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Front End Change is Required
When Designing for Constructability
By: Walter J. Boyce
INTRODUCTION
Change is absolutely essential
for progress. Without change we keep building the same
old things to the same old standards, which is the very
definition of No Progress. The change must be at the front-end
of the project, during the conception phase. Changes after
the conception phase and during the execution phase will
be disruptive rather than constructive to the project.
Open minds are also essential for change; closed minds
do not accept change. An open mind found that the world
is round; the closed minds said he's going to fall off
the edge of the world. Change also requires a strong project
management team with a project manager that has an executive
role.
"Project management and brain surgeons should not
be selected on the basis of the lowest bid."
- Author Unknown
The executive role of the project manager is also essential,
as a project manager (so called) in a monitoring role
cannot make exceptions to the old corporate standards,
even when substantial savings could be realized. Change
should not compromise quality or safety; but again, "No
Change" means "No Progress."
"The executive exists to make sensible exceptions
to general rules."
- Elting E. Morison
Body
Designing for Constructability
is really just updating old engineering standards, specifications
and procedures. Most of these were developed years ago
when the building materials were expensive and manpower
was less expensive. These antiquated practices are costing
companies, both owners and contractors, a lot of money
on every project. This money doesn't benefit either owner
or contractor; it goes right down the drain. When you
hear, "We've always done it this way," you can
be sure of obsolescence.
"To meet the demands of the fast changing competitive
scene, we must simply learn to love change as much as
we have hated it in the past."
- Tom Peters
Paradigms are very hard to overcome, but change doesn't
happen until we do. Some concepts of Designing for Constructability
follow.
1. Straight pipe is not expensive—
fittings, valves, flanges and changes in direction
are.
2 Run pipeways first, not pipes — run pipeways
vertically as well as horizontally.
3. Use large process nozzles for infrequent vessel
entry and eliminate manways. When the process nozzle
is not quite large enough, use a reducing flange.
4. Use manways and large nozzles for lifting lugs.
Manways can also be used for several process connections.
5. A 24" manway costs about twice the cost of
an 18" manway.
6. Try to keep equipment close to the main piperack
so that additional supports are not required.
7. Try to keep all equipment connections on the side
of the piperack to facilitate pipe access to the piperack.
8. Support and anchor items and piping as close to
the ground as possible. Skirt mounting the vertical
vessels and saddles that extend to the mat foundation
for the horizontal vessels are part of this concept.
9. Low, level piperacks are less expensive —
when safety permits, field installation, insulation,
painting, testing and inspection are all about half
the field cost of high level rack piping, which requires
the use of scaffolding.
10. Piperack design can be a big factor in the cost,
schedule, and layout when a major piperack is required.
11. Compressors should share lube oil and seal oil
units. This concept was recommended by the operations
and maintenance people of an existing plant who had
four compressors with eight oil units (four seal oil
and four lube oil units). The plant would not run
without all of the compressors, and that meant that
all eight of the oil units must also be in operation.
That was a total of twelve units, any one of which
would shut the complete plant down. Their recommendation
was to design with one highly reliable oil unit. They
had found one oil that was suitable for all the compressors
and they were using the same oil in all eight units.
12. Centrifugal compressors can often be mounted on
vibration insulators with no anchor bolts. This simplifies
the foundation and reduces the noise of operation.
13. A furnace stack was designed with a jacket and
no refractory. The jacket space was used to preheat
air. Corrosion must be considered.
14. All instrumentation and gas piping was designed
to go through the catwalks of a large furnace. The
openings for these items were omitted from the grating
drawings, and the field extra was about a half million
dollars. The next project was designed to have these
items next to, and not through, the catwalks.
15. Heat exchangers and also horizontal drums can
be supported with saddle supports that extend down
to the mat-type foundation. This eliminates the second
activity of pouring two concrete piers. The supports
can be further simplified by having one of the saddles
designed as the rigid anchor support. The other end
saddle is designed to flex and eliminates the need
for slotted holes and slide plates. When trying to
maximize shop fabrication, these saddles can be used
to support piping, instrumentation, etc. so that when
the item is set on the mat-type foundation, the field
man-hours are less.
16. Small, miscellaneous custom designed platforms,
ladders, and stairs are expensive, particularly curved
platforms — they are estimated at 2 1/2 times
the cost of rectangular platforms (on a per square
foot basis).
17. The major equipment is about 25-percent of the
total installed cost of a project. The remaining 75-percent
is the main target area for the Designing for Constructability
savings.
18. Structures, when required, should be utilized
to the fullest extent possible, and minor items can
be brought to that structure rather than building
a new structure.
19. Small concrete piers, pads, and paving pours are
expensive ($700 per yard) when compared to mass pours
of about $100 per yard (today's basis).
20. Buy standard equipment using a performance type
specification. Select vendor and negotiate minor changes,
the delivery, and the spare parts (for years).
