Quiz- Section 7 Design and Preparation of a Joint for Production Welding – CWI Part C- 7 Questions
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Section 7: Design and Preparation of a Joint for Production Welding
The purpose of Section 7 is to establish requirements for production welding.
Production welding shall be performed only by qualified welders using qualified welding procedures. This paragraph identifies the cleanliness requirements for the surfaces to be welded. Further, any base material or handling conditions (e.g. lamination, tears, etc.) that might adversely affect welding are prohibited.
Ideally, the abutting ends of adjoining pipe lengths should align with little or no axial misalignment. In practice, this is unlikely, so API 1 1 04 suggests a maximum of no more than 1 /8 inch of offset (high-low) between adjoining pipe lengths of the same wall thickness. Larger variations are acceptable if the pipe meets the ovality (maximum and minimum diameter) requirements in the applicable material (or purchase) specifications and the offset is distributed evenly around the outside of the joint. API 1 1 04 suggests that hammering on pipes to obtain proper lineup be kept to a minimum.
7.3 Use of Lineup Clamp for Butt Welds
In production and fabrication, the use of a clamping device or fixture is a common practice to help bring adjoining pipe lengths into proper alignment. If external clamps are to be removed before completion of the root bead, at least half of the root bead must be in place, uniformly distributed around the joint. If internal clamps are to be used and removing them before completion of the root bead would permit movement of the pipe or result in undue stress on the unfilled joint, the internal clamps shall remain until the root pass is completed. When it is permissible to remove any clamp prior to the completion of the root bead, the completed portions of the root bead must be in approximately equal segments spaced approximately evenly around the joint.
Bevels placed on pipe ends by the pipe manufacturer, referred to as “mill bevels,” must meet the requirements of the welding procedure specification. Pipe ends may be beveled in the field by any machine tool or machine oxygen cutting. The company, however, must approve the use of manual oxygen cutting. The dimensions of these manual bevels must also conform to those specified in the applicable welding procedure specification.
7.5 Weather Conditions
Welding shall not be done when the weather conditions, such as airborne moisture, winds, or blowing sands, pose a significant threat to the quality of the completed weld. Responsibility for determining how or whether to conduct welding operations lies with the company.
For pipe welded above ground, the working clearance around the joint should be at least 1 6 inches in all directions. For pipe welded in a trench, the cavity beneath the pipe, sometimes referred to as the “bell hole,” shall be large enough to give the welder or welders adequate working space, but no minimum dimension is specified.
7.7 Cleaning Between Beads
Slag and scale shall be removed from each pass in a multi-pass weld using tools as specified in the welding procedure specification. High spots in beads deposited by semiautomatic or mechanized welding processes shall be removed by grinding to prevent contact between the filler metal and/or electrode and the weld deposit during welding. In addition, surface porosity clusters and bead starts shall be removed by grinding on semiautomatic and mechanized welds.
This requirement to remove slag from weld beads does not address the black “glass deposits” sometimes seen at the ripples of carbon steel weld beads deposited with GMAW. These deposits are black silicon oxide deposits whose black color comes from the manganese and iron in the base metal. Since they do not come from the flux used in flux-shielded processes, they are technically not slag. As a result, these are only required to be removed when specifically requested by the company.
7.8 Position Welding and 7.9 Roll Welding
For position (or “fixed”) welding, the pipes shall be secured against movement and the welders shall have adequate space to work. At the company’s option, roll welding may be used, provided the pipe is adequately supported to prevent sag.
API 1104 has established a target weld profile for all pipe welds, regardless of whether they are welded in the fixed or rolled position. Face reinforcement should be no more than 1 /1 6 inches and the face of the completed weld should be about 1 /8 inches wider than the width of the original groove. Note that this profile is a target, not a requirement. It is commonly referred to as “nickel-wide and dime-high.” In no case, however, shall the crown surface of the weld fall below the outside surface of the pipe. For both position and roll welding, the number of filler and finish ends shall allow the completed weld a substantially uniform cross-section around the entire circumference
In position welding, two beads shall not be started in the same location. Instead, the starts and stops of a multiphase weld should be located so that they do not coincide to avoid the creation of high-stress areas by multiplying the residual stresses associated with weld terminations. This applies to welds made in the fixed position, but not those made by roll welding.
7.1 0 Identification of Welds
Each welder shall identify his welds in a manner prescribed by the company.
7.1 1 Preheat and PWHT
Preheat and PWHT shall be conducted as specified by the welding procedure specification.