Grade 660 Class A,B,C Fastener Rusted. 6

[ram1817]

ASTM A 453 grade 660,class A,B,C and D fastener rusted in our system and now I am looking for reason why this material rusted by looking properties and High temp fasteners this is the best fastener to use as per knowledge to high strength and high temp application.We used 316SS washer with this bolt its ok or not?Some of those bolts are mixed with black oxide coating may be thats the reason to rusting those bolts.
I am not getting any conclusion on this and getting more and more confused Please help me. These fastener are used in seawater application.Any alternative for 660 bolt?
What if i do passivate these bolt and use it it give me more corrosion resistance or not?
Thanks in Advance for help.

 

[SJones]

Without CP, in a tight crevice, in seawater - it is not surprising that the bolts 'rusted'. It is the wrong material if there is no CP.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[TVP]

Just to clarify for those who may not be familiar with the abbreviation, CP means cathodic protection.

Here is an excerpt from NORSOK M-001 (Rev 4, 2004) Materials Selection:

The following materials are regarded as immune to corrosion when submerged in sea water:

• titanium alloys;
• GRP.

Alloy 625 and stainless steels with PRE ≥ 40 are borderline cases and should not be used for mechanical connections without cathodic protection when their material temperature exceeds ambient North Sea sea water temperatures. Threaded connections are particularly susceptible to crevice corrosion.

For comparison, Grade 660 (A286, UNS S66286) has a PREN of 16.8.

 

[cloa]

PRE- Pitting Resistance Equivalent
PREN- Pitting Resistance Equivalent Number
PREN- A number calculated by from the composition that attempts to describe how resistant to pitting that an alloy is. I assume NORSK has its own particular formula.

 

[ram1817]

Can we use ASTM A193 B8M,class 2 material in alternative of 660 material.

I see properties of Alloy 625 :Tensile Strength (KSI) 120
Yield Strength (KSI). while grade 660 , Class D :Tensile strength 130(KSI) and Yield properties -105 (KSI).

Any Coating on 660 material can help to prevent corrosion.Can we do CP on 660 material.
Thanks

 

[ram1817]

We used this fastener in subsea system in pressure regulator.

 

[SJones]

Just make sure that there is a continuity lead from the cathodically protected item to the pressure regulator. It's down to whoever is responsible for assembling the equipment. If there is no CP, the best you can do from A193 is grade B8MLCuN.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[TVP]

cloa,

Thanks for the clarification of PRE/PREN. I should have realized I was introducing two undefined acronyms...


ram1817,

1. ASTM A193 Grade B8M (equivalent to ISO 3506-2, Type A4) is not immune to corrosion in seawater, which is why it is only allowed for above water applications in NORSOK M-001. For subsea applications that do not use CP, Alloy 625 (UNS N06625) is recommended/required.

2. Alloy 625 has a lower yield strength than Grade 660 Class D, 60 ksi vs. 105 ksi.

3. Coatings are not recommended for use with Grade 660.

4. I agree with SJones, Grade 660 Class D is ok with CP, provided that the yield strength is below 150 ksi. See NORSOK M-503 or DNV-RP-B401 for more information on CP. The following is an excellent reference on the subject of fasteners for subsea applications:

Engineering Failure Analysis 16 (2009) 1195–1202 Prevention of failures of high strength fasteners in use in offshore and subsea applications by Khlefa A. Esaklul (BP Exploration).

 

[ram1817]

Last Question to you guys.
our whole system is stainless steel so we don't have cathodic protection on system.
Now my question is :Astm A453 660 material is not recommanded to use in sea water if system is not cp? Can I replace those bolt with Astm A193 B8M class 2 bolt? what other option i have on this strength?

TVP : I Read "Preventation of........." In this article they said stainless steel bolt is not prefered if yield strength is more than 120 KSI and hardness is more than 34hrc.
B8M Properties: Yield strength : 95KSI
Tensile strength : 110KSI.
HArdness : 35hrc.
B8M is not recommnded to use in seawater?

Thank you very much TVP and Steave for your help.

 

[cloa]

You can still have cathodic protection for stainless steel- its often recommended.

http://www.onepetro.org/mslib/servlet/onepetropreview?id=OTC-1462-MS

http://www.stainless-steel-world.net/pdf/11004.pdf

 

[TVP]

ram1817,

Question 1) Astm A453 660 material is not recommanded to use in sea water if system is not cp?
Answer 1) ASTM A453 660 is not recommended for seawater use without CP. It does not have sufficient resistance to crevice corrosion and pitting corrosion.

Question 2) Can I replace those bolt with Astm A193 B8M class 2 bolt?
Answer 2) No. B8M does not have sufficient corrosion resistance for long-term use in seawater. As I referenced earlier, PREN should be > 40 for subsea use when CP is not used. B8M has PREN ~ 22, which means it will experience corrosion, especially pitting and crevice corrosion.

Question 3) what other option i have on this strength?
Answer 3) For high strength (yield > 100 ksi) fasteners, there are quite a number of suitable options, as shown in Table 1 of the Engineering Failure Analysis article by Esaklul. Here are two of the the Conclusions from that paper:

- High strength nickel alloys have high resistance to hydrogen embrittlement and are ideal candidates for high strength subsea bolts.
- Several other materials such as Custom 455, PH13-8, MP159, Ti–15V–3Al–3Cr–3Sn and Ti–10V–2Fe–3Al have the EAC resistance and are good candidates for consideration for subsea applications.

If you can add CP to the system, then ASTM A453 Grade 660 can be used, as well as Alloy K-500, 22% Cr duplex stainless steels like 2205 (UNS S31803), or even ferritic steels from ASTM A193 like Grade B7, B7M, and B16.

 

[EdStainless]

PREN is actual pitting resistance equivalent with Nitrogen.
The original PRE work (German) did not include the effect of N.
When using these numbers you need to know a few details.
- What multipliers does the equation use? There a number of versions. This is critical.
- What chemistry to use? Specification minimums or typicals? Many of the high alloy grades are more or less proprietary and are made to very narrow chemistry ranges.

These numbers can be used to rank alloys, ASSUMING THAT THEY ARE MANUFACTURED SO THAT THEY HAVE OPTIMAL CORROSION RESISTANCE. And in reality that is a very big assumption.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[ram1817]

Thank you very to you all.

 

[dik]

EAC... environmentally assisted cracking?

Dik

 

[metengr]

Yes.