Pre-Heating of Carbon Steel pipe with 20 mm wall thickness and at low ambient temperatures

[Delikado]

Dear Experts,

Our client has this requirement in their WPS regarding pre-heating of A333Gr.6 and A671 material(pipe) with nominal wall thickness of 20mm-50mm to min.temp of 100-120 deg.C and pre-heat maintenance is also required by using resistance heaters/gas torches, maximum interpass temperature 300 deg.C. Heat treatment is also mentioned(not an issue).

1) In B31.3 it only requires pre-heating of P-No.1 (Carbon Steel) wall thickness >25mm to 95deg.C at %C>0.30. Therefore it contradicts to our clients WPS parameters right?
2) We want to weld an NPS 80*20.62 Carbon steel pipe but currently we have below 10deg.C ambient temperature. How we can normally proceed? does the requirement in the mentioned WPS does make sense during welding at low ambient temperature? with regards to pre-heating and pre-heating maintenance?
3) Is there a risk of cracking if pre-heating is not adhered?
4) Any recommendation on how we can fully achieved pre-heating temperature if we will weld CS material at NPS 128 and WT>30mm?

Regards,
Delikado

Expecting life to be fair on you because you're a good person, is like expecting an angry bull not to charge on you because you're a vegetarian.

 

[XL83NL]

1) No, your client spec overrules (or actually; sets additonal requirements to) B31.3. Refer to B31.3 para 300(b)(1) and 300(c), all point, and specicially 300(c)(5).
2) What exactly do you mean with "but currently we have below 10deg.C ambient temperature"? Is it 10 °C ambient or -10 °C ambient? And which requirement do you mean with "does the requirement in the mentioned WPS does make sense during welding at low ambient temperature"? Also, you have an NPS 80 pipe, i.e. 2 metres diameter?
3) Yes
4) 3.2 meter diameter pipe? Not sure how you can do that.

 

[Delikado]

2) What exactly do you mean with "but currently we have below 10 deg.C ambient temperature"? Is it 10 °C ambient or -10 °C ambient? And which requirement do you mean with "does the requirement in the mentioned WPS does make sense during welding at low ambient temperature"? Also, you have an NPS 80 pipe, i.e. 2 metres diameter?

- it is 10°C ambient (sorry about that but soon we will have -10°C.
- I mean that requirement of Pre-Heating to 100°C, since we are only welding DN2000 pipe with wall thickness of 20.62mm as per B31.3 required is only 10°C
- NPS80 which is equal to DN2000.

4) 3.2 meter diameter pipe? Not sure how you can do that.

- What I mean is NPS128 approx. equal to DN3200 with wall thickness of >30mm.

Okay let us make it like this, WPS was prepared by our welding engineer and we both work in the same organization.

Regards,
Delikado

Expecting life to be fair on you because you're a good person, is like expecting an angry bull not to charge on you because you're a vegetarian.

 

[XL83NL]

As you brought up client requirements, there's something extra here need to be taken into account.
2) Review table 330.1.1. If your client does not specify anything additional to this, stick to the table.
4) Whats the carbon content? Does your client specify additional measures for preheating in their specs?

 

[Delikado]

4)%C=0.25, WPS states that Preheat temp. should be minimum 100-120°C ; Preheat Maintenance Resistant heaters/Gas Torches, so aside from WPS nothing else.

Regards,
Delikado

Expecting life to be fair on you because you're a good person, is like expecting an angry bull not to charge on you because you're a vegetarian.

 

[weldstan]

So you are using your client's WPS. This would assume that you have no WPS to support your work, in which case you need to follow the WPS given to you by the client. As ambient temps decline below 10 C, it is a good idea to preheat, especially below 5 C.

 

[metengr]

As stated above, follow your client's requirements. Preheating is a good practice for carbon and low alloy steel weld joints.

 

[DekDee]

If you are working to B31.3 then it is pretty likely your WPS is in accordance with ASME IX.
If so preheat is an essential variable.
Decrease greater than 55 degrees celcius of "that qualified" requires requalification.
As you are using clients WPS do you know what the PQR states regarding preheat ?
Was it qualified at 155 degrees celcius and subsequently reduced to 100 degrees on the WPS ????
Or was it qualified at 100 degrees ?
Irrespective of all the above you cannot weld using that WPS with anything less than a 45 degree celcius minimum preheat (100 minus 55 degrees as per QW 406.1)
Regards,
Shane

 

[DekDee]

In addition
B31.3
330.1.1 Requirements.
………………………Higher minimum preheat temperatures may be required by the WPS or by the engineering design.

 

[Delikado]

Thanks for all of your input guys.

Regards,
Delikado

Expecting life to be fair on you because you're a good person, is like expecting an angry bull not to charge on you because you're a vegetarian.