Transverse Cracking in Carbon steel welds 3

[numberfive]

Hello everyone,

I'm having a problem with transverse cracks in carbon steel welds on a low pressure steam header for a sawmill drying kiln operation.

The header is 20" STD SA-106 Gr. B with 20x20x10 WPB reducing tee's on either end for 10" dirt legs and a 20" WPB pipe cap on either end. The header has (2) ea. 8", 10", and 12" weld-o-let style branch connections with 150# RFWN flanges on each.

The header was built in 2022. Solid wire root passes (Miller RMD PipePro), flux core fill and cap passes. ER70S-6 and E71T-1M respectively.

Operating conditions are 10-12 psi. at around 250 deg. F.

The customer has had (3) leaks to date due to transverse cracks across the welds.

We just stripped all insulation and performed MT examination of every weld today and found a total of (1) transverse cracks.

Weld quality looks really good both on root and cap sides.

Has anyone experienced similar issues with carbon steel? Very strange.

Took multiple hardness readings today and all ranged from upper 150's to lower 170's HB both in weld metal and base metal.

Also took shavings for a chemical analysis of weld wire.

Thank you,
numberfive

 

[mfgenggear]

All great information and great brain storming. I want throw my 2 cents in the subject. As I had many years in a sheet metal shop while not directly related. There was lots of weld and NDT, and pressure testing. We had some of the best welders . And were very good at their jobs.
But depending on the material and weld type, NDT found many indications and defects. That required precise types of repairs or rework.
Radiographic , dye penetrant as well as magnetic inspect detected many defects not visible by eye. And many were only detected by radiographic or ultrasonic inspection.
But these are mostly longitudinal and rarely transverse if I remember correctly.
Regardless many indication or small Crack had to be drilled out and removed. If not trying to reweld them it would keep chasing and cracking.as I said very specific repairs are required.
Main case of cracking regardless is wrong weld fuller, improper weld preparation, improper of heating the parent material.
The initial or rapid heating of material , and quick cooling causes the material grain structure to stress and strain. The rapid heating and cooling causes material to crack.and if not heated properly. It's
All in the wps.

 

[r6155]

Even with Cat C joint on the o-let to WN flange weld, most likely it is just spot RT.

If someone designs with Weld-Olet (for butt welding with pipe or flange), it is for 100% RT, if not, he is a misguided designer with no experience in manufacturing and inspection. It is not an offense.

Regards

 

[mfgenggear]

So this may be a bigger problem. Than is just the visible cracks. The question is are some of theses defects are in the parent material as well. Or was it initiated by poor welding procedure.. a deep dive into the details and how were they fabricated and how were NDT tested. Cracks could have been initiated in the fabricaton cycle as well. A fishbone diagram is a very important tool to decipher what is not the cause, and eliminate possibilities.
Jumping to a conclusion could be a mistake of not detecting the exact cause and obtaining the correct corrective action.
Once the details are eliminated as cause then focus can be on the welding procedure, then on the possibilities of the wrong parent material for the processing of liquids or gas involved.