Alloy 625 Overlays on Carbon Steel - Cracking
Alloy 625 Overlays on Carbon Steel - Cracking
(OP)
It is a fairly common practise to overlay carbon steel componenents with alloy 625. Valve seat pockets and flange ring grooves are two applications which I have encountered many times in the petrochemical industry.
Recently, I heard about a crack like failure between overlay and carbon steel in a valve for sour gas service. The failure was described as "fusion line disbondment caused by hydrogen diffusion".
Does anybody else have experience or knowledge of such failures?
Recently, I heard about a crack like failure between overlay and carbon steel in a valve for sour gas service. The failure was described as "fusion line disbondment caused by hydrogen diffusion".
Does anybody else have experience or knowledge of such failures?





RE: Alloy 625 Overlays on Carbon Steel - Cracking
It is very common in the Oil & Gas Industry to overlay specific areas of the valve with 316 and now more commonly 625. This is generally applied at the customers request where there is a seal in contact with the bare carbon steel. It is normally applied where there is a particularly corrosive environment, so that the area adjacent to the seal is not corroded providing a route for leakage and hence premature failure.
It can also be applied throughout all wetted areas of the valve and this is in preference to a solid 625 valve which can be very expensive. The route to go solid 625 or carbon steel is dependant upon the valve size.
As to premature failure of the coating i.e. disbondment caused by hydrogen diffusion I have not seen it in practise but believe it was a major problem on the BHP platform in Liverpool Bay project in the UK. The corrosion apparently started at the base metal and 625 overlay interface and caused bistering and eventual blistering of the overlay.
I trust this helps
RE: Alloy 625 Overlays on Carbon Steel - Cracking
It was the reported BHP failure(s) which had me worried.
The use of overlays is so common I assume that the BHP failure is specific to BHP rather than a generic problem.
In our sour service application, we have qualified overlay procedures in accordance with ASME IX and NACE MR00175. Weldments were tested (bend, toughness, hardness, chemical analysis). Hardness results in particular were good (180 HV10 typically).
Production welds were checked visually and with dye pen to ensure to machining deffects or cracks.
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
The whole of science is nothing more than a refinement of everyday thinking!!!
RE: Alloy 625 Overlays on Carbon Steel - Cracking
Some of the valves were replaced in service 1 - 2 years ago so there should be some sort of report available as to what caused the problem. If you have any contacts at Score Europe they might be able to provide some info. I will also contact Score and will publish any info. I receive.
RE: Alloy 625 Overlays on Carbon Steel - Cracking
Based on my investigations so far I believe that it is essential to ensure that overlay welding procedure provides hardness less than 22HRC / 248HV10 as per NACE MR-01-75.
I have contacted ITAG to establish the cause of the problem on Liverpool Bay and await a response.
djwright
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
I didn't see any mention of UT in the list of NDE integrity checks. We typically UT'd our overlays to check for unbonding. It isn't hard to do.
Unbonding of the overlay would be a workmanship problem for us. It would be caused by tramp contaminants or lack of fusion during a process or operator related discrepancy. Alloy 625 to carbon is nice to weld.
The hydrogen would need some unbonded region to start blistering. Tramp oil might do that and it would be missed using VT and PT. Just a thought
Koz
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
Liverpool and North Wales Materials Society
Programme 2003/04
06 Nov. Materials in Sour Service and other things that might crack
Presented by Dr Ed Heaver Liverpool Bay Asset, BHP
Location: Univeristy of Liverpool George Holt Building
17.30 Refreshments - 18.30 presentation
http://lnwmatsoc.liv.ac.uk
I will try and attend and provide soem feedback
RE: Alloy 625 Overlays on Carbon Steel - Cracking
RE: Alloy 625 Overlays on Carbon Steel - Cracking
Steve Jones
Petroleum Development Oman LLC
Muscat
Sultanate Of Oman