How I use RISA-3D to model equipment platform loads from a P&ID

P&IDs contain the structural loads you need. You just have to know how to extract them.

After 6 years designing pipe racks and equipment platforms in oil & gas, I've learned that the most critical step happens before you even open RISA-3D. You need to decode the P&ID properly. Miss a pump or underestimate a vessel load, and your platform design fails.

Here's my workflow for turning P&ID symbols into accurate structural models.

Step 1: Create your equipment inventory

I start with a spreadsheet. Every piece of equipment gets catalogued:

Tag Number	Equipment Type	Operating Weight (lbs)	Dimensions (ft)	Elevation
P-101A/B	Centrifugal Pump	2,400	6 x 3 x 4	El. 115'-0"
V-201	Separator Vessel	18,500	12 dia x 25	El. 120'-0"
E-301	Heat Exchanger	8,200	4 x 12 x 6	El. 118'-0"

The P&ID shows you what's there. Equipment data sheets give you the weights. Don't guess these numbers. I've seen platforms fail because someone estimated a 15,000 lb vessel at 10,000 lbs.

Step 2: Identify load paths

Equipment doesn't float. Every piece needs structural support. I trace each load path from equipment to foundation:

• Direct bearing: Heavy vessels typically bear directly on steel beams
• Vibrating equipment: Pumps and compressors need isolation springs
• Piping loads: Large bore piping creates significant lateral forces
• Maintenance access: Platforms need live load capacity for personnel and lifting equipment

Your P&ID won't show you this. You need to visualize the 3D arrangement.

Step 3: Set up the RISA-3D model

I build my platform model in this sequence:

1. Create main structural grid
2. Define beam sections (W12x40 typical for equipment beams)
3. Add columns and bracing
4. Apply boundary conditions
5. Define load combinations per AISC 360

For equipment platforms, I use these typical member sizes as starting points:

• Equipment beams: W12x40 minimum
• Framing beams: W10x26
• Columns: W8x35 or HSS12x12x1/2
• Bracing: HSS6x6x5/16

Step 4: Apply equipment loads

This is where the P&ID analysis pays off. In RISA-3D, I model equipment loads as point loads with these considerations:

Static loads (Dead Load):

Equipment operating weight + piping + insulation + misc. steel
Factor: 1.2 (LRFD)

Dynamic loads (Live Load):

Maintenance personnel: 125 psf
Equipment removal: 1.5 x equipment weight
Piping expansion forces: from stress analysis

For the separator vessel example above:

• Dead load: 18,500 lbs operating + 2,000 lbs piping = 20,500 lbs
• Live load: 27,750 lbs for removal case (1.5 x 18,500)

I apply these as nodal loads in RISA-3D at the actual equipment support points.

Step 5: Model piping restraint loads

P&IDs show pipe routing but not restraint loads. You need to coordinate with the piping stress engineer. I typically see these magnitudes:

• Anchor loads: 5,000 to 50,000 lbs depending on line size and pressure
• Guide loads: 1,000 to 10,000 lbs lateral
• Spring hanger loads: Variable based on supported pipe weight

In RISA-3D, I model these as applied loads at beam locations where pipe supports attach.

Step 6: Check your work

Before running analysis, I verify:

• Total platform dead load matches equipment inventory ± 10%
• Load paths are continuous to foundations
• All equipment has adequate support points
• Live load combinations include maintenance scenarios

Common mistakes I catch here:

• Forgetting piping loads (can be 30% of total load)
• Underestimating access platform requirements
• Missing thermal expansion effects

Step 7: Analyze and iterate

RISA-3D gives you member utilization ratios. For equipment platforms, I target:

• Beams: 85% maximum utilization
• Columns: 80% maximum utilization
• Deflections: L/240 for equipment beams

If members are overstressed, I resize and reanalyze. The P&ID constraints are fixed. Your structure must accommodate them.

Real project example

Last month I designed a platform for three centrifugal pumps. The P&ID showed simple pump symbols. The reality:

• Each pump: 3,200 lbs + 1,800 lbs piping
• Suction/discharge forces: 8,500 lbs combined
• Maintenance crane load: 12,000 lbs
• Platform size: 20' x 30'

Total design load: 67,000 lbs on a platform that would carry 15,000 lbs if I'd only considered pump weights.

Your next step

Start with your current project P&ID. List every piece of equipment. Get the actual weights from data sheets, not estimates. Build your equipment inventory spreadsheet before you touch RISA-3D.

The P&ID tells you what to design for. RISA-3D tells you if your design works. Master the translation between them, and your platforms will stand.