Piping installation sequence: what must be done beforehand and where HSOS comes in
A pipeline is built in a fixed sequence – from defining the pipe class through prefabrication, installation, welding and heat treatment to the pressure test and commissioning. Each step requires the previous one to be properly completed. This overview shows the ten phases, what must be done in each phase, where our specialist services come in and what follows. This lets you schedule an HSOS assignment at the right point in the programme.
Four questions before every line
Before the first pipe is cut, four points must be clarified. Almost everything else follows from them – including which of our services will be needed:
The ten phases at a glance
| Phase | What happens | Must be done beforehand | Where HSOS helps | Next |
|---|---|---|---|---|
| 1.Definition and planning | Pipe class, isometric, bill of materials and welding procedure specification are defined. | Plant design, medium and operating data | Technical coordination on bevels, heat treatment and bolting as early as the planning stage | Material ordering |
| 2.Prefabrication | Closure pieces are calculated, pipes cut to length and bevelled, fittings and branches prepared. | Material with inspection certificate on site, dimensions checked on site | Machine cutting and bevelling – dimensionally accurate, repeatable, also on branches | Tack welding |
| 3.Installation | Scaffolding, lifting gear, supports; spools are lifted into place, flanges aligned, connections to pumps and equipment made stress-free. | Steel structure and scaffolding complete, lifting gear suited to the weight | Controlled bolting of flanged joints | Welding |
| 4.Welding | Tack welding and welding to the WPS; depending on the material, preheating and backing gas purging. | Clean bevels, root gap to dimension in the tacked condition, qualified welders | Preheating and maintaining the interpass temperature with records | Heat treatment |
| 5.Heat treatment | Stress relieving of the welds where material and wall thickness require it. | Weld completed, thermocouples attached, supports carrying the line | Heat treatment to the WPS with temperature chart | Inspection |
| 6.Inspection | Non-destructive testing of the welds by the inspection body. | Heat treatment completed | – | Pressure test |
| 7.Pressure test | Insert blinds, fill and vent the line, pressure test, remove the blinds again. | Inspection passed, all supports installed | Opening flanged joints for the blinds and then closing them with a tightening record | Flushing, insulation |
| 8.Completion | Flushing, insulation and heat tracing, strainers upstream of pumps and equipment. | Pressure test passed | Final bolting with tightening record | Commissioning |
| 9.Commissioning | Strainers and last blinds out, plant start-up. | Release by the operator | Re-tightening of flanged joints after heat-up | Operation |
| 10.Operation and turnaround | Leaks, modifications under operating conditions, work during shutdowns. | – | Leak sealing, hot tapping, pipe freezing, flange face machining, composite repair | next shutdown |
Why our work is usually on the critical path
Cutting, bevelling, preheating, heat treatment and bolting all come before the pressure test. If one of these steps is delayed, the pressure test, insulation and commissioning slip with it. That is why we plan our assignments to match the pace of the installation and mobilise at short notice when the schedule changes.
Bolting involves at least two visits: when the joints are closed during installation, and after the pressure test, when the blinds are removed and the joints are finally closed. On hot lines, re-tightening after heat-up is added. Scheduling all three dates early avoids waiting times at the end of the project.
How to prepare for an HSOS assignment
So that we can work productively from day one, these points should be clarified:
- ✓Documents: Isometric or drawing, pipe class, material, wall thickness and – for heat treatment – the welding procedure specification with temperature, holding time and heating and cooling rates.
- ✓Access: Scaffolding, working space around the pipe, power and compressed air connections nearby, lifting gear for heavy machines.
- ✓Permits: Work permit, gas test or hot work permit – or the requirement to work spark-free and cold.
- ✓Condition of the line: Drained, depressurised and isolated – except for work under operating conditions such as hot tapping or leak sealing.
- ✓Contact person: One person on site who can answer questions on dimensions and sequence, and a date for acceptance with a record.
Frequently asked questions
When should I involve HSOS in the planning?
Ideally in the planning phase, at the latest once the pipe class and welding procedure specification are fixed. Bevel geometry, heat treatment and bolting method can then be agreed before material is ordered – for example the stud bolt length if flanges are later to be tightened by bolt tensioning.
Why must all supports be installed before the pressure test?
A filled line weighs many times more than an empty one. Without the final supports, the weight hangs on welds and on pump or equipment connections – this can damage them and distort the test result.
Can HSOS also help after commissioning?
Yes. During operation and shutdowns we seal leaks, hot tap lines under pressure, freeze line sections for isolation, machine damaged flange faces and carry out controlled bolting of flanged joints.
What happens if a flange distorts during welding?
Distortion of the flange face later leads to leaks. Instead of cutting out the flange, rewelding it and heat treating it again, the flange face can in many cases be machined flat on site.
General description based on practical experience, without guarantee. The pipe class, welding procedure specification and operator requirements are authoritative.
Schedule us in good time
Send us the isometric, material and schedule – we will tell you where we fit into the sequence and how long we need.