PREHEAT TEMPERATURE IN CAP PASSES 1

[Isildur78]

Hi everyone,

I´m currently in an offshore project, manufacturing K-nodes (code DNVGL). The material is S355 and the preheat temperature 100ºC. The thing is that all the welders complain about ,because of this temperatute, the beads of the capping are sharp and don´t comply with visual requierements of the project, so a lot of time is spent because of weld-grinding. Is it allowed in capping layer decrease a little bit (80ºC f.e.) the preheat temperatute in order to make capping beads less sharp?

Thanks!

 

[DVWE]

Under what code is the work being performed?

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

 

[gtaw]

Their problem isn't the interpass temperature.

Best regards - Al

 

[Isildur78]

The code is DNVGL.

 

[DVWE]

Sorry, I'm not familiar with that code. You will have to look into the code and see what the requirements are for preheat and interpass temperatures.


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

 

[DekDee]

What does the WPS state for minimum interpass / preheat temperature ?

To resolve your issue slap the welders around the ears and inform them that reducing the temperature of the parent metal by 20 degrees C will do absolutely nothing to improve the appearance of their capping passes.
A reduction in heat input (if noted in the WPS) is often used for the capping passes but never a reduction in parent material temperature.

 

[SJones]

As per DNV-OS-C401 (the assumed "DNVGL") it is quite clear that ANY decrease in preheat temperature is an essential variable requiring requalification of the welding procedure specification.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Isildur78]

OK, thanks for the answers!

 

[weldstan]

Thank you DekDee. This is more welder BS.

 

[M.CH]

Hi Isildur78

At first you shall check the record sheets of PQR. If the parameters recorded correctly you can follow them without problem. Appearance of weld pass mostly affected by welding speed, weaving,etc which controlled by welder in manual welding. By considering the range of essential variable, you can change these parameters and find the best combination.

If your code is DNV-OS-C401, decrease of preheat is not allowed and need re-qualification. you can let the temperature of last filling Pass( Under cap) drop to the lowest acceptable Interpass temperature.

Best Regards