Following are questions which have been asked of us over the
years by prospective clients. Most of the questions are related to 1½D Close Radius Pipe
Bending and Lap Joint Flaring. APEX Piping Systems Specifications ES-7 and ES-8 should be
consulted when reviewing these FAQs
·
1½D Close Radius Pipe Bends:
1. How does the quality of 1½D Close Radius Pipe
Bends relate to welded fittings?
Answer: The following factors go into producing high quality 1½D pipe bends in which
wall thinning is held to a maximum of 18% of the actual pipe wall, Out of Roundness shall
not exceed 5%, and where minimal wrinkling is evident on the inside of the bend:
1. The pipe material which we use is of the highest quality and is a "Full
Finished / Bending Quality" material. We specify A-587 ERW for Carbon Steel, and
A-312 Types 304/304L and 316/316L material which meets DuPont Standard SW41M where the
material is manufactured and available. When using other materials, proper selection of
material to be bent is important.
2. The pipe is totally encapsulated in tooling.
3. The tooling is high quality, and well maintained.
4. The benders which we use are outfitted with Hydraulic Boosters which help produce a
better quality of bend.
The end result is a bend that is visually as appealing as a weld fitting manufactured
to ANSI B16.9. The noticeable difference is the elimination of the two (2) butt welds on
the bent piece. The wall thickness of a Factory- Made Wrought Steel Buttweld elbow fitting
shall be not less than 87.5% of the nominal thickness. Out of Roundness for an elbow
fitting in pipe sizes 4" and smaller can range from a maximum of 2½% to 10½%
depending on pipe size.
2. What is the typical amount of outer fiber wall
thinning?
Answer: The maximum wall thinning for 1½D bends to 90° is 18%. It is measured by the
difference between the actual thickness of the pipe, and the minimum thickness on the
outside of the bend. The Hydraulic Boosted bending process described above helps to
minimize the amount of wall thinning.
The "typical" wall thinning which we experience depends on size, schedule,
and material type. A historical review of the APEX Piping Systems "Bender
Set-Up" log book and our experience is that wall thinning of a 1½D bend usually runs
between 14% to 16%. Once a bender is set up, there usually is little deviation from these
results, and all bends are visually inspected as part of our in-process QC program. APEX
Piping Systems will also develop a specific QC inspection procedure for our clients if
they would require it on a project.
3. Are bends done hot or cold?
Answer: All 1½D pipe bends in Carbon and Stainless Steel are cold formed.
4. If cold, does plastic strain damage
mechanical properties or corrosion resistance?
Answer: The stress intensification factor for pipe bends is equal
to that for an elbow fitting. As a general rule the amount of stress or corrosion cracking
experienced from bending is similar to that produced by a butt weld. Therefore, if you are
required based upon the service to anneal the welds, you should also anneal the bends.
This is also assuming that the material selected is correct for the service conditions.
5. Are any post-fabrication heat treatments
required?
Answer: Post-Bend heat treatment is not normally required. However, the type of service
may require heat treatment.
· "Van Stone"
or "Lap Joint" Flaring:
1. What are the pressure / temperature ratings of
flared lap joints?
Answer: Flared laps are not to be used with 400# or higher rated back up flanges. A
flared lap is suitable for Normal Fluid Service per paragraph 306.4.2 of ASME B31.3.
2. Are the lap joints allowed "by
code"?
Answer: As stated above, flared laps are allowed per ASME B31.3, paragraph 306.4.2 for
Normal Fluid Service.
3. Are Flared Laps a Type "A",
"B", or "C"?
Answer: The designation of a stub-end being a Type "A", "B", or
"C" relates to how the fitting is manufactured, dimension of the fitting, and
the type of back up flange used. Following is a description of all three (3) types:
Type "A" - For use with Lap Joint Flanges. Manufactured by either being
forged and machined, machined from bar, or by welding a ring on the end of a piece of pipe
and machined to the final dimension. Type "A" stub ends have a square inside
corner, and a radius behind the lap, hence the need to use a lap joint flange as a back
up.
Type "B" - Manufactured in the same general manner as a Type "A",
but the Type "B" does not have a radius behind the lap. The back face is
machined square, thus requiring a Slip-On flange as the back up.
Type "C" - Same general dimensions of both a Type "A" and
"B" stub end. This fitting is manufactured by inserting the end of a piece of
pipe into a flanging machine and roll forming the end of the piece of pipe to form a ring
perpendicular to the pipe axis. The forming operation will leave a rounded edge at the
I.D. of the lap as well as a short fillet radius behind the lap. Back up flanges can be
either Lap Joint, Chamfered Slip- on, or plate flange.
APEX Piping Systems, in addition to forming these laps onto the ends of pipe lengths to
form bent and flared piping systems, is a commercial manufacturer of Type "C"
stub ends.
We might also add that if your company has specified the use of any
Teflon™ lined carbon steel pipe and fittings over the years, flared laps have been
used quite frequently by many of the manufacturers in this industry for their pipe spools,
and flanged fittings which they market. (90° elbows with the rotating back up flanges are
very popular).
