MIL STD 1627
Terms
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- Authorized Representative: Any Govermment representative specifically authorized to approve equipment, material, or procedures within the scope of this document for NAVSEA. They are as follows:
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(a) For Government shipyards: The delegated representative of the Shipyard Commander.
(b) For Commercial shipyards: The delegated representative of the Supervisor of Shipbuilding, Conversion and Repair (SUPSHIP), or the American Bureau of Shipping when specified in the Ship’s
Specifications for a particular ship. This includes all applicable areas in the shipyard and applicable items furnished to the shipyard by subcontractors.
(c) For Government purchase items: The delegated representative of the
Commanding Officer, NAVSSES, Philadelphia or of the Officer in Charge, NAVSSES Detachment, Mechanicsburg,or of the Officer In Charge, NAVSSES Detachment, Norfolk.
(d) When delegated by (a), (b) or (c) above, The representative of the Defense Contract Administration Services Management Area (DCASMA).
(e) Technical
representative specifically authorized by NAVSEA. - Backwall
- The outer half of the pipe or the half of the pipe undergoing tension during bending
- Bend Radius
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The radius from the center of Curvature to the center line
(axis) of the pipe, expressed as a number multiplied by the pipe or tube size.
For example, bend radius of a 5D bend for 2 nominal pipe size (rips)pipe or a 2
inch tube is 10 inches. - Bending Machines
- Equipment used to produce bends in pipe and tube.
- Bending machine - Ram type
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Ram type bending machine consists of a
bending die mounted on a ram and two pivoted pressure dies. The pipe is bent by
the bending die, pushing the pipe between the pressure dies, which wraps the pipe
around the bending die as shown on figure la. The bend in a ram type bending
machine is limited to 120 degrees and the bend radius should be not less than 6D. - Bendine machine - Roll type
- Roll type bending machine consist of three properly spaced rolls. The method of bending pipe by this machine is shown on figure lb. Bend angles of 360 degrees can be obtained on this type of bending machine with a minimum bend radius of approximately 6D on unfilled pipes,
- Bending machine - Compression type.
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The compression or stationary die type bending machine consists of a stationary bending die, clamping block, and movable pressure die. The pipe is bent by clamping one end of the pipe to the
bending die and the pressure die moves around the bending die, forcing the pipe into the bending die groove as shown on figure lc. The maximum angle of bend that can be produced is 180 degrees. - Bending machine - Rotary type.
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The rotary type machine consists of rotating bending die, clamping block, wiper die and sliding or stationary pressure die as shown on figure ld. The clamping block holds the end of the pipe to the bending die with sufficient force to keep it from moving while it is being bent around the die. The bending die rotates around a pivot and pulls or draws the
pipe around it. The bending die also supports the inner half or throat of the pipe bend. The pressure die presses the pipe into the groove of the bending die.
The pressure die also supports the outer half or heel of the pipe bend. The pressure die may be stationary or slide with the pipe. The wiper die is stationary and opposite the pressure dies. The wiper die supports the inner half of the pipe and keeps the pipe throat from wrinkling. The maximum angle of bend is 180 degrees. - Bending Machine - Rotary type with booster
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This machine is essentially the rotary type bending machine with the force being applied to the straight end of the pipe. This force reduces the pull on the pipe to bend it around the bending die as shown on figure le. Booster unit enables smaller radius
bends to be made on the pipe. - Buckles and bulges
- A wavy condition which may form on the pipe throat surface during the bending operation.
- Cold bending.
- The bending of pipe at any temperature at which strain hardening occurs.
- Crack
- A crevice, fissure, rupture, or fracture of the pipe surface.
- Dent
- A depression in the contour of the pipe surface.
- Flatness
- An area on the pipe surface having no curvature.
- Gouge
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A groove, cavity, or scooped out area on the pipe surface
produced by a sharp object or abrasive. - Hot Bending
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The bending of pipe at a temperature at which strain
hardening does not occur - Hump
- A rounded protrusion or bulge on the backwall or heel of the pipe bend caused by the improper placement of the bending mandrel.
- Minimum design thickness
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The wall thickness specified on the fabrication drawing or computed in accordance with the applicable shipbuilding
specification as the minimum acceptable for the temperature and pressure application,
whichever is greater, - Pipe
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The term “pipe†as used herein shall include both ‘pipe and
tube, in accordance with the nomenclature set forth by the material specification, - Qualified
- The item under consideration has been approved as required by this standard.
- Step
- A round buttoned crease on the throat of a pipe bend caused by the lack of, or improper spacing of the wiper die during the bending operation.
- Wrinkles
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Definite folds, or creases, formed on the surface of the
pipe during bending operations, - Material
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Base material shall conform to the applicable contract,
shipbuilding or equipment specifications. A list of generally used piping or
tubing materials, arranged in groups in accordance wfth similarities in bending,
are given in table I. - Base material condition
- Prior to bending, the base material in the vicinity of the bend shall be in the following conditions. The pipe is usually procured to these conditions and provided no cold work has been performed on them, no additional heat treatments are required.
