail?product_id=1086107

for a brief descirption and orering info for the NACE doc.

 

[CoryPad]

mcguire,

Thanks for your concurrence. Just to clarify, if we maintain two significant digits, then < 23 HRC IS 22 HRC max. This number is a guideline, but low sulfur, low segregation, and low grain size all allow higher hardness material to be used.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mcguire]

Adding to CoryPad's insights, I add that HRC 22 max ( i.e less than 23) is a maximum number. Failure is possible at lower hardness levels if microstructure causes lower toughness. Also this threshold decreases to lower hardness as temperature decreases.

 

[YLWEA]

The maximum hardness cited above is pertinent to sulfide stress cracking typical of excessively hard heat affected zones of welds in sour oil&gas production and processing. Similar problems occur in refining environments, although the refining guys often (or at least used to ) use a different hardness criteria. However, the hardness limit will not prevent hydrogen induced cracking (HIC) manifested as blistering or step-wise cracking that has an appearance similar to lamaellar tearing. HIC can occur remote from welds and is typically associated with the presence of pancake shaped sulfide stringers. Low sulfur and inclusion shape control are the most common method of preventing HIC.

 

[YLWEA]

I should have added that even though sulfide stress cracking and the related hardness limit is ofetn a welding issue addressed through carbon equivalent limits and appropriate welding procedures, the cracking problem can certainly occur remote from welds if the hardness is too high and adequate stresses are present.

 

[Cello]

For severe sour service, I would highlight more on the top of what has been correctly mentioned in this thread the calcium treatment (CAB, CaSi wire) to control the inclusion shape during steelmaking process as it improves a lot the HIC resistance. As a matter of fact, through this method the typically MnS sulfide stringers are then tranformed into globular shape, and this morphology is really advantageous for HIC resistance. In order to have a correct and balanced heat analysis for this purpose, one should require the ratio of Wght.%Ca/Wght.%S to be in the range of 2 to 3.