welding old pipe to new pipe of P91 3

[akas1968]

Dear expert engineers,
would anybody help to suggest any special precautions to be taken while welding 10 years old P91 pipe of Main steam to new pipe?
thanks in advance.
Akbar1968

 

[davefitz]

2015-10=2005. The asme code sect I ( and B31.1) had a major change in P91 procedures after 2005, so I would use the provisions of the latest ASME code vis vis P91 welding as the first precaution. You may also obtain some assistance for this endeavor by contacting a metallurgist from one of the major boiler companies. Some items that come to mind:
a) confirm the lineage of the new P91 pipe; if it was from China and the material certs were themselves forged, you may wish to reconsider the use of that pipe
b) grind away the 2005 HAZ and weld to parent metal
c)preheat and PWHT as defined in the latest version of B31.1 . Monitoring thermocouples to be applied to both the weld zone and also directly underneath the pipe sections that are blanketed by the heating coils as per latest AWS guidelines, to ensure the sections under the blanket are not overtempered during heat-up.
d) double check that the welder's procedures follow "low hydrogen procedures", and triple check that the weld wire used for both the root pass and filler are not "rogue materials". Trust me, there is a lot of rogue material out there.
e) formally document ( and archive) the thermocouple readings of preheat and PWHT and the batch number of the weld wire.

"Nobody expects the Spanish Inquisition!"

 

[metengr]

I will add several steps not addressed above, after (b) perform a wet fluorescent MT to ensure sound material before welding.
(c) after welding cool the weld region to below 200 deg F before PWHT, this is important to avoid retained austenite and prevention of fresh martensite during PWHT. Perform PWHT as soon as the temperature has reached no less than 200 deg F.
(e) perform a volumetric examination of the completed weld and surface NDT.

 

[oumm]

Hi, please somebody can help me?a welding procedure is being qualified for use with a vessel that will require impact testing ; the coupon will be 4 inches . how many Charpy specimens will be required total?
how many set do we need for that test?

 

[EdStainless]

oumm,
1. don't hijack threads, start a new one
2. The number that the user has specified. If left to my own decisions I would use 4. Discard the outlier (after the statistical test) and average the others.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metengr]

how many Charpy specimens will be required total?
how many set do we need for that test?

You follow the requirements of the original code of construction for the vessel.

 

[davefitz]

For a recommended summary of the relevant metallurgical and practical experience on welding P91 , I would recommend this 491 page powerpoint presentation given in 2011 in India. It was titled " Fab 91" as part of an international workshop on the fabrication of P91. The presenters were the top metallurgists from the pipe mills, boiler mfrs, research labs, heat treatment contractors, etc. In addition to the theoretical aspects, many practical and proprietary correlations and guidelines are provided. ( I suspect one of the above responders were contributors to this presentation)
<

http://www.iimtiruchy.org/pdf/FAB 91 Final.pdf>

"Nobody expects the Spanish Inquisition!"

 

[danyyyy101]

New power plants are in high demand and several hundred can be expected to be built over the next decade. Chromium-molybdenum steel pipe (P91) is a major construction material in these plants and there are particular methods for welding it properly to insure it will hold up. Preheat and postweld heat treatment are mandatory and absolutely critical to the service life of the alloy. Induction heating is a growing method for preheating and postweld heat treating.

.Net