What a process design package should contain
A design package is easy to fake. A layout drawing, a list of equipment and a few photographs of a similar plant look convincing in a quotation. Then the plant is built and the pipework does not fit, the foundation is 200 mm short, and the dryer cannot be changed without cutting the roof.
Six documents, in order
Every usable package contains the same six things. They are not optional extras and they are not interchangeable with a brochure.
| Document | The question it answers | What happens without it |
|---|---|---|
| Design basis | What must the plant do, with what raw material, at what site? | Every later argument is settled by memory or by whoever is louder |
| Mass and heat balance | How much of each stream, and how much steam, power and water? | Utilities are undersized, and the dryer becomes the bottleneck |
| PFD and P&ID | What connects to what, and how is it controlled? | Piping is guessed on site; instruments are added after the fact |
| General arrangement | Where does everything sit, and can it be maintained? | Equipment is installed, then found to be un-serviceable |
| Foundation loads | What must the civil contractor build? | Foundations are over- or under-designed; erection waits for rework |
| Equipment datasheets | What exactly is being bought? | The wrong machine arrives and the schedule absorbs the difference |
A package missing any one of these is a quotation, not a design.
Four questions that reveal the difference
You do not need to be a process engineer to test a supplier. Ask these four and listen to the shape of the answer.
- 01
Why is this pipe 80 mm and that one 50 mm?
A designer answers with a velocity and a flow rate. A reseller says it is standard.
- 02
How was the tower height chosen?
A designer talks about gas velocity, packing height and the outlet limit. Anyone else talks about the last project.
- 03
What is the foundation load at each anchor?
If the answer is a total weight with no anchor schedule, the civil design will be guesswork — and your concrete will be poured twice.
- 04
What revision is this drawing, and what changed?
A controlled drawing set has a register. An uncontrolled one has file names ending in final-final-2.
Why the cheap package is expensive
A package that stops at the layout saves the supplier perhaps three weeks of engineering. On site, those three weeks reappear as a piping rework, a re-poured foundation, an extra month of supervision and a commissioning period that never quite reaches design rate. The saving is real; it is simply paid by the client, later, in a currency that is harder to account for.
What to ask for
Ask for the drawing register of a similar project before you ask for a price. A supplier who cannot produce one has not produced the drawings. Ask for the revision status of two sheets, chosen at random. And ask who will answer a technical query during construction — a name, not a department.
If the answers are good, the price will be defensible. If they are vague, the price is not the number you should be comparing.