Piping estimates

Last month we started looking at the role of estimates in the costing of a project. We continue the theme this month with a consideration of the costs of piping on a project.

We look first at competitive tenders on lump sum projects. Lump sum is the single total price for work or product covered by agreed specifications or drawings. In most projects in the process industries the cost of pipework can represent a major part of the total project cost. But this cost tends to be underestimated both in terms of resources and monetary value. Pipework systems can work out as high as 70 per cent of the MPI (main plant items) or 50 per cent of the entire plant cost.

No shortcut in the maze

The main problem is that piping consists of a maze of comparatively small, inexpensive parts. Preparing quantity take-offs of pipes, fittings, valves and specials from detailed specifications and piping layouts - and then estimating the cost of material and labour - is an unrewarding task for any engineer. Unfortunately, there is no short-cut through the field of competitive bidding.

Because all sets of specifications and layouts tend to omit necessary details (for example, drainage and vent ports), any estimate must include an intangible contingency item of cost.

Short-cut estimating methods do, however, have a place in the preparation of preliminary estimates and budget estimates. It needs emphasising though that they should not be used for competitive tenders, but rather as a basis for the provision of funding for a project or as an aid to process assessment.

The other type of contract is `cost plus'. This is a general term describing a form of contract where reimbursement is based on the actual cost incurred plus some form of mark-up or fee to cover overheads and profit. An estimate for this type of project forms the basis of a proposal to start the construction project and purchase materials before completion of specification and drawings. In these cases, a lump sum contract is out of the question simply because neither client nor contractor can define the full scope of the project.

As approval of specifications, drawings and so on may need upwards of six months to be forthcoming from the client, and probably the local authority, this time can be used to get documentation ready for competitive bids. Another ten weeks can be lost in obtaining competitive bids and signing the contract, however. A contract on a cost plus basis thus enables a project to save from 36 weeks and more where time is of the essence.

When estimating piping costs certain correction factors have to be applied to any devised standard and used for the distribution, fabrication and erection of pipework. These fall into two simple classifications: `A' Area and `B' Job.

`A' Area correction factors: most pipework projects are divided into plant areas which are easy to identify. Within these areas two factors stand out - height factors and congestion factors, as listed in the accompanying panel.

`B' Job correction factors: these apply to the total direct manhours, being in turn made up of a labour factor and a distribution factor. PE

{{Area correction factors

Height factorsWorking height above grade level Factor

0 > 1.5m 1.03m 1.16m 1.59m 1.7512m 2.2515m 2.7518m 3.25

(For all work above grade level refer to local union agreements)

Congestion factorsClassification Factor

A Plant under construction: pipework in non-congested 1.0exposed positions up to 3m above grade level, locatedin North West using skilled labour

B Plant under construction: non-congested pipework 1.05in pipe tunnels, roof spaces, equipment rooms etc,up to 3m below grade)

C Plant under construction: congested pipe-work in pipe 1.10tunnels, roof spaces etc, below grade level

D Refurbishment/revamp of pipework in 1.15non-congested locations

E Refurbishment/revamp in congested locations 1.20

F Pipework laid on sleepers at grade level 1.02

G Pipework on gantries up to 3m above grade 1.07

H Pipework in trenches up to 3m below grade 1.17}}