pre heating of alloy pipe

[eby5225]

As per B31.3, I understand all P11 materials has to be pre heated. So our client has asked to pre heat even for fit up also. Now the issue I am facing is regarding the small bore. I dont understand how I could preheat to 150 C and do fit up as it will be too hot to handle the fitting being small bore.

I understand pre heating is done to reduce the rate of cooling of weld to reduce the hardness. Hence is there any possibility to waive the requirement during fit up or any alternative method possible for fit. Looking for your comments

 

[racookpe1978]

Your client is - to be blunt - wrong.

The preheat is for the Heat Affected (Weld) Zone ONLY not for the whole pipe.

Their requirement is wrong, but you must be "diplomatic" in how you tell them that fact. Ask THEM to show you where THEIR reference is that THEY read so you can "review it properly" ... Simply but correctly telling them to 'shove it where the reg can't be read" is NOT a diplomatic answer.

 

[racookpe1978]

Are they somehow confusing a preheat condition for the usual pipe support pre-strain relief for hot pipes?

 

[weldstan]

Preheat is only required prior to welding. After fit-up and prior to tack welding, preheat is applied to the weld joint. Preheat can be discontinued after tack welding and then reapplied prior to root pass welding and weld out.

 

[metengr]

Don't confuse preheat for welding versus local or spot heating used to aid in alignment or fit-up for piping and nozzles.

 

[eby5225]

I believe my question may not have be clearly defined. The issue is I have do butt weld in small bore piping which is of alloy material. As per code pre heating is required before welding. Inorder to fit up I have to tack weld the joint. As per code, pre heating is required before welding. Hence the client is asking to heat the fitting before fitup. As the fitting are of small size, it is difficult to handle the fitting when it is heated to 150C. Any suggestion if tack welding can be avoided from pre heating.

thanks

 

[redpicker]

This is what I figured. How much time between the fit-up and the preheating prior to welding?

If I was the client, however, I would also require preheating for fit-up. Honestly, you run the risk of cracking without proper preheat, which you may not detect. Why should the client accept that risk? Can you use a mechanical positioner to hold the fitting after preheat?

rp

 

[metengr]

You can drop the preheat to a lower temperature as permitted by Code - see Section IX, it permits a maximum of a 100 deg F drop. Once the tack welding is completed, you can preheat again to the desired temperature. Check ASME Section IX.

 

[XL83NL]

Doesnt B31.3 overrule sect IX here since its a Construction code?
Ive always considered the 100F drop in sect IX related to procedure qualifications rather than Construction code requirements.

 

[DeleteriousPhases]

I'd suggest thicker gloves for the fitters to use. I have done fitting and welding and 150C isn't an issue if your gloves are thicker.

Switch to your tig gloves after the fit if you are using GTAW. Using a gauntlet with a thicker knuckle and a tig finger is a good idea. Thicker gloves aren't impossible with SMAW, though its nice to have that sensitivity that tig gloves provide.

Also, be religious with your interpass temperatures. Get out the temperature crayons, I regularly catch welders in our shop not using temp sticks to monitor interpass temperatures and have to order repair and reworks.

 

[metengr]

First, not all P-No 11A, B and C base materials require preheat. Second, B31.3 provides required and recommended minimum preheat temperatures depending on the alloy. Third, lowering of preheat is permitted for the WPS to allow flexibility in handling positioning and for tack welds in production without re-qualification of a new WPS.