Container Crane; Life Time Extension Possibilities by Iv-Groep

Iv-Consult

WHITE PAPER: CONTAINER CRANE; LIFE TIME EXTENSION POSSIBILITIES

WHITE PAPER: CONTAINER CRANE; LIFE TIME EXTENSION POSSIBILITIES According to the code used for their design, many container cranes are reaching their ‘end of life’. Ordering a new crane is a considerable investment but not always necessary. As an engineering company, Iv-Consult has gained a wealth of experience in life time studies for container cranes. This white paper explains why life time extension could be a suitable option for many existing cranes and how this can be achieved. Iv-Consult has been involved in projects whereby an additional ten years of operation has been achieved with minor costs. A crane is often designed to be in service for

The actual lifetime of the crane’s steel structure is

approximately 2,000,000 cycles. However, there

based on the fatigue damage accumulated during

are many examples of cranes that are used long

usage. Due to the frequent loading of the crane,

beyond their design life. Implementing this safely

micro-cracks form and can propagate and grow

(i.e., guaranteeing a safe piece of equipment for

into critical cracks in the structural steel. Fatigue

the crane operator) is possible with Iv-Consult’s

failure of the steel structure occurs when the

workflow for crane life time extensions.

cracks have propagated to such an extent that the

This white paper provides background

crane can no longer function safely.

information about fatigue, our working methodology and the benefits of a life time

Fatigue failure of the structural steel can be

extension project.

estimated using the so-called Wöhler curve.

1 Fatigue: introduction

(log) Δσ

In consultation with the owner, the crane’s usage is estimated during the design phase. The design usage consists of the expected number of cycles per year, the average and maximum container

Δσa

weights to be handled, the pick-up and set-

down positions of the container, and the desired

lifetime of the crane. Based on these elements, the

engineer designs the crane. However, the actual usage of the crane may differ.

Na Figure 1 - Example of Wöhler curve

(log)

A Wöhler curve (a.k.a. an S-N curve) plots the

For container cranes, not all containers will be

allowable number of cycles to failure (Na) for a

lifted from the maximum outreach above the

specific stress variation level (Δσa), see Figure 1.

vessel and set down at the maximum backreach

The quality of the constructional detail determines

on the quayside. Therefore, it has to be considered

the location of the slope of the S-N curve (1, 2,

that load cycles with various trolley travel ranges

3 etc.) and, therefore, the characteristic stress

will result in a more nuanced fatigue calculation

range corresponding to a number of stress cycles.

than only one travel range. A design spectrum of

For this number of stress cycles, the survival

a crane consists of the various load cycles and the

probability of the steel is 97.7%.

frequency of occurrence during the lifetime.

In various standards, constructional details can be

The Palmgren-Miner rule can be applied to

identified with their Wöhler curve characteristics.

accumulate the fatigue damage of the design

The constructional details are grouped into

spectrum. This rule states that each number of

notch classifications with the same Wöhler curve

stress cycles is proportional to the total number

characteristics. There are notch classes for both

of cycles to failure. Therefore, the damage of

welded and non-welded connections and for

each load sequence can be calculated from

structural members. For welded connections, the

the stress ranges within the sequence, which is

notch class may not only depend on the geometry

then checked against the characteristic fatigue

of the connection but also on the weld quality. An

strength and the corresponding number of cycles.

example of a constructional detail whereby the

Subsequently, the damage per load cycle can

notch class depends on the geometry and weld

be summed, and the total damage to the crane

quality is shown in Figure 2.

calculated. Since the damage is expressed as a unity check, a crane will reach its theoretical end

Δσc Detail Δτc No. N/mm

3.24

of the lifetime when this total damage exceeds 1. Constructional detail

m=3

Continuous component with parts ending perpendicularly 80

l ≤ 50 mm

50 mm < l ≤ 100 mm

100 mm < l ≤ 300 mm

l ≤ 300 mm

Figure 2 - Characteristic fatigue strength Δσc of constructional detail [NENEN 13001-3-1:2012+A2:2018]

2 EN13001 The design codes used 20 years ago were less

An additional benefit is that the EN13001 provides

defined and therefore more conservative. For

more detail categories for the notch effect in the

example, the FEM1.001 defines only four notch

steel structure than older standards, thus resulting

groups, which presents some room for discussion

in a more realistic and nuanced fatigue assessment.

(F.E.M., 1998). However, using only four notch

Extra fatigue life can be achieved as a result. See

groups means that every detail is shifted towards

Figure 3.

the conservative side. The main differences between the old design codes and the EN13001 are discussed in this chapter.

