My name is Chris Jones of Materials Performance Technologies (www.matperf.com). I have been involved with ultrasonic examination of three ammonia plants and one oil refinery for inspections for high temperature hydrogen attack. I have found hydrogen damage to varying severity levels in one HT shift vessel, two LT shift vessels, converter areas, two methanators, 1 secondary reformer and even mild damage in 1 desulphurising unit of an ammonia plant.
I have found extensive damage in associated pipe work in these plants. I have found the damage in parent material, weld metal and heat affected zone regions. I have found damage in forgings and in heat affected zones of weld repairs in cast elbows.
In all cases the pressure equipment had the potential for hydrogen embrittlement according to the most recent Nelson curves of API941 and the material of construction was in all cases carbon half molybdenum grade materials. The reason for the relatively recent known susceptibility to hydrogen damage was associated with awareness provided by the recent changes to the Nelson curves in relation to carbon half molybdenum material 1997 - API941.
The ultrasonic methods I employ (backscatter and a combination of velocity ratio and attenuation testing methods) are suitable for detection of hydrogen damage and in many situations I can provide an indication of the severity of the damage. The problem I find with procedures that I have developed which attempt to classify damage is that hydrogen damage occurs differently for different materials. Factors such as steel cleanliness dictate how damage will manifest in various materials.
I have published at the International Conference on Pressure Vessel Technoliogies (ICPVT 9) and soon intend to publish again devulging many of the things I have learnt since my original encounters with HTHA.
If you are intending to undertake inspection I can provide advice on where to look and how to look for the damage.
Regards, CHris Jones.
: I (My company) have a problem with hydrogen embrittlement at BFW-Synthesis ammonia exchanger, and I need newest information about Nelson curve. Please give me some information about it. . : Best regards : eko .
02:17 Jun-14-2001 John O'Brien Consultant, - Chevron ETC , USA, Joined Jan 2000 278
Re: hygdrogen embrittlement API 941 publishes the Nelson Curves and the expected susceptability to Hydrogen Damage. You should be consucting a rsik assessment based on materials, tempertures and partial pressure to determine possible susceptability.
Different operators report slight variations in experience with when HTHA attack occurs. Some prioritise Risk 1 above the C 1/2 Mo Curve and Risk 2 those withn 50 Degrees F of the C 1/2 Mo Curve.
There has been a recent roundtable discussion at the Sprin API Refining Meeting on HTHA and the various NDT approaches to looking for and assessing it.
Most people are using some form of Velocity Measurement and Backscatter Technique.
The number one issue is you need experienced personnle or you need to train people to do this type of work to get good results.
Re: hygdrogen embrittlement : Sir: The evaluation of Ammonia plant equipment for high temperature hydrogen attack and other mechanisms is comprehensively documented in a publication from last years AICHE Ammonia Safety symposiun. The paper(Written by G.R. Prescott / Brian Shannon) describes the parameters for the degradation and covers the latest in its detection and assessment techniques.The content on field inspections covers experience from over 250 Ammonia and Refining plants worldwide. Please refer to our web page for details on this and other field services that are available from IESCO .