- Base material cleanliness
- Prior to bending, the pipe surfaces, inside and outside, shall be clean and free of foreign matter which may result in nicks and gouge marks on the bent pipe surface.
- Wall thickness
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Pipe selected for bending shall have sufficient wall
thickness to assure that the backwall of the finished bend meets the minimum design thickness (Tin)or the minimum specified thickness. - Surface condition
- The surfaces to be bent shall have neither dents, nicks, nor gouges in excess of that permitted by this standard
- Lubricants
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Lubricants may be used in bending operations to prevent
galling of the pipe material during bending and to prevent rapid wear of the die.
Lubricants shall be easy to remove after bending and shall not stain the pipe. A lubricant that works effectively on one pipe material may not be effective for another. Mineral oils and organic fats, such as lanolin, are commonly used
lubricants. Examples of acceptable lubricants are lanolin, lard oil, viscous oils and soap solutions. Lubricant shall have good surface adhesion and film strength at bending temperatures. - Unacceptable lubricant ingredients
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(a) Qzona depleting lubricants not meeting local volatile compound (VOC) requirements shall not be used.
(b) Lubricants containing sulfur or chlorine shall not be used on group
S-8, S-31, S-32, S-34, S-42, and S-43 materials.
(c) Carbonaceous lubricants shall not be used on group S-8 materials.
(d) Iabricants containing halogens, arsenic, bismuth, copper, phosphorus, sulfur, tin, lead, cadmium or zinc in excess of 250 parts per million (ppm) total halides or 250 ppm of each other
individual element shall not be used on material intended for semice at temperatures greater than 400 degrees Fahrenheit (“F). - Cleaning
- Piping components and assemblies of components shall be thoroughly cleaned after fabrication and before installation in the ship to remove loose particles, grease, dirt, oil, rust, and scale.
- Loose fillers
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Loose fillers, such as silica sand and approved low melting material (such as rosin) may be employed for internal support when mandrels are not available or practicable. Low melting rosin, melting at temperatures not to exceed 400 degrees F, shall be used for bending at ambient temperature. Removal of rosin by direct torch heating shall be limited to 400 degrees F. Silica sand used for high temperature bending shall be dry. The sand should be 912 minimum silica, containing no nonferrous contaminants and having a fineness sufficient to yield a surface which meets specification requirements.
Sand previously used in nonferrous pipes shall not be used in ferrous pipes and
vice versa. - Material Controls: The following material controls shall be required:
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For corrosion resistant steel pipes: The silica sand used shall be clean and dry, and shall not be used for purposes other than filling corrosion resistant steel pipes. Hand tools that cow in contact with the corrosion resistant steel pipe shall be either
corrosion resistant steel or rust free ferrous tool steel and shall not be used on material other than corrosion resistant steel.
Resin shall not be used for pipe filling.
For carbon and alloy steel pipes: The silica sand shall be clean and dry and shall not be used for purposes other than filling ferrous pipes. Resin shall not be used for pipe filling, Galvanized parts, bronze or lead tools shall not be used or come in
contact with the pipe.
Nonferrous pipes: The silica sand shall be clean and dry and shall not be used for purposes other than filling nonferrous pipes.
Galvanized parts or lead tools shall not come in contact with the pipe. - Bending procedures
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Prior to performing production bending, each activity shall prepare detailed written bending procedures. Bending procedures shall be based on the requirements and acceptance criteria of this standard and shall include the following (see 6.2):
(a) Base material type, pipe size and wall thickness.
(b) Pre-bending preparations (see 4.1).
(c) Bend radius.
(d) Bending temperature (hot or cold).
(e) Type of bending machine (see 5.2.2).
(f) Type of lubricant, if any used (see 4.2).
(g) Bend angle adjustment where applicable.
(h) Out-of-round and buckling repair.
(i) Post bending heat treatment, if any.
(j) Post bending cleaning requirements.
(k) Inspection requirements and acceptance criteria. - Bending procedures - qualifications
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Bends to a radius of SD or greater for materials listed in table 1 do not require procedure qualification. When pipe is bent to a radius of less than 5D, each activi~ shall qualify procedures for each of the groups (a through e) listed below. Qualification of any material in a group qualifies for all materials within that group. Qualification of a bend to a
radius of less than SD qualifies for all bends intermediate to that radius and SD.
(a) Carbon and alloy steels - material groups S-1, S-3, S-4, S-5.
(b) Corrosion resistant alloys - material group S-8, S-42, S-43 (Inconel 600)
(c) Aluminum & aluminum alloys - material groups S-21, S-22.
(d) Copper alloys - material groups S-31, S-32, S-34.
(e) Nickel-chromium-molybdenum-columbium alloy - Inconel 625 material
group S-43.
NOTE 1: Aluminum alloy 5052 or 5086 qualifies the pipe bending of other alloys
in S-21 and S-22 groups and not vice versa. - Production bends as qualification test
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At the option of the activity, two production bends which represent the smallest radius bend for the system may be used for qualification tests. In this case, qualification applies to that particular size and wall thickness only; however, the qualification
applies to all material within that group.