A study of standard specifications for a major E &
C contractor found much duplicate information —
and, as would be expected, where information is repeated
time and again there is also conflicting information.
Eliminating the duplicate information reduced the
thickness of these specifications to one fourth of
the original thickness. The following chart shows
the equipment classifications and subjects covered.
Everything below the top line of "x's" is
redundant but not identical. The solution is to have
a cover specification to cover all the co-on subjects
once and not have them repeated in each equipment
specification because that would be a big expense
in duplication and confusion.
The updating of engineering,
standards, specifications and procedures should follow
the Ten Commandments of the KISS Philosophy:
KEEP IT STRAIGHT&
SIMPLE
KEEP IT SAME SIZE
KEEP IT SHOP STANDARD
KEEP IT SQUARE & SQUATTY
KEEP IT SPECIFICATION SIMPLE
KEEP IT STANDARD SIZE
KEEP IT SUPPORT SIMPLE
KEEP IT STANDARDS SIMPLE
KEEP IT SCHEDULE SACRED
KEEP IT SUITABLE FOR SITE
Keep it Straight & Simple …
applies to many things but is most
important when doing the plant layout, starting with piperacks,
roads, sewers, cable trays and drainage ditches.
Layout of the equipment required for a project is a very
important aspect of Designing for Constructability. Accessibility
may be the best word to define layout: Access for people,
equipment, piping, electrical and instrumentation. The
access must consider construction, production, safety
and maintenance. The layout must be finalized early in
the project but is often not given the proper attention
it requires. There is probably no one item that can influence
the cost more than the layout.
There are many ways to make a layout. I feel that the
best and fastest way is with a simple block model. No
drawings are made to make the model: the model comes first,
the drawings come second. A model is not only three dimensional,
it also speaks all languages — not just foreign languages
but the languages of construction, production, safety,
maintenance, etc. With the simple block model we lay out
pipe racks, cable trays, drainage ditches, roads and buildings
first; then place equipment. This will make a cleaner,
straighter and less expensive layout. Don't locate a piece
of equipment without knowing how you are going to get
to it with pipe, electrical, instrumentation, etc. Don't
run pipe racks and roads side by side as this will sterilize
one side of the rack as far as equipment placement is
concerned. This will often force spur pipe racks to be
required, which in turn require at least two bore pipe
fittings and additional pipe to reach the equipment. This
also adds to the total length of pipe rack required, and
total cost is function of length.
Keep it Same Size …
includes things like heat
exchanger tubes and support spacing, vessel manways and
instrument connections, pipe rack supports, building bays,
control valves and block valves, windows, doors, etc.
Keep It Shop Standard …
is a big factor of cost.
When supplier is asked to deviate from his standard, it
will cost more. It will be a custom order; it will probably
take longer and it may carry lesser guarantee since it
is not his proven standard. He is not likely to tell his
client this as he is bending over backwards to satisfy.
Keep It Square & Squatty …
applies to many things, including
buildings, as a square building is less cost per square
foot than T-shaped or L-shaped building. The "Squatty"
is to stress the cost of building structures and equipment
higher than necessary. This is even more important in
earthquake areas.
How high does the structure really need to be? NPSH requirements
are, of course, a real concern — but contingencies
on top of contingencies have been found to add considerable
cost to structures and to the whole total installed cost.
The real situation may have the normal liquid level several
feet above the outlet, which should be
considered. The unreal custom of calculating NPSH requirements
based on full design flow (plus more contingencies) at
the face of the vessel outlet flange is part of the problem.
A review of the above, plus other contingencies, resulted
in lowering a complete process unit by l§
feet. This involved some open-minded process people.
Keep It Specification Simple …
so that the shop standard equipment
can be purchased. The simple specification would be a
blue Cadillac with four doors and loaded with standard
Cadillac extras while a complex specification would be something like a red Honda with a Chrysler motor, a Ford transmission and a Rolls Royce radio. This sounds ridiculous, but a lot of companies are buying this type of equipment.
Again, the vendor is not likely to tell his client about
this as he is trying to satisfy.
Keep It Standard Size …
applies to many items. Foundations
and concrete structures can be designed to fit standard
size forms. Vessels can often be designed to fit standard
size steel plates. Standard size vessels can often be
bought from a catalogue. These are pre-engineered and
generally involve less cost and quick delivery. They can
be purchased with jackets, agitators, etc. Standard size
for a project need not be an industry standard. The project
can set its own standards for many things to simplify
constructability, such as manway size, instrument supports,
handrails, stairs, ladders, anchor bolts, etc.
Keep It Support Simple …
which starts with a mat-type foundation
for a process unit. As many items as possible are designed
to sit on the mat. Vertical drums are preferred as they
require less space and can be skirt or leg mounted on
the mat without the additional activity of piers, etc.
