Cost-Benefit Analysis: When to Choose ERW Pipe Over Seamless Pipe

Introduction: An Engineering Optimization Problem

The decision when selecting between Electric Resistance Welded (ERW) pipe and seamless pipe is a familiar engineering optimization dilemma of balancing technical performance and economic cost. Although seamless pipe has historically been the default for high-consequence application service, advances in manufacturing and quality assurance techniques for ERW pipe have elevated its technical performance and competitive economic cost for more and more applications.

The purpose of this analysis is to provide a framework based on a rational, quantitative approach, that moves the discussion away from a generalist approach and makes a data-driven decision on what option is suitable for your particular project requirements.

I. A Quantitative Head-to-Head Comparison

A direct comparison reveals the trade-offs in key engineering and procurement metrics.

II. Quantitative Decision Framework: A Project Scenario

To demonstrate this decision-making process, let's review a typical project example:

• Project: a 10-km crude oil transmission pipeline, rural site, Class 1 area.
• Engineering requirement: the line is 16-inch OD pipe with a Maximum Allowable Operating Pressure (MAOP) of 1,480 psi.
• Material: API 5L X52 steel.

Step 1: Verify Technical Sufficiency of ERW Pipe

To begin, we need to assess if an ERW pipe meets the pressure requirement. We had previously used t = P*D / 2*S to determine a minimum wall thickness of 0.316 inches. 

Let's choose a nominal standard wall thickness of 0.375 inches for the seamless and the ERW pipe. A new API 5L X52 ERW pipe can be fully expected to meet the 1,480 psi MAOP and safety factor.

Step 2: Conduct a Cost-Benefit Analysis

Let's now look at the purchase cost of the 10km (approx. 32,800 feet) pipeline.

• Pipe Weigh: A 16" OD x 0.375" wall weighs approximately 62.58 lbs/foot.
• Total Tonnage: 32,800 ft * 62.58 lbs/ft / 2000 lbs/ton ≈ 1,026 Tons.

Let's assume the following approximate costs:

• Seamless Pipe Cost: $1,200 / Ton
• ERW Pipe Cost: $900 / Ton (which is 25% less).

Cost Calculation:

• Seamless Total Cost = 1,026 Tons * $1,200/Ton = $1,231,200
• ERW Total Cost = 1,026 Tons * $900/Ton = $923,400

In this scenario, while the technically acceptable pipe material was identified as ERW, the cost savings realized over the direct material cost for the project represents $307,800 in savings to be redirected to other elements in the project.

III. Decision Summary: Application-Based Choice

Using this quantitative approach, the decision framework is clear:

• Choose SEAMLESS: If your application includes conditions in which no weld is the sole safety factor; examples include extreme pressure and temperature considerations (e.g., critical steam lines, boiler tubes), severe sour service (H₂S) conditions, or specifications requiring extremely thick walls that the ERW process cannot achieve.
• Choose ERW: If a careful engineering analysis shows the pipe's pressure rating and material properties meet the design criteria with an adequate safety factor; examples include a broad category of applications including structural applications (columns, piling), and low to medium pressure transport (e.g. water, oil and gas transmission lines).

Conclusion: The Optimized Engineering Decision

Choosing the "smart" procurement option is not simply to choose the highest specification product, but rather to select the most fit-for-purpose technology for the needs of an application. For a growing number of pipeline and structural applications, modern, high quality ERW pipe is not "compromise"; it is an intentional engineering choice that adds value for performance in conjunction with project economics.