In chemical plants, we often need to estimate how much piping work is required. But instead of just measuring pipe length or weight, engineers use a special unit called DB, short for Dia-Inch.
DB makes it easier to estimate workload by combining pipe size and length into one value. This is especially helpful when comparing different pipe sizes or when making cost estimates.
In this article, we’ll explain what DB means, how it’s calculated, and why it’s useful in piping design and planning.
What Does “DB” Mean?
DB (Dia-Inch) is a unit that combines pipe diameter and length:
DB = Diameter (inches) × Length (inches)
For example:
- A 6-inch pipe, 100 inches long → DB = 6 × 100 = 600 DB
- A 2-inch pipe, 300 inches long → DB = 2 × 300 = 600 DB
This shows both pipes might require similar effort to install.
DB of Equipment Inside the Plant (Dia inch)
The piping around equipment inside the plant is also about 200 DB. The same approach as for outdoor tanks can be applied inside the plant.
Single Pipe: 40 DB
Let’s look at one pipe at a time, as in the outdoor tank example.
- 50A pipe: 40 DB
Pump suction, pump header, circulation, and pump discharge were all roughly 40 DB. Using the same idea, let’s consider one pipe as 40 DB.
Piping Between Equipment
Piping between equipment is assumed to be 50A, 5 meters long, and 10 DB. The approach is the same as the pump suction line example.
The concept for piping between equipment is “route the pipe through available space inside the plant.” We use 5 meters per pipe segment as a unit. The welding DB required for connections is as follows:
- Flange connection: 4 DB
- Welded connection: 2 DB
To route the pipe through plant space, elbows are needed to change direction. One 50A pipe typically has 3 elbows:
- Flange connection 4 + route change 2 × 3 = 10 DB
Connection Nozzles
Each piece of equipment has a limit on the number of connection nozzles. Here, assume 8 nozzles. If each nozzle has one pipe connected, using the calculation above:
40 + 10 = 50 DB
For equipment with 8 nozzles:
50 × 8 = 400 DB
This value can be considered the minimum piping DB for a piece of equipment. More complex cases exist in reality, but these can be corrected later.
DB of Batch Chemical Plant Equipment
Minimum 400 DB
DB for One Process
In batch chemical plants, one process usually has about 2,000 DB. Let’s explain the approach.
Equipment in One Process
A typical process in a batch chemical plant has about 5 pieces of equipment. Standard equipment includes tanks, heat exchangers, and pumps, giving a total of 3 units.
For distillation, heat exchangers may increase to 2, and receiving tanks may add 1–4 units. The minimum is 3, maximum 8 (3 + 1 + 4), so 5 pieces of equipment per process is a reasonable summary.
Summary Calculation
One tank: 400 DB
5 pieces of equipment per process: 400 × 5 = 2,000 DB
DB per Process in a Batch Chemical Plant
Minimum 2,000 DB
DB for One Plant
A batch chemical plant has roughly 20,000–40,000 DB. Following the calculations above, the logic is simple. There are about 10–20 processes.
Reactions
In a batch chemical plant, the maximum number of reactions is about 5, averaging 3. Including pre- and post-processing, there are about 9 processes at the process level.
Filtration and Drying
If there are special units like filtration or drying, each can be considered as one process: 1 process for filtration, 1 for drying.
Other Equipment
Other equipment in batch chemical plants includes:
- Filters
- Hoppers
- Storage tanks
- Heat exchangers
Each has few connection pipes, but accumulated they may equal 2–10 processes. This number can vary significantly.
Summary Calculation
- 1 process: 2,000 DB
- 1 plant: 10–20 processes
- Total: 2,000 × 10–20 = 20,000–40,000 DB
The variation depends on the characteristics of the plant.
DB and Plant Construction Costs
We can roughly estimate plant construction costs from DB. This is mostly a numerical approximation.
Construction Cost
Building one batch chemical plant costs about 4 billion yen as a rough estimate. If you include material, labor, and other expenses, piping construction for 40,000 DB is about 400 million yen. This is far below the total 4 billion yen.
The 4 billion yen includes machinery, electrical, instrumentation, civil engineering, and other fields. Mechanical work alone is about 1.2 billion yen, with piping work alone about 800 million yen.
Thus, at plant construction level, DB alone cannot fully determine costs. Factors like the number of outdoor tanks, piping between tanks and the plant, and utility piping all add at least 100 million yen. Additional auxiliary equipment also adds cost.
- Piping construction: 400 million yen + auxiliary piping: 100 million yen = 500 million yen①
- 4 billion yen / 5 = 800 million yen②
500 million yen① < 800 million yen②
Even rough calculation gives reasonably accurate insight. Budget estimation using DB can be done this way.
Expansion and Renovation
Adding new products or modifying an existing plant usually costs about 1 billion yen.
If costs are higher, it may no longer be a worthwhile investment. This is about 1/4 of the cost of a new plant, corresponding roughly to 10,000 DB, which aligns well with practical experience.
Common Mistakes or Misunderstandings
Some beginners confuse DB with weight or material cost. But DB is not about physical mass — it’s a workload estimate tool.
Also, remember that DB doesn’t consider complex shapes like elbows or tees. For detailed work, you may need other unit-based estimates too.
Summary
DB (Dia-Inch) is a useful unit in chemical plant design to estimate piping workload. It reflects both size and length of pipes, helping engineers and managers plan better.
While it doesn’t cover everything, it’s a fast and practical way to compare tasks and costs, especially in the early stages of a project.
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