Vertical reboilers can also be on legs. Inline pumps are
much simpler to support and are less total installed cost.
Heat exchangers and horizontal drums can be designed with
one support rigid and one support flexible in lieu of
slotted holes and slide plates. The pipe rack design concept
(which follows) makes a lot of custom supports unnecessary.
Keep It Schedule Sacred …
as the financing, payback and product
sales contracts are all based on the start-up date. The
schedule must be realistic and Designing for Constructability
should shorten the schedule. Once a realistic schedule
is developed, stay with it and do what is necessary to
make it happen.
Keep It Suitable For Site …
location, as local conditions change
as to wind, sun, rain, temperature, labor supply, customs,
available materials and equipment. These factors should
have an impact on the design, procurement and construction
approach.
Keep It Standards Simple …
is the real key to Designing for
Constructability. Concepts for standardized pipe racks,
stairs, handrails, storage tanks, compressor structures,
access platforms, block valves, flare headers, cooling
tower and control building design follow.
Pipe Racks …
are a major item in most process
plant projects. They are substantial structures and
often fireproofed. They can also be used to support
some equipment that requires elevation. This concept
is based on a precast concrete rack design which is
wider, but with outriggers to minimize span and with
a precast concrete deck on top. This design may require
more ground area but gives an equal amount of prime
space on top of the deck right in the center of the
process. In theory (and in fact) this has shortened
the overall length of the rack layout by one-third,
because in addition to the two sides of the rack, we
can now use three sides of the rack, including the top.
This pipe rack concept has many advantages:
1. Cost and schedule are both improved.
2. Gives a liberal maintenance access way under the
center of the pipe rack between the support columns,
±14 feet heath.
3. Outside of the support columns the outriggers give
extra rack space and uses space down to ±8 feet
high.
4. The top precast deck gives weather protection and
improved productivity for construction, production and
maintenance.
5. The deck is also a firebreak between the piping and
the equipment on top.
6. With this wide area of access, exchanger bundles
can be pulled into this covered area. With the dirty
end of exchangers towards the pipe rack, the piping
is shortened and the oily water sewer is in a straight
line.
7. The precast deck can be used for many elevated items.
This has also eliminated many structures alongside of
racks, which also impede access to the rack. The piping
to items on top of the deck are generally shorter.
8. The deck which covers the full width and length of
the rack in the process area also serves to support
any pipe entering or leaving the rack, by rod hangers.
9. The deck also serves for access to control valve
stations and often shortens the piping which would otherwise
go down to grade and up again. Relief valve stations
are also mounted on this deck; and with the flare header
Just below the deck, the relief valve discharge piping
is short.
Stairs …
fabrication is greatly simplified.
When all operating and maintenance floors, platforms,
catwalks, stairway landings, etc. are established at
L-we-foot increments, it will make all stairways the
same angle with 8" risers and 10" treads.
Three risers and two ladder rungs will equal two feet.
The two foot increments must apply to the top of the
walking surfaces. This not only makes the stair stringers
the same angle, but also the handrails, etc. It simplifies
design, fabrication and construction.
Handrail …
fabrication is simplified with
standard bays, and handrail design can also be simplified
compared to many standards. One design, which was used
to simplify field fabrication made necessary by local
labor requirements, proved to be very cost effective.
This design was further simplified by having all operating
levels on the two-foot increments, as discussed above,
so that all stairway handrails were the same angle,
then standard bays can be utilized, 20-foot bays would
have two ±9'-2' sections and 24-foot bays would
have three 7'-4" sections.
Compressor Structures …
requiring cranes can be designed with an "A"
frame type crane supported on the concrete tabletop
which supports the compressor. This will make a second
structure to support a bridge crane unnecessary. Cantilevered
extensions from the tabletop will support precast concrete
decking on both sides of the compressors. A pre-engineered
building can be added to the tabletop to give weather
protection.
Storage Tanks …
can often use standard plates
to minimize cutting and waste. A tank fabricator required
a very high cancellation fee when tanks were canceled
because he had cut the plates and considered them to
be of little value. It seems that standard tanks are
not even-feet in diameter but even-feet in circumference.
His plates were 84 inches by 240 inches, or 7 feet by
20 feet. His standard tanks had diameters of 6.37 feet
(one plate), 12.74 feet (two places), 19.1 feet (three
plates), etc.
Access Platforms …
are determined to a great extent
by nozzle locations. Random nozzle orientation can be
very costly. One project found that planned orientation
of nozzles reduced the amount of platform required
by about half. The contractor on that project had a factor of
2h times the cost of rectangular for the cost
of circular ones. With the planned orientation of nozzles,
most of the platforms were rectangular. Each vessel
needs to be reviewed by open-minded process, piping
and vessel people to accomplish these substantial savings.
