Electric Heater Skid Piping, Instrumentation and Pressure-Drop Guide

INTRODUCTION

The heater is only one pressure-loss component in a skid-mounted system.

A complete hydraulic review should include piping, valves, strainers, instruments, nozzles, elevation changes and any connected equipment included in the skid scope.

1. Total System Pressure Drop

A simplified system relationship is:

Where each term should be evaluated at the actual operating condition. The static-head term is included only where it is a real net system requirement; in a closed recirculating loop, elevation head may largely cancel over the complete circuit.

For liquids, viscosity can strongly affect pipe and heater pressure drop.

For gases, density changes with pressure and temperature and compressibility may need to be considered.

2. Pump Differential Head

For liquid circulation systems, the pump must provide sufficient differential head to overcome the complete loop resistance at the required flow.

The pump selection should consider:

• heater pressure drop
• pipe friction
• valves
• strainer
• heat exchanger or user equipment if included in the loop
• elevation / static head where applicable
• viscosity
• startup condition
• control valve pressure drop

3. NPSH Review

For pump systems, the available net positive suction head (NPSHa) should exceed the pump required net positive suction head (NPSHr), with any additional margin defined by the pump vendor, customer specification or project standard.

Review:

• suction pressure
• liquid vapor pressure
• tank level
• suction-line loss
• fluid temperature
• elevation
• strainer loss

NPSHa and NPSHr should be checked using the actual fluid, temperature and startup condition. No single universal NPSH margin is suitable for every system.

4. Line Sizing

Line size affects:

• velocity
• friction loss
• pump power
• residence time
• drainability
• material cost
• skid size

Do not select all piping only from nozzle size. The process line should be reviewed from the required flow and allowable pressure drop.

5. Valves

Typical valves may include:

• isolation valves
• check valve
• bypass valve
• drain valve
• vent valve
• control valve where required
• pressure-relief device where included in scope

Valve type and material should match the medium, temperature, pressure and maintenance requirements.

6. Strainers and Filters

A strainer can protect pumps and heater flow passages from debris, but it also adds pressure drop.

Review:

• mesh / filtration requirement
• clean pressure drop
• dirty pressure drop
• cleaning access
• differential-pressure indication
• bypass philosophy if required

7. Drain and Vent

Provide low-point drains and high-point vents where needed for:

• filling
• draining
• air removal
• maintenance
• hydrostatic testing
• freeze protection

Drain and vent routing should consider the actual medium and safe disposal requirements.

8. Thermal Expansion

Hot piping expands.

Review:

• pipe flexibility
• support type
• anchors
• guides
• expansion loops or joints where appropriate
• nozzle loads on heater and pump

The skid frame should not force excessive thermal loads into equipment nozzles.

9. Instrumentation

Typical instruments:

• pressure transmitter (PT)
• pressure indicator (PI)
• differential-pressure transmitter / differential pressure (PDT / DP)
• temperature transmitter (TT)
• temperature indicator (TI)
• flow transmitter (FT)
• flow switch (FS)
• level transmitter / level switch (LT / LS), where relevant

Instrument tags and functions should be shown on the P&ID.

10. Instrument Location

Good location matters.

Examples:

• outlet temperature sensor should measure representative mixed process temperature
• pressure sensors should avoid dead legs where possible
• flow meters require installation conditions suitable for the selected technology
• differential pressure should be taken across the intended component
• local gauges should remain visible and maintainable

11. P&ID

The P&ID should define:

• equipment
• line numbers
• valves
• instruments
• control loops
• vents / drains
• bypasses
• safety devices
• customer interface / battery limits

The P&ID becomes one of the core coordination documents between process, mechanical, electrical and control design.

12. RFQ Data

Provide:

• medium and composition
• flow
• density
• viscosity vs temperature
• operating temperatures
• working/design pressure
• allowable system pressure drop
• pump requirement
• pipe / flange standard
• customer tie-in size
• elevation differences
• instrumentation standard
• hazardous-area classification

Related Xiangyuan Products

Skid-Mounted Electric Heating System

Oilfield Skid-Mounted Crude Oil Heating System

Electric Thermal Oil Heater

Electric Inline Process Liquid Heater

Electric Inline Process Gas Heater

FAQ

Engineering Note

This series is for technical explanation and preliminary engineering reference. Final skid or system design must be confirmed from the actual medium, process duty, pressure, temperature, hydraulic conditions, hazardous-area requirements, electrical supply, control philosophy, site layout, applicable standards, transport limits and agreed supply scope.