The main difference between "on-plot" and "off-plot" is the construction codes. On-plot usually refers to plant piping (ASME B31.1 or B31.3)whereas, off plot refers to cross country pipelines (API-1104, B31.4 and B31.8). You would have to check your drawings and alignment sheets to determine where the class breaks are.

The E-7010 rod is a cellulosic rod that is made for downhill welding. The pipelines have a need for speed and the 7010 gives them that. Pipeline welders are a unique breed. They are used to welding downhill and fast. It is a different world from process pipe welding. E-7018, on the other hand is an uphill rod. Here you compromise speed for better puddle control. Fabrication, or combo welders are used to these rods.

If you have not already qualfied your procedures, you must and you must include the hardness tests, according to your posting. Besides, I do not know why anyone would want to qualify PQR's for sour service without performing hardness tests. If you have qualified your procedures and did not include hardness test, then you must requalify them with a new test piece. If this is the case and production welding has already begun, I do not personally see a need to cut out welds as long as the new PQR passes all the mechanical tests including hardness test. That is the clients call, however. Now I "would recommend", if you are going to use the same procedures for on and off plot piping, that you qualify your proccedures to ASME Sec. IX. Just make sure your parameters of your WPS's cover the ranges listed in API-1104.

The only difference between E-7010 and E7010 A1 is the 7010 is a high cellulose-sodium rod, and the A1 indicates a carbon-molybdenum steel electrode, probably about 0.50% Mo. You can get the actual chemical composition from the manufacturer.

The API 5L X42 tells me it is not a very ciritcal line. X42 is nothing more than ASTM A106 Gr. B. The use of X42 tells me this is most likely for construction of a new gas turbine power unit and not a gas plant. Am I correct? That is why I mentioned ASME B31.1 along with B31.3. Now, if you were to do chemical analysis and tensile tests on a sample of that pipe, I would bet you would find out it actually meets or exceeds API 5LX60 requirements. That is the steel in stock at most mills. You would actually have to designate X42 Max. in your PO in order for them to make a special batch of X42 for you. Cost is the big determination for using X42, I think.

I think your specs are reasonable. However, if you try to get your fabrication welders to weld like pipeliners and visa versa, you would only confuse everyone and probably end up with a higher repair rate, by no fault of the welders. If you want the same welders to do both jobs, just be patient and give them time to get used to the change, or get pipeliners. That I have experienced.

I would only add a couple of very minor comments to NDTIII's comprehensive and brilliant explanation.
1st. There is a small difference between API 5LX42 and ASTM A-106. The former may be either seamless or longitudinal welded whereas the latter can be only seamless.
2nd. The A1 suffix do means (not probably, but actually) 0,5% moly in the welded metal, provided the base metal contained that percentage. The actual percentage in the electrode may be somewhat higher to cope for volatilization.
Giovanni S. Crisi
Sao Paulo - Brazil

Just to add a little more info to the answeres given by the other respondents:

1) The major issue in sour service is hydrogen attack of the material.
2) Hydrogen attack tends to be worse where you have higher hardnesses. For this reason, the max hardness requirements.
3) The addition of even small amounts of Mo increases a material's resistance to H2 attack significantly.

Hope this helps

Regards
Niekie Jooste