Practical engineering guide

Specifying a custom weldment or tank

A useful specification describes function, environment and acceptance. A drawing showing only external dimensions is generally insufficient to determine material, welded joints, tolerances and inspection requirements.

Define duty and design conditions

A weldment requires information about loads, supports, interfaces and critical dimensions. A tank also needs medium, volume, pressure and temperature conditions, cleaning, filling and draining details. Material follows the application, not simply the word stainless. A vessel intended for atmospheric service is not automatically suitable for pressure or vacuum.

Treat welding and inspection together

Requirements for joints, procedure qualification, personnel and inspection must suit the product. Welder qualification and welding-procedure qualification address different matters. Assembly dimensional accuracy is separate from allowable weld imperfections. Non-destructive examination methods and coverage depend on material, geometry, function and agreed requirements.

Plan manufacturing and handover

Agree drawing revision, material identification, surface treatment and inspection points before production. Engineering considers joint access, assembly, handling and transport limitations. Where special requirements apply, determine the relevant regime and responsibilities first. Test methods and acceptance limits are defined by competent specialists for the particular product; this checklist does not establish a universal test pressure.

Expected engineering outputs

Approved manufacturing specification and supply boundaries.
Manufacturing approach and appropriate inspection plan.
Dimensional records and agreed handover documentation.

Technical sources and further reading

Reviewed on 18 October 2026. Product limits and applicable requirements are confirmed for each specification.

Selection in context

Pipe and tank materials: an initial comparison

Assess the complete fluid composition including impurities, concentration, temperature and loading; a material family designation alone does not establish product suitability.

On a small screen, scroll the table sideways to compare the selection criteria.

Pipe and tank materials: an initial comparison
Principle or option	Typical application	What to verify when selecting
Carbon steel	Piping and welded vessels where mechanical design and corrosion assessment support its use.	Specific grade, toughness at design temperature, weldability, and corrosion protection or allowance.[1]
Austenitic stainless steel, e.g. 304L	Process piping and tanks requiring cleanability and resistance in an assessed environment.	Chlorides and other impurities, cleaning chemicals, surface finish, crevices and weld-area condition.[3][2]
Austenitic stainless steel, e.g. 316L	An option considered for greater corrosion demands than standard chromium-nickel grades.	The corrosion mechanism, temperature, concentration and cleaning regime; this grade is not universally chloride-resistant.[3][2]
Duplex stainless steel	Equipment where corrosion resistance and mechanical strength are considered together.	Specific duplex grade, service environment, welding procedure and thermal effects; properties vary across the family.[2]
Polypropylene, PP-H	Chemical piping and water treatment where the fluid and service conditions are suitable.	Chemical resistance, allowable pressure versus temperature and service duration, expansion, supports and jointing method.[4]
Polyvinylidene fluoride, PVDF	Selected chemical and clean-process piping with specific system material requirements.	Resistance to the actual mixture, pressure and temperature, process cleanliness requirements, and joint and seal compatibility.[4]

Sources for this comparison

Reviewed on 18 October 2026. Selection is confirmed for the specific operating conditions and equipment design.

Before we start

Questions that shape the project.

Is specifying stainless steel sufficient?

No. Stainless grades differ in resistance and fabrication characteristics. Include medium composition, temperature, cleaning and surface requirements; the material can then be confirmed through technical selection.

Is every tank pressure equipment?

Tanks do not all follow the same regime. Design and operating conditions, together with applicable rules, determine the requirements. The word tank alone establishes neither a conformity category nor the required tests.

Your next project

A clear brief.
A practical next step.

Send your drawings, operating parameters or a short description of the change you need. We will review the technical interfaces and propose the next steps towards a quotation, clarifying any missing information with you.

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