This activity includes functions related to the unloading, stockpiling, loading out, hauling, and stringing of pipe along the route. Pipe may be shipped by truck, rail, or barge and unloaded and stockpiled at previously selected strategic points along the line route. The pipe is loaded out from a stockpile onto stringing trucks and strung along the line as construction progresses. Stringing must be conducted so as not to damage the coating, dent pipe or scar bevels. Often stringing is done by a subcon-tractor specializing in pipe hauling.
Fig. 600-1 Angle of Repose for Sloping of Excavations Fig. 600-2 Excavation Benching for Compact Soil
Company field personnel should confirm that the stringing foreman has full infor-mation on the locations along the line for changes in pipe wall thickness and coating.
Prior to stringing, stockpiled pipe or pipe directly off-loaded from railcars or barges should be visually inspected. Cracked coatings, pipe that is dented and damaged in transit, and pipe with out-of-round ends normally should be repaired before being strung. Any transit damage should be documented so that claims may be made against the carrier and disputes with the construction contractor prevented. See Section 740 for recommendations on stockyard inspection.
Field plants for yard coating, double-jointing pipe, or both may be established at one or more stockpile sites. Special handling is required to avoid injury to the coating and may involve padded trucks and unloading with special hooks. Because of its increased length double-joint pipe may require special-steering pipe trailers regulated by law.
Bending
Changes in direction and elevation of the ditch require bending of the pipe to fit the contour. Side bends will be laid in a horizontal plane; over bends and sag bends in the vertical; and combination bends in three dimensions. Normally bends can be of sufficiently long radius so that they are bent in the field. Tight bends need to be made in a shop equipped for induction-bending and then shipped to the field.
Sections 320 and 330 of this manual cover bending of line pipe.
Care must be taken during field bending to prevent wrinkling of the pipe wall, flat-tening or buckling of the pipe, and damage to the coating. Bends should be checked to see that they are within tolerances for ovality. This may be especially important during the initial days of spread operation in the event that the pipe-bending
foreman is inexperienced or careless. Pipe bends that exceed tolerance for reduction in diameter may obstruct the passage of scrapers during testing. Also, a flat spot in the pipe is a point of weakness.
Small-diameter pipe, generally NPS 12 or less, can be bent satisfactorily using a bending shoe attached at the bottom of the boom on a sideboom tractor. The angle of bend is visually judged by the bending crew.
Bending of larger-diameter pipe is accomplished by horizontal or vertical bending machines powered hydraulically or by cable systems. The angle of bend can be closely controlled with the machine. Ditch angles are usually measured by the bending crew with hand survey instruments in advance of the actual bending opera-tion.
Each joint of pipe should be evenly strung end-to-end ahead of the lineup crew so that the position of the bend in a particular joint of pipe will fit the ditch when that joint is subsequently welded into the line.
Lineup and Initial Welding
The "pipe gang" performs the lineup of each pipe joint to the already-welded line, the initial root-pass ("stringer bead") weld, and the next ("hot pass") weld. (A
second "hot pass" weld is sometimes required by the welding procedure or to alle-viate a cracking tendency.) This crew generally sets the pace for the spread and thus is the "money-maker" for the contractor. Problems of quality workmanship and productivity of this crew are critical and must be resolved quickly; speed is desir-able, but it must not be achieved at the expense of good workmanship.
Equipment with the pipe gang includes two or three sideboom tractors, welding machines (often the "stringer bead" machine is mounted on one of the sideboom tractors), and usually a water-sprinkler truck to control dust as equipment and vehi-cles move along the construction working strip.
Before lineup, the beveled ends of each joint are thoroughly cleaned with power tools. The full length of the inside of the pipe is visually inspected for dirt and debris. A swab should be pulled through each joint to remove any dirt and debris.
A sideboom tractor moves the pipe joint into position for alignment and supports the pipe until the "stringer bead" is complete. The pipe is aligned with the aid of lineup clamps. Internal clamps are normally used on lines NPS 10 and larger.
External clamps are usually used on smaller sizes. The now self-supporting pipe is then lowered to timber skids along the side of the trench, and the "hot pass" is made before the weld area cools. Clamps are then removed and the process is repeated for a new pipe joint.
The longitudinal weld seams on adjoining joints of ERW or SAW pipe should be offset from each other by at least 3 inches or 30 degrees, whichever is greater.
Seams are normally alternated at the ten o’clock and two o’clock positions.
