Piping estimates (pt 2)

As part of a continuing series on the role of estimates in project costing, last month we took a look at the costs of pipework and piping projects. Correction factors required in this area fall into two distinct classifications - one covering `area', in which pipework projects can be divided into plant areas that are easy to identify, and the other covering `job' factors. Area correction factors were tabulated on this page last month and included `height' factors and `congestion' factors.

We now turn our attention to the `job' factors. These apply to the total direct manhours and are in turn made up of a labour factor and a distribution factor. Labour correction factors are listed in the adjoining panel, while distribution factors can be broken down as follows:

(1) Unloading from transport within 30m of the site storage or fabrication area for pipe, fittings, etc, and sorting out into storage bins and racks:

Allow 1.5 manhours per tonne

(2) Loading of loose pipe materials onto site transport, delivery and unloading at the erection area (allow extra 0.5 man-hours for every 200m from storage area):

Allow 2.8 manhours per tonne

(3) Loading fabricated pipework onto site transport, delivery and unloading at the erection area (allow for cranage and transport cost as necessary, plus an extra 0.5 manhours for every 200m from storage area):

Allow 3.2 manhours per tonne

There are many tables that give manhour times for the fabrication and erection of pipework, but normally the correlation between maximum achievable times and labour availability is not always defined.

To compile a reasonable estimate, we need to establish the prime factors `skill and effort' of any proposed labour force.

Obviously, judgement will play an important role in deciding labour efficiency. The engineer compiling the estimate should take note of the foreman's appraisal, if available, of his labour force's efficiency.

Failing that, he should consider the reputation of the type of contractor to be used and/or that of the country in which the work is to take place. Where a company has records of the site's achievements on past projects, then clearly these should also contribute to the overall judgement of labour efficiency.

To calculate the actual labour manhours of a pipework project, the following steps should be taken:

(a) Estimate the `area' correction factor (from the `height' and `congestion' tables published last month)

(b) Estimate the `distribution' factor (as explained above)

(c) Estimate the `labour efficiency' factor (from Table 1)

(d) From basic graphs (to be published later) establish the total labour manhour content for the tasks of: handling, unloading, distribution and alignment; jointing (welding, screwing, flanging); installation of pipework, supports, valves, fittings, etc; testing of pipework

(e) Apply the derived factors to the total labour manhours.

{{Labour correction factors

Special labour conditions Factor

Skilled UK labour 1.0Unskilled UK labour 1.2Unskilled foreign labour 1.2Extreme environments (hot/cold) 1.15Excessive supervision 1.05Consideration for adjoining sites 1.05Abnormal working hours 1.20}}

{{Table 1: Labour efficiency correction factors

Assessment of Labour Comparative Work rate Basic tableslabour efficiency labour hour factor enhancementavailability (%) factor (%) factor

Maximum 100 1.00 0.35 0.65Exceptional 95 1.05 0.32 0.68Superior 90 1.11 0.28 0.72Excellent 85 1.18 0.24 0.76Very good 80 1.25 0.19 0.81Good 75 1.33 0.13 0.87Above average 70 1.43 0.07 0.93Average 65 1.54 0.00 1.00

Below average 60 1.67 -0.08 1.08Fair 55 1.82 -0.18 1.18Poor 50 2.00 -0.30 1.30Inferior 45 2.22 -0.44 1.44}}