Jon,
Of course more info is needed to provide much help.  One thing I can say is that you may face difficulty meeting both requirements, at the same time.  Sour service weldments (in carbon and low alloy steels) will require filler materials with less than 1% Ni.  Low temperature weldments, in the same materials, normally utilize filler materials with Ni, and depending on the temperatures, may require 2-3% Ni to meet impact requirements at low temperatures.

Depending on the "extremely cold" temperatures, you may have a problem.  I will look forward to more specific information on the subject.  Where is the work being done?

jon , keep us posted on what you need . i'll try to get you some contacts . i know they have been doing lots of welding in artic conditions . is this new construction or in service ? good luck . willie 

I suggest a few things on this, first of which is sour service is a pretty standard issue in oil and gas. The extreme cold conditions such as found in prudoe bay, and parts of the canadian oil efforts would be more the problem. If it's really cold, it will get into adding nickel sometimes as well as the standard low hydrogen efforts. Without specifics on temps and materials there's not much else that can be added.

Well - you're dealing with Sourdough aka "Alaskan Assassin" - what do you want to know?

Tok, Alaska 1999 -67

Siberia Ridge,Wyoming 2007 -36

"stacks, racks, nipples, and cracks - we got ya covered"

Do you at least know what your application will be? Pipe? Structure? Machinery?

Diffusible hydrogen is the enemy.  Absolutely clean joint preparation and consumables are essential.  Absolutely clean handling of the same is essential.  Houskeeping and workmanship cannot be overstated.  This will have to confront the usual urge for the production rush.  Long post weld hydrogen bakeout is recommended, especially for conditions with significant restraint.

Watch that many petrochemical applications have restrictions on Ni in the weld metal to 1% out of concern for SCC.  This may be based more on historical subjectivity than real, but the concern is still there and should be assessed.  Evaluate process fluid with potential for SCC sensitivity of the weldment.

Suggest to keep the preheat and interpass on the high side and weld beads small as feasible; to keep the deposited weld metal per unit length small, toward maximizing tempering and transformation of previous weld passes due to direct weld heat.  Everybody realizes this compromizes production efficiency, but the goal of certain high weld integrity should define the manufactured product.  Suggest run some repersentative test welds, section and metallographically prepare to a fine polish and etch to evaluate heat affects for respective parameters. 

Watch that the temperature extremes of the bulk base metal between farication temperatures and service temperatures accounts for geometrig thermal expansion and/or contraction in order toward minimizing the effects of thermal induced cold spring effects which may be concentrated at the weld.

As regards the base metal, ASME has many classifications of carbon steel materials that satisfy low temperatur service requirments.  There is significant added testing associated with this certification.  No material should be used on site that does not have the specific identification and material certification in hand.  User must verify that material cert conforms to product specification (eg ASME) in all respects and leave no stone unturned with this.  Given the tight supplies, many materials are comming from all parts of the questionable world, by way of a series of unconcerned international distributors before it is delivered to site.  The project should plan to spend money to verify properties should origin information be suspect. 

Project absolutely must implement a program of PMI for every peice used in production.  Imagine what would happen if a piece of P5 material were used where P1 is specified; a Canadian refiner did to the toon of 800M$.