Are you referring to a destructive or non destructive test?
Is the pipe welded to a plate with a fillet weld?
Or is it a pipe to pipe groove weld?

Your supplier should provide you with a WPS and WQTR's for the welders that made the welds.
They should be inspected to the code that the work is being constructed to. i.e. ASME B31.1, AWS D1.5 etc.
Do you have contract documentation that specifies what test if any that are required for these parts? i.e. visual, MT,PT,RT etc.

If it is a fillet weld and you are just curious as to check behind the supplier then you can cut the part and Macro etch to check for penetration and fusion.
Of course this is a destructive test and might not be feasible or logical.

A little more info will help us help you with your question. Thanks.

Chandramouli,

I would require that my supplier weld my parts to industry standards, preferably with a welding procedure, using qualified welders, and equipment in good working order.

A welding procedure is basically a recipe.  It tells the welder what variables to use in welding your part.  Full blown welding documents including a PQR, WPS, and Qualification. They could include 50- 100 variables and require a 1/2 dozen destructive and non-destructive tests to "prove" that your part is "welded."

At a minimum, I'd want to know the material type, including wall thickness, process used, gas type, and filler material. 

It's kind of like if your car is broken and you take it to a mechanic and tell him you need a battery.  He installs a battery, but your car still doesn't work.

Communication.  Explain what you want, what you need, and what you expect.  Ask your welding source for options.  What would they recommend?

Keith