Block Valve Sizing …
for control valves, pumps, traps
and relief valves can not only be a very big dollar
item, but also a substantial manpower factor.
Control valve stations can be treated as a sub-assembly.
They can be shipped complete  with
the control valve positioned above its working position
held in place by through bolts which also hold a straight
piece of pipe between the matching flanges of the block
valves. The straight piece of pipe (no flanges) is used
for flushing and testing, then discarded and the control
valve lowered into place.
To make this concept work there two sizes required:
the line size and the control valve body size. The line
size is usually the first to be known and often the
block valves are ordered on this basis. This practice
can be very costly, particularly when the control valve
body size is more than one size smaller than the line
size. The trim size of the control valve can be known
later. Once the two sizes are known, the block valves,
the bypass valve, the reducing ells and the flanges
can be purchased. The valve bodies will all be the same
size. The control valve will have trim with an orifice
about 2/3 to 3/4 of the valve body size. This gives
an area of about half the cross section of a full port
block valve of the same body size. (One client called
the pressure drop through the block valves negligible
after their computer check.) In addition to saving valve
costs, there are additional savings in the field installation
ape— and gear operators can often be eliminated
with a smaller block valve size. The bypass valves could
be sized based on the control valve trim capacity; this
would usually be a smaller body size than the control
valve size.
This concept requires only half the welds of the standards
which call for block valves to be smaller than line
size, but bigger than control valve body size. Notice
that reducing cells are used to go from line size to
valve body size. Buying an ell and a reducer in lieu
of one reducing ell and then making three welds in lieu
of two welds is not Designing for Constructability.
FLARE HEADERS ...
are often designed with supports
spaced every 20 feet and a conventional, narrow rack
with two footers -and two vertical supports. Designing
for Constructability has utilized the structural strength
of the flare header to support the small lines and conduits
or cable tray every 20 feet, but the flare header supports
can be much farther apart. Designs have used 60-foot
spacing for 36" headers and 100-foot spacing for
72-inch headers. This reduces the number of footers and
structural columns to one-sixth or one-tenth the number
required at 20-foot spacing. These items will be bigger
but should require a lot less cost and time.
COOLING TOWER ...
piping is simplified when
basin and pumps are on a common mat foundation. When
the pump suction lines are short they should not require
a size any bigger than the pump suction size. The pump
basin can be Just an extension of the tower basin. When
the screens are installed at an angle, the extension
is minimal. Man-hours in forming can be minimized when
concrete piers are eliminated in lieu of longer columns
of the cooling tower structure; also man-hours can be
saved by making the mat foundation thicker and all in
one piece. When the basin and pumps are on a common
at-type foundation and there can be no differential
settlement, then expensive expansion Joints in the pump
suction piping can be eliminated.
CONTROL BUILDING DESIGN ...
can be simplified to reduce both
man-hours and cost. Some of the concepts to look at
for simplification follows.
The instrument racks can be connected and fed from the
top in lieu of the bottom. This eliminates the need
for the computer floor in the rack room and shortens
the wiring as they enter the building near the top of
the racks.
The control room is located directly above the rack
room. This eliminates the need for the computer floor
in the control room as penetrations can be made in the
floor where required. Again this shortens the wiring.
The ground floor would have, in addition to the rack
room, the locker rooms and the main toilet facilities,
the mechanical room and switch gear room.
The second floor would have the cleaner functions. In
addition to the control room there would be the offices,
the laboratory, conference room and more toilets. There
are both advantages and disadvantages of this second
story concept. I feel that the main advantages are the
smaller foundation, simplified air conditioning and
simplified construction.
Simplified construction of this building can reduce
field man-hours substantially. The use of precast double
"TT's" for second floor, roof and exterior
walls makes for fast low-cost shell. This is an acceptable
"blast resistant" building. This type of construction
can also eliminate the false ceilings and simplify the
lighting and air conditioning. I call this "parking
garage construction".
Lighting is by fluorescent single bulb units mounted
directly on the underside of the double "TT decking".
This also covers most of the Joint between the sections
of decking. The conduit and Junction boxes are on the
top side of the double "TT's" and then buried
in the lightweight concrete floor and roof. The telephone
conduits are also buried like this. The junction boxes
are flush with the finished floor and accessible.
Air conditioning ducts are large rectangular soffit-type
design. They may be on one wall or all four walls, depending
on the size of the rooms. The distribution is controlled
by outlet dampers rather than duct size. One client
opted for thermostat controlled dampers so that two
offices side-by-side could have several degrees differential
to suit the comfort of individuals.
A Middle East project had 12 air conditioning units
in as many areas throughout the complex. They also used
a substantial amount of chilled water in the processes.
We had three 50% chilled water units from which we used
chilled water as a utility to air handling units at
the 12 locations. This not only eliminated the 12 A.C.
compressors, but also the noise in office-type areas
and the maintenance of the compressors.
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