At appropriate intervals along the continuously welded line, a weld is not made, and an overlap of a few feet is left at the unwelded ends of the pipe. Later when the line is lowered into the ditch, "tie-in" welds will be made to complete the line. This allowance for tie-ins permits some expansion and contraction of the welded pipe without upsetting the skids and some adjustment of the pipe to the ditch during lowering-in that would not be possible if the pipe were welded in a continuous string. Since tie-in welds are more expensive and require more time than a produc-tion weld, there may be a tendency on the part of the contractor to neglect tie-ins and to weld up long straight sections of pipe continuously. This practice should be watched for by Company field personnel and corrected. The proper distance between tie-ins depends on local conditions and should be determined on the job.
The ends of the pipe at tie-in gaps should be capped temporarily with tight-fitting
"night caps." This prevents foreign objects and animals from entering the pipe between the time it is welded and the time when the tie-ins are made. Experience has shown that open ends will cause trouble later in construction—small animals may crawl in the pipe; pieces of wood, including skids, may be left in an open end and welded in; and dirt, weld rod, odd pieces of clothing, and other foreign objects are sometimes found. Contractors may wish to substitute burlap sacks tied over the ends of the pipe or may insert a skid half way, leaving half the skid projecting.
Neither of these alternatives is satisfactory.
Filler and Cap Welding
The "firing line" welders follow the pipe gang and complete the welding with filler beads and a cap bead. One or more filler beads may be required, depending upon the wall thickness and the particular welding method used. "Firing line" welders usually work singly to complete one or more passes at a weld, and then leap-frog ahead to the next series of welds needing filler and cap passes. "Firing line" welders normally own and operate heavy-duty pickup trucks mounted with an engine-driven welding generator and welding equipment.
Radiographic Inspection
After individual welds are completed and cooled, field radiographic inspection is done, following the inspection specifications. One, or more often two radiographers perform this work, using a radioactive source or a portable X-ray unit and a dark-room mounted on a heavy-duty pickup truck. Review and interpretation of radio-graphs of the day’s welding progress should be completed by the end of that same day and be available to the Company welding inspector periodically during the day.
See Section 750 for guidelines on radiography.
When 100% radiography is required, one radiographic team and equipment set is needed for production welding and a second for tie-ins and backup.
Weld Repairs
Welds requiring repairs, as determined by visual or radiographic inspection, must be clearly marked and visibly flagged so that they are not coated over. Repair work is usually done either by welders from the welding crew outside of regular working hours or more often by the tie-in crew welders. Repaired welds should be radio-graphed again.
625 Coating
Field Joints and Coating Repairs on Plant-Coated Pipe
Following radiographic acceptance of welds, a small crew puts on the specified coating at field joints, makes repairs to obviously damaged plant-applied coating, and inspects the coating with a holiday detector ("jeep"). The holiday detector must be operated and maintained in accordance with the manufacturer’s directions for the particular detector and coating. This work is done while the line is supported on skids. Heat shrinkable sleeves ("shrink sleeves") are most frequently used at field joints on extruded polyethylene, fusion-bonded epoxy, and coal-tar-enamel coated lines, and are manually applied with hand-held torches for heating. On fusion-bonded epoxy coated lines, an epoxy coating is sometimes specified—either painted on or fusion-bonded with field induction-heating equipment. Hot-mix Somastic field joints are used on Somastic-coated pipe. Whatever the field joint method, thorough cleaning of bare steel and overlapped plant coating is required.
Over-the-Ditch Coating On Bare Pipe
A large crew and specialized cleaning-priming-coating equipment is needed for this operation. Lowering the pipe into the ditch proceeds immediately after wrapping. In this operation one or more sideboom tractors with roller cradles lift the line up off the skid supports, moving ahead along the line. An engine-driven cleaning and priming machine, supported by a sideboom tractor, closely followed by an engine-driven tape-wrapping or hot-asphalt or coal-tar coating machine—also sideboom tractor supported—and finally one or more sideboom tractors supporting the line with roller cradles to guide the pipe into position in the ditch, proceed steadily ahead. The coated pipe is "jeeped" for holidays (defects) in the coating immediately after coating, and repairs are made. For tape wrapping, the operation is stopped when new rolls of tape are placed on the wrapping machine and then quickly resumed. The Company no longer uses over-the-ditch asphalt or coal-tar coatings, but has used them on lines in the past.