Safety factors

FEM1.001 EN13001

The difference in safety factors for structural Extra life from code

integrity: EN13001 multiplies the load with load factors and safety factors (limit state method) (CEN, 2015), while the FEM 1.001 applies an amplifying

Notch

coefficient to all loads and a dynamic factor to dynamic loads (allowable stress method). We can

Figure 3 – EN13001 has more notch categories than the FEM1.001

conclude that the checks performed on strength

Benefits of life time extension for existing cranes

according to EN13001 usually result in lower unity checks than the calculations according to FEM.

Using a classification for the fatigue lifetime

A different calculation for fatigue life

calculation (e.g., FEM 1.001, DIN 15018) may not

The EN13001 fatigue calculations represent

be in line with the usage of the crane. By applying

the fatigue cycles to failure, which is more

the EN13001, the realized load spectra (possibly

realistic than a classification of the fatigue life.

multiple due to the use of different crane modes in

In the FEM 1.001 calculations, the frequently or

the past) and the number of previous cycles can be

less frequently used parts are given the same

combined with future loads and spectra to analyze

classification (for example, the boom tip versus

the combined fatigue damage. The results from this

the boom at the hinge point). Instead, the

analysis show the remaining lifetime of each part

EN13001 differentiates between these parts. The

of the crane. If there are parts that do not fall within

parts loaded less frequently (such as the boom

the required lifetime, local improvements can be

tip) will benefit from the EN13001 calculation.

designed to extend the lifetime.

Moreover, the indirectly loaded components (such as the portal structure) will benefit from this

Miscellaneous

approach.

The EN13001 code has additional advantages compared to older codes, such as a more nuanced stability check and wheel load calculations. This can be very useful input for the civil calculations of a terminal. However, this topic reaches beyond the scope of this white paper. For more information, please contact Iv-Consult.

3 Modern software Software and hardware are continuously

This tool can check every single weld in a new

improving, creating new possibilities for

design and thereby optimize all weld connections.

engineers. In the past, STS cranes were often analyzed using only beam models since these

For lifetime extensions, problem areas are quickly

can be quickly prepared and modified, often

and accurately identified. By automating the

included code checks, and required low levels of

fatigue calculations, the risk of manual errors

computing power.

is reduced, and lead times are significantly improved. This automation, combined with our

Nowadays, computing power is not an issue and

highly skilled engineers, is beneficial to our clients.

geometries are easily generated or linked to CAD software. Iv-Consult builds detailed parametric

Iv-Consult has developed software to perform

models with the level of detail required for fatigue

fatigue analysis according to, e.g., EN13001,

analysis. This provides an excellent indication

EN1993-1-9 and DNVGL-RP-C203.

of stress concentrations, correct stiffness, the behaviour of joints, and secondary effects such as

4 CO Footprint

in-plane bending stresses.

Extending the life time of your crane has a very General FEA software is, however, not always

positive environmental impact in the long term.

entirely suitable to analyze a crane on fatigue

For example, a modern STS crane has an average

since code checks are not incorporated. Iv-Consult

mass of 1,400 tonnes (MDPI, 2021), taking into

has therefore developed a fatigue analysis tool to

consideration that the carbon footprint of

be used in combination with Ansys Mechanical.

one tonne of construction steel emits roughly

This allows for efficient and automated fatigue

1.9 tonnes of CO2 (NSC, 2010). As a result, the

analysis of the crane welds or other details. The

production of one STS crane has a footprint of

analysis can be based on cyclic or spectral loading

2,660 tonnes of CO2.

(the latter does not apply to onshore cranes). The fatigue damage or the required detail category

The transport of the crane, its coating and the

is visually represented in the 3D model (For an

demolition also carry a significant footprint.

example, see Figure 4).

However, these factors have not been included in the equation for now. A life time extension from 25 to 35 years brings an average of 106.4 tonnes/year back to 76 tonnes/ year, a reduction of approximately 29%. Hence, extending the life of your crane carries a very positive environmental impact in the long term. Several governments, therefore, have subsidies available for such projects to stimulate sustainable

Figure 4 – lowest required notch-group

entrepreneurship. Iv-Consult is happy to assist in applying for these subsidies.