4. How are they made? Do
techniques vary shop-to-shop? Do we have to qualify the flaring process to assure adequate
quality for the lap?
Answer: There are several different manufactures of flanging equipment available to
perform this specific operation. This process was developed in the mid-1960's as part of
an in-house project by the E.I. DuPont de Nemours and Company in an effort to reduce pipe
fabrication and plant construction costs. The rolling process to manufacture a flared lap
is generally the same, regardless of the equipment manufacturer. Some manufacturers of
commercial Type "C" stub ends are using equipment which forms the lap by using a
press operation. On fabricated piping projects, flared laps are 100% visually inspected as
part of the normal in-process inspections. Go/ No Go gauges can also be used to check
dimensional conformance. Other N.D.E. (such as Dye Penetrant) of the flared lap can be
performed if desired by the client.
·
Metallurgical Effects of Lap
Joint Flaring:
1. Are flared laps done hot or cold?
Answer: Most flared laps are cold formed, however in some cases the pipe schedule and
material type requires that the flared lap is hot formed. As a general rule, A587 Carbon
Steel, most Stainless Steels, and High Alloy materials are cold formed. A53 and A106
Grades of Carbon Steel are hot formed.
2. If cold flared, does plastic strain damage
mechanical properties or corrosion resistance?
Answer: The flaring operation is a more severe fabrication operation than bending. Some
of the factors that go into the production of high quality pipe bends, also should be
followed in the production of flared laps. Tooling should be of high quality and well
maintained. Of greater importance, is the need to procure pipe material which is of a high
quality. This also assumes that the material selected is correct for the service
conditions.
3. Are any post-fabrication heat treatments required?
Answer: Heat treatment of flared laps is not normally required.
4. Do we want serrated gasket surfaces?
Answer: In most cases flared laps for fabricated piping projects are provided with a
smooth face. The serrated finishes provided by APEX Piping Systems on flared laps is more
applicable to commercial Type "C" stub ends than on elaborate piping assemblies
due to additional handling requirements.
· Commercial
Issues:
1. Who uses high quality bends and lap joint
flaring in lieu of conventional fabrication techniques?
Many manufacturers within the Chemical and Fluid Processing Industries have
incorporated the use of both flaring and bending into their engineering standards.
Following is a partial list of some manufacturers:
DuPont Monsanto Rohm & Haas
Union Carbide Dow Chemical Hercules, Inc.
Bayer Procter & Gamble PPG Industries
Amoco Merck & Co. Johnson Wax
2. Who makes high quality bends and lap joints?
Answer: APEX Piping Systems is a leading manufacturer and shop
fabricator of piping who has the capability to perform both close radius bending and
flaring of pipe.
3. Is the A587 carbon steel
grade readily available?
Answer: Yes, A587 is readily available from several producers, both domestic and
foreign.
· Design Considerations:
1. Shall we use 1½D radius bends exclusively to
make piping design dimensions exactly the same as for normal long radius fittings? Or
should we consider longer radius bends, e.g. 3D, in an attempt to use more standard
materials ?
Answer: APEX Piping Systems routinely works from design drawings in which long radius
weld fittings are specified, and in which bending has been substituted. The secret to
maximizing the cost effectiveness of a bent and flared piping system is to follow the
minimum forming dimensions shown on page 4 of our specification ES-7. The APEX Piping
Systems Sales and Engineering departments are available to assist you in design of your
bent and flared piping system
The use of 3D pipe bends will require additional design considerations.
2. Do we really eliminate enough welds to
realize significant savings? Are the favorable cost considerations of a bent & flared
piping system negated by the need for field welds to adjust for field tolerance problems,
wall & floor penetrations or shipping limitations?
Answer: The favorable cost consideration of a shop fabricated bent
and flaredpiping system should be compared to a shop fabricated
conventional welded piping system only.
In either case above, decisions will have to be made with respect to location of field
welds, and wall & floor penetrations. The normal shipping envelope for all shop
fabricated piping is 40' X 8' X 8'.
It is also important to remember that you are not only
eliminating two (2) butt welds, but you are eliminating other labor operations, (such as
pipe cuts, and bevels) but also the purchase of the elbow fitting, and additional N.D.E.
such as Radiography.
3. What are the benefits of
shop fabrication over field fabrication?
Answer: It has been proven that shop fabrication of piping is
infinitely more cost effective than field fabrication. In addition, shop conditions also
lead to a much higher quality of fabrication as opposed to field fabrication due to the
fact that all conditions can be controlled, and better equipment and weld processes are
available.
4. What are the cost savings
associated with using a bent & flared system relative to welded fittings in Carbon
Steel? How about in Stainless Steel?
Answer: The cost savings associated with using a bent and flared system vs. a
conventionally welded system will be greater in the stainless steel, and high alloy
projects as compared to a carbon steel project. The cost savings will not only be evident
on the labor side, but should also be evident on the material side through the elimination
of fittings. Generally, we have experienced cost savings of 20 to 40% when comparing a
bent and flared system to a conventional system.
