Transversal cracks carbon steel - steam line 1

[gbstanciu]

Hello everyone,

I have a weird situation regarding some carbon steel welds (base material P265GH).

We installed a Waste Heat Boiler and after 3 weeks of operation some welds in the main steam line generate transversal cracks.

We replaced the pipe and the fittings and make new welds. After other 3 weeks, the welds started to crack again.

On this line there is a spray water injection. It's possible that the water can contain some substances that can affect the welds in such way that can generate transversal cracks?

Thanks!

 

[kingnero]

Transverse cracking is less common than longitudinal cracking. Should be fairly easy to pinpoint the cause(s).
But not based on that picture! Are all of the white lines cracks? What's that monstrosity in the middle of the pic?

Without scale, can't say much however looks like a fairly wide weave. What was the heat input? P265 isn't hard to weld, but overmatching filler can be prone to cracks like those.
Cleanliness can be a factor, as well as hydrogen in the weld metal.

Chlorides usually don't attack carbon steel, but we don't know what filler is used. Problem could be there.

I'd retain a competent consultant or metallurgy lab, those will know what to check and be able to present you the necessary changes to your working methode.

 

[r6155]

This is a longitudinal crack (girth weld).

Regards

 

[r6155]

Did you see any RT after welding and after cracking?

Regards

 

[gbstanciu]

We used ER70S-6 as filler material.

I dont't think the filler material is the problem as we use in general this filler material for carbon steel welding. In my opinion I think there is not a problem of welding.

I've checked the RT films and they were clean. No pores were found that could generate further cracks.

The client sent some of the welds to a metallurgical laboratory for a detailed examination, but they do not found any issues.

I have attached a sketch with the configuration of the line.

My doubt is regarding the water that is injected in the line, it could be contaminated.

 

[MJCronin]

What are your design tempertures and operating pressures ? Did you pay attention to the piping configuration required by the desuperheater vendor ? ....Some DS vendors require a certain piping "straight length" both upstream and downstream .... Some DS vendors recommend schedule 80 for downstream piping

Is the piping schedule 40 or equivalent ?

Who is the vendor of your Desuperheater, or did you just have the maintenance department "make one up" ????

Have you considered an upgrade of material to erosion resistant low-alloy (A335-p11/P22) material ?... How about Stainless Steel (A312/376)?

Cracking in marginally welded CS piping downstream of desuperheaters is nothing new. When older fossil fired plants are inspected for refurbishment or life inspection, close attention and NDE is used on this section of the system.

These discussions might help

https://www.eng-tips.com/viewthread.cfm?qid=432085

https://www.eng-tips.com/viewthread.cfm?qid=247946

Tell us more .... can you show us pictures of the DS and piping layout downstream ?

Complete this thread by describing your next course of action and final solution ...

Anyone else ??

MJCronin
Sr. Process Engineer

 

[MJCronin]

Additionally, there is a lot of information in the Combined Cycle power industry about how improper DS operation can "quench" the inside of the downstream piping and induce cracking

https://www.ccj-online.com/avoid-de...nt-proper-installation-tight-process-control/

But, I am sure that your highly trained boiler operators would NEVER operate an expensive waste-heat boiler outside of the range specified by management, now ... would they ???

MJCronin
Sr. Process Engineer

 

[0707]

I am speculating, but from the foto it looks like some demage related with caustic embritlement. the welds had been PWHT? More detailed information is required for you get better answers.

 

[DVWE]

What do the welds look like from the inside (process side) of the pipes/fittings?



The devil is in the details; she also wears prada.

 

[gbstanciu]

Thank you for the informative links. I will start to review them.

The welds didn't required PWHT. We have check the hardness and it was under 200HV10.

In case of operating parameters of the boiler we don't have acces to them, but I am not so sure that they respect them.

I have attached a document with the configuration of the line and the desuperheater drawing.

 

[gbstanciu]

The welds are looking ok from inside (see the attachment)

 

[DVWE]

Doubtful it is anything process (spray water injection) related if similar cracking is not seen from the inside.

In case of operating parameters of the boiler we don't have acces to them, but I am not so sure that they respect them.

Personally, I would start with looking at and verifying operating parameters; if you're not so sure they are respected, make sure that they are. I agree with MJCronin that you should verify proper operations. From there, look at material upgrades such as P22 as suggested.



The devil is in the details; she also wears prada.

 

[0707]

Don´t you use sodium hydroxide to control water boiler PH? Operating windows are being respected? Did you made metalographs in the cracked welds? It is strange that the metallurgical laboratory do not found any issues about the failure.

regards

https://www.lenntech.com/abstracts/...stic-embrittlement-of-super-heater-tubes.html

https://rakhoh.com/en/caustic-embrittlement-in-steam-boilers-causes-and-prevention/

 

[Dhurjati Sen]

Is this an ADNOC plant in the UAE?

The main steam line piping, are they new?

DHURJATI SEN
Kolkata, India

 

[weldstan]

Transverse cracks are often due to contamination. From the ID photos, the cracks would appear to be not through cracks so they would not be fluid service related. Could a welder have contaminated the weld somehow?

 

[r6155]

@ gbstanciu
Can you tell us pipe diameter and thickness?

Regards

 

[gbstanciu]

@Dhurjati Sen - the location of the plant is in Europe

@weldstan - some of the welds were made in shop and some in site, but the welders worked clean; Like I've said above, we've repaired the welds which cracked first time, but again the same welds started to crack again. It's not possible that the welders can do the same mistakes.

@r6155 - the dimension of the pipe is ø219.1x8.18mm

 

[DekDee]

gbstanciu,
I agree with Weldstan - no evidence of cracking internally seems to remove the product as the cause.
And you are right, different welders, different scenarios but still cracking.
Was all of the weld metal removed 100% - or was only the crack gouged / ground out and then rewelded ?
The reason I ask is a totally different scenario but we still had the same outcome as you had.
A 3 mtr dia pressure vessel - C/S with the top half lined with Titanium.
Contractor had to grind a U prep just below the Ti to enable it to be sealed for hydrotest - they inadvertently touched the Ti with the grinding wheel and "smeared" Ti into the U groove.
After U groove was welded transverse cracks by the dozen.
No matter how many times they removed the cracks they still kept reappearing.
That is why I ask - did you remove the original filler metal 100% or just the crack ?
If the original shop welder has used the totally wrong filler metal and it is not fully excavated a totally different " field" welder may weld the repair and it will crack just the same.
Just some food for thought.
Cheers,
Shane

 

[r6155]

It can be a problem at the beginning and at the end of the welding bead.

gbstanciu. Were you watching during the weld?

Regards

 

[Dhurjati Sen]

Blue brittleness of the steel has taken place at the weld location.

Remove at least 2d length of pipe from each side of the weld and install a pup piece.

Carry out welding as before.

Have a good night's sleep.

Cheers

DHURJATI SEN
Kolkata, India