Furnace Tubes with LME cracking 1

[DBreyer]

Hi all,

in a Naptha Hydrotreater Furnace with 5" tubes made from SS321 (in Service since 1978) on a piece of tube we removed for other reasons we, by chance, found external longitudinal cracking. Metallography revealed the cracks most likely being due to liquid metal embrittlement as they were intergranular and zinc was found on the fracture surfaces. Cracks progressed about half-way through the wall (6.6mm wall thickness)and were around 100mm long.

We are now looking for a NDT method that will allow us to identify if there are more ckracks in the rest of the furnace (~400m of 5" tubes).
- Intelligent pigging with eddy current or shearwave probes might be an option but so far we only used pigs with straight beams in furnaces (to find wall thickness loss). As there are short radius bends at the end of each tube I don't think an ILI tool made for pipelines will work. Do any of you have experience with pigging of furnaces with cracks? or do know a company that offers this?

- another Option might be using hand-held/guided eddy current probes on the outside of the tubes. However the tubes are scaled and due to the total length of the tubes we would need a rather quick method of testing. Any experience there?

- as a last Resort we are thinking about doing a pressure test ( calculating max. permissable test pressure and using that) in company with Accoustic Emission probes to detect any crack growth. Have you done something like that in a furnace before or on piping?

I'd be grateful for your input or any other ideas short of retubing the whole furnace.

 

[Dhurjati Sen]

The furnace was running with these crack(s) which you found out by chance. 42 years of service is quite enough, most plants are designed for 25 years.

Two options for you.

1. Don't bother.

2. Carry out guided USFD (H Scan). Of course, you need a clean surface for this (even for any NDE)

DHURJATI SEN
Kolkata, India

 

[DBreyer]

Dhurjati Sen, do you know of a company that offers guided wave crack detection in austenitc tubes? Couldn't find much on the internet and our typical net contractors ( europe) don't offer this

 

I'd want to do a complete metallurgical workup, but of course that would mean destroying one tube, not feasible for this equipment.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[Dhurjati Sen]

Dear DBreyer,

Google " H scan reformer tubes"

Good luck

Regards.

DHURJATI SEN
Kolkata, India

 

[0707]

I suppose your tubes have "creep" beyond which is acceptable, maybe more than 5%, so I is time to retubing the whole furnace. Try to make a LORUS testing.

luis