Here's some food for thought which I feel supports nearly every contributors thoughts on this subject
I will offer only pertinent excerpts and will leave out the scope which Shane has already provided.
Specification for Wellhead and
Christmas Tree Equipment
ANSI/API SPECIFICATION 6A
TWENTIETH EDITION, OCTOBER 2010
EFFECTIVE DATE: APRIL 1, 2011
6 Welding — General requirements
6.3 Pressure-containing fabrication weldments for bodies, bonnets, end and outlet
connections, bullplugs, valve-removal plugs and back-pressure valves
6.3.2.3 Welding procedure qualifications
The following apply:
a) written procedure:
Welding shall be performed in accordance with welding procedure specifications (WPS), written and qualified
in accordance with ASME, BPVC:2004, Section IX, Article II. The WPS shall describe all the essential,nonessential
and supplementary essential (if required; see ASME, BPVC:2004, Section IX) variables.
6.3.2.4 Welder performance qualification
The following apply:
a) testing requirements:
Welders and welding operators shall be qualified in accordance with ASME, BPVC:2004, Section IX,
Article III.
From our Northern neighbors. I thought it was appropriate for this thread. The full document is online and available free here
http://www.enform.ca/media/3675/irp5_final_2005.pdfMinimum Wellhead Requirements
Industry Recommended Practice
(IRP)
Volume 5
Sanctioned
2002 - 06
5.4 Field Welding Installation Procedures
IRP 5.4.1
Field welding installations of casing bowls, casing extensions and bell nipples must be done by a welder qualified to undertake pressure welding.
ALERT
The failure of a weld connection on a casing bowl or bell nipple has potential serious consequences.
Correct field welding procedures, particularly the application of adequate pre-heat and cool-down requirements, are often not followed. This occurs for two reasons.
Firstly, in most cases the steel composition of the materials being welded is not known by the welder. This is due in part to the large variation in steel composition that exists in oil field casing products, even within a particular grade, and in various manufactured wellhead components such as casing bowls and bell nipples.
Secondly, many of the welders being used do not have a documented Quality Assurance Program to follow. ASME Section IX should be referenced for information on welding procedure specifications and welder performance qualification.
Operators are encouraged to address the concerns related to field welding practices by developing their own standards. The following options are provided for consideration:
Use threaded components where appropriate and eliminate the need for a weld.
Establish a controlled inventory of casing of known material composition for use as landing joints and develop a welding procedure specification (WPS) for each size of casing.
Use a qualified welder from a contractor that follows a documented Quality Assurance Program.
Establish a welding procedure specification (WPS) for the specific materials being welded in each instance.
API RP 5C1 18th ed. may 1999, reaffirmed Aug. 2010
Recommended Practice for care and use of casing and tubing
9 Field welding of attachments on casing
9.1.6
The responsibility for welding lies with the user, and results are largely governed by the welders skill. Weldability of the various types and grades of casing varies widely, thus placing added responsibility on the welder. Transporting a qualified welder to the job rather than using a less skilled man who may be at hand will in most cases prove economical. The responsible operating representative should ascertain the welder's qualifications and, if necessary, assure himself by instruction or demonstration that the welder is able to perform the work satisfactorily.
And Lastly,
A large oil and gas exploration co. in North America performs hardness testing, PMI, CE of the casing to determine which WPS they will use for the welding. VT,MT/PT, RT will be used on the completed weld. No mention is made as to the welders qualifications. Of course that document is controlled.