5 Plan of approach Every crane life time extension study is unique.

Crane inspection: When step #iv is complete,

Not only do the crane designs vary, but also the

we have a deeper understanding of which

usage of the cranes can differ (e.g., load spectrum;

parts require closer examination when

stacking function; etc.)

performing an inspection on the crane(s). We prefer to conduct crane inspections together

Our life time extension studies are performed in

with the crane operator and maintenance

the following steps:

personnel. These people are fully aware of any underperforming part(s) of the crane or

Collecting input: Usually, the crane owner

previously experienced issues. This provides

has all the original drawings and calculations

beneficial information in the following steps.

of the crane. Information regarding any

VI. Solutions, calculations & drawings: The

major adjustments to the crane is also

results from steps #iv and #v will be discussed

required for the life time study. Additionally,

with the client. Iv-Consult will advise whether

insight into the usage of the crane, the

local repair or an inspection regime (visual

number of load cycles, and the mass of the

and NDT inspections) will be required for each

lifted containers provides valuable input

item. When repair or modification is needed,

for the analysis. These figures were usually

this will be formulated in detail in repair/

conservatively assumed during the design

modification documents.

process. Using the actual data already

VII. Reporting: All findings will be reported to the

provides an advantage.

II.

III.

IV.

client in a comprehensive report.

In some cases, the crane owner does

VIII. Project management: In coordination with

not possess all information (for instance,

the client, Iv-Consult can also assist with

drawings may be missing). However, with

the RFQ documentation and management.

the experience Iv-Consult has gained, we

Iv-Consult has a wealth of experience in

can conduct reverse engineering to regain

managing crane modification projects. We

missing information. (3D) measurements can

are frequently involved in, for example,

also help recover missing data.

selecting (local) contractors to bid on the

Modelling: Based on the drawings

required modifications, managing the tender

(and, when necessary, on the reverse

process, providing advice with regard to the

engineering), we build our FEA models to

awarding, and managing the construction

simulate the crane structure accurately.

and commissioning process.

Load spectrum: It is vital to have a realistic load spectrum. Changes in conditions may

Electrical and mechanical equipment can be added

also be an essential factor, meaning that the

to the scope of Iv-Consult. Fatigue calculations

damage accumulation should be calculated

can be helpful, and during the inspections, extra

step by step.

attention can be given to specific mechanical and

Analysis: Using the model and the load

electrical parts.

spectrum, we can perform our analysis to investigate when parts of the crane structure

Frequently, the electrical systems should be

will reach their end of life. Any points of

overhauled since they may be outdated by the end

attention will be analyzed in more detail

of the crane’s design life. Mechanical equipment

to gain insight into the accumulation of

may last longer than the crane’s design life (for

damage and the remaining life time.

example, the winch shaft is usually designed for an

infinite life time). Mechanical parts are checked

Upgrading:

during the crane inspection. Wearing parts fall

When considering a crane upgrade (e.g.,

under the OPEX budget and are therefore not

heightening and/or a boom extension), we

included.

strongly recommend first performing a life time analysis to gain insight into whether a crane

6 Financial considerations

upgrade is feasible/realistic. Following this,

A life time analysis provides greater insight into

may be worth consideration.

combining a life extension with a crane upgrade

the remaining life time, the safety of the cranes and the necessary budget reservations.

7 Conclusion

When all the required repairs, modifications and

Using the EN-13001 combined with the fatigue

the required inspection regime is known, an

assessment software as developed by Iv-Consult,

estimate of the involved costs can be generated.

our highly skilled engineers are usually capable of

Usually, the investment and amortization of a

extending the life time of a crane with a minimum

life extension project are far more lucrative than

cost impact. Thereby, a life-time study by

buying new cranes.

Iv-Consult is a lucrative investment.

References CEN. (2015). NEN-EN 13001. CEN. F.E.M. (1998). Rules for the design of hoisting appliances. Manutention, Federation Europeenne de la. https://www.mdpi.com/2076-3417/8/9/1667/htm (appl. Sci-08-01667 p.6). (2018). Retrieved from https://www.mdpi.com manutention, F. E. (1998). Rules for the design of hoisting appliances. F.E.M. MDPI. (2021). Retrieved from Sustainability-08-00807: www.mdpi.com NSC. (2010). The carbon footprint of steel. Newsteelconstruction.com.

About Iv-Consult Iv-Consult is an engineering company specialized in challenging steel and mechanical structures. For decades, we have been working on cranes and crane-related projects daily. Please feel free to download our Cranes brochure.

About the authors Ageet Adriani, MSc (Environment management); Jan de Graaf, MSc (Principal Engineer); Joyce Rietveld, MSc (Mechanical Engineer); Jaco van der Schans, MBA BEng (Sector Manager); Xander Verseveldt, BSc (Project Manager Mechanical) Reviewing team: Andries Kaptijn, MSc (Specialist); Peter Van Kerchove (Technical Director)

Would you like to know more about the possibilities for your project? At Iv-Consult, we would be happy to share our ideas and knowledge and provide a quotation. Email Jaco:

j.m.vanderschans@iv-consult.nl

or call:

+31